Carbon Monoxide Research Articles

Hydrogen Contaminant Detectors for Ensuring Hydrogen Fuel Quality

The California Energy Commission tracks Hydrogen Refueling Station (HRSs) installations within California and states that there are 66 light duty retail stations open within the State with another 34 in the planning stages.1 The hydrogen dispensed in these stations is expected to meet SAE J2719 standards for the maximum allowable concentration of various impurities.2 Currently HRSs have their fuel analyzed periodically to verify that they meet fuel specifications. However, this implies that any anomaly in the purification system resulting in contaminated hydrogen can result in significant damage to fuel cell vehicles before being detected. Therefore, the development of hydrogen contaminant detectors that can continuously monitor the hydrogen for impurities like Carbon monoxide (CO) and hydrogen Sulfide (H2S) is of great interest. LANL has developed a hydrogen contaminant detector based on a hydrogen pumping cell that is sensitive to < 200 ppb CO and < 4 ppb H2S.3,4 In this talk we will present details of the working mechanism of this hydrogen contaminant detector and present results from the field testing of the detector at a HRS. Acknowledgements This research is supported by the U.S. Department of Energy Fuel Cell Technologies Office, through the Safety, Codes & Standards (SCS) sub-program (Project Manager: Laura Hill).REFERENCES: https://www.energy.ca.gov/data-reports/energy-almanac/zero-emission-vehicle-and-infrastructure-statistics/hydrogen-refueling.San Marchi, E. S. Hecht, I. W. Ekoto, K. M. Groth, C. LaFleur, B. P. Somerday, R. Mukundan, T. Rockward, T; J. Keller, C. W. James, Int. J. Hydrogen Energy, 42(11), 7263-7274 (2017)Brosha, T. Rockward, C. J. Romero, M. S. Wilson, C. Kreller and R. Mukundan, U.S Patent # 10,490,833 (2019).R. Mukundan, E. L. Brosha, C. J. Romero, D. Poppe, T. Rockward, “Development of an electrochemical hydrogen contaminant detector”, Journal of The Electrochemical Society, 167(14), 147507 (2020)

(Invited) Commercialization of CO2 Electrolysis

The atmospheric accumulation of greenhouse gasses such as carbon dioxide (CO2) is the primary cause of global climate irregularities. Over three trillion tons of greenhouse gasses have been emitted since the start of the industrial revolution, and natural disasters such as heatwaves, wildfires, and hurricanes have only increased in regularity. Decarbonization has become an important strategic priority for nations and industries worldwide. Numerous technologies have been developed to capture and store carbon dioxide from the atmosphere. However, most of these approaches do not address the ubiquitous demand for fossil fuel derivatives and their associated petroleum-based infrastructure, nor are these approaches capable of extracting value from the captured CO2.Our company, Twelve, is developing a highly efficient and scalable electrochemical reactor that converts CO2 into valuable building blocks for chemicals and fuels such as carbon monoxide (CO). The resulting CO can be blended with green hydrogen from water electrolyzers to form syngas, enabling an ultra-low carbon pathway to sustainable aviation fuel (SAF) via the Fischer-Tropsch process. Twelve has previously produced SAF for the Air Force, where we demonstrated the first ever SAF pathway based on CO2 electrolysis. Beyond SAF, Twelve has completed commercial projects for chemicals and materials made from CO2 with global brands that include Procter & Gamble and Mercedes Benz. At scale, this technology can enable a closed loop ecosystem wherein CO2, water, and electricity are converted into manufacturing inputs that are currently derived from fossil fuels. We are presently translating the performance of our lab-scale prototypes to the industrial scale, focusing on SAF as our beachhead market.In this talk, Twelve’s CO2 electrolysis technology will be used as a model to describe the commercialization challenges and market opportunities of industrial CO2 electrolysis. Key performance metrics and areas of active collaborative research between Twelve and academic institutions will be discussed. Finally, commercial demonstrations of our technology in the automobile, aviation, consumer chemicals, and apparel industries, as well as our company’s long-term vision and goals will be presented.

Electrodes Modified with Overlayers for Enhanced CO2 Reduction Selectivity

Like many electrocatalytic reactions involving the transfer of multiple protons and electrons, the CO2 reduction reaction frequently exhibits poor selectivity among many possible products. In this presentation, I will describe our laboratory’s efforts to design electrochemical platforms that enable the control over proton transfer dynamics to electrocatalysts using molecular and polymeric overlayers with the goal of increasing product selectivity and understanding reaction mechanism. This platform is generally applicable to both molecular and metallic systems, and we demonstrate how it can be used to improve the selectivity of nonprecious metal O2 reduction and NO3 - reduction catalysts.For the CO2 reduction reaction, this strategy as applied to metal electrodes is also broadly germane and is used to modulate catalyst reactivity such that it results in the selective production of ethylene, ethanol, methanol, carbon monoxide, and methane, with examples for each with Faradaic efficiencies in excess of 70%. A common theme is that the hydrophobicity of the metal-overlayer interface frequently controls product selectivity and can steer the site of protonation events at intermediates. In this manner, for example, the selectivity of catalysts between the C2 products ethanol and ethylene can be dictated. To aid in mechanistic understanding and catalyst characterization, the majority of these studies are conducted on nominally flat metal electrodes. However, we will also describe ongoing efforts to nanostructure these CO2 reduction systems to develop selective catalysts that operate at high current densities.

Changing Mechanisms for CO2 Reduction to Formate Via Protonation of the Catalyst

Electrochemical reduction reaction of CO2 (CO2RR) is a promising method to transform CO2 to useful products for consumption such as formic acid, carbon monoxide, or methane. Simply increasing the driving force of a catalytic process to speed up the rate of CO2 reduction is unviable because of the competing Hydrogen Evolution Reaction (HER) pathway and of increased energy cost. Controlling the reactivity of active intermediates is of substantial importance for such processes. [Fe4N(CO)12]− is a formate selective electrocatalyst previously studied by our group and was modified through protonation and replacement of several CO ligands with triethylphosphines (PEt3) to synthesize [HFe4N(PEt3)4(CO)8] . This PEt3 substituted, pre-protonated analog of [Fe4N(CO)12]− exhibits altered rates compared to a non-protonated analog which we attribute to a switch in mechanism. We further explore explanations for different rates despite similar “active intermediates” and similar driving force using Cyclic Voltammetry (CV).

(Invited) Applications of an AI-Powered, Iot-Based Electrochemical Sensor Platform

Emissions are a significant contributor to climate change [1-2]. Low-cost sensor platforms are needed to understand the levels of emissions and the types of emissions [3]. In addition, sensors are needed to help determine the impact levels of what soon-to-be prominent gases, like hydrogen, will have on the environment [4]. Mixed potential electrochemical sensors are a promising technology for the foundation of the sensor platform [5].Our group has developed an AI-powered, IoT-driven sensor platform capable of measuring and differentiating sources of methane, hydrogen, carbon monoxide, ammonia and oxides of nitrogen [6]. The sensor platform has been field tested at Colorado State University’s Methane Emission Technology Evaluation Center (METEC). Embedded in the system are machine learning methods that are applied to a training dataset collected in the laboratory to quantify the concentration and identify sources of emissions [6]. These results serve as a first demonstration that a low-cost mixed potential electrochemical sensor system can successfully detect underground pipeline emissions and quantify CH4 concentrations that are in agreement with previously published results [7] collected using more complex and costly methods.This talk will focus on the applications of the sensor platform including leak detection, emissions monitoring, tailpipe emissions for transportation, flare management optimization and even methane destruction - all of which support the ability to measure and confirm net-zero strategies.This work was supported by US Department of Energy Award DE-FE0031864.

Stabilization of Metal Alloy Nanocatalysts by Encapsulation with a Metal Oxide

The threat of climate change motivates us to reduce our reliance on fossil fuels and transition to renewable energy infrastructure. Many clean energy technologies including hydrogen fuel cells, direct methanol fuel cells, and water electrolyzers utilize electrocatalysts to generate electricity from chemical energy or vice versa. One direction for increasing the catalytic performance and tolerance to contaminants of the catalyst layers is the development of metal alloy-based catalysts. For instance, ruthenium (Ru) can be alloyed with platinum (Pt) to increase the tolerance of Pt to carbon monoxide, a contaminant that can be found in hydrogen fuel. However, metal alloy catalysts have an additional route for degradation beyond the well-established Ostwald ripening, coalescence, and dissolution mechanisms that are an issue for nanoparticle electrocatalysts. Harsh fuel cell conditions can lead to a separation of the two metals that were originally alloyed in the nanocatalyst and, as a result, this leads to a loss in catalytic performance and tolerance to contaminants.1 This project focuses on the durability of alloyed PtRu electrocatalysts, which facilitate the methanol oxidation reaction in a direct methanol fuel cell and the hydrogen oxidation reaction in a hydrogen fuel cell.This project explored an encapsulation of electrodeposited PtRu nanoparticle catalysts with a porous niobium oxide as a method to stabilize the PtRu alloy. Niobium oxide was chosen due to its high corrosion resistance and previous studies showing its stabilization of Ru.2 PtRu alloyed nanoparticles were synthesized via electrodeposition on a glassy carbon electrode substrate and subsequently encapsulated by an electrophoretic deposition method adapted from Jha et al.3 The morphology and composition of the catalyst and encapsulating layer were characterized by scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and optical microscopy. The activity and durability of pristine and encapsulated PtRu catalysts were evaluated by cyclic voltammetry, linear sweep voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. Carbon monoxide stripping and the double layer capacitance methods were used to study changes in the electrochemically active surface area before and after deposition of the niobium oxide. Access to the electrocatalyst surfaces through the encapsulating layer was maximized by the addition of surfactants and through tuning the potentials applied during the deposition of the niobium oxide as a means to improve its porosity. The niobium oxide was shown to improve the stability of the PtRu alloy and maintain the CO tolerance of the alloy well beyond that of the un-encapsulated catalyst. The stabilization of PtRu imparted by the encapsulation of niobium oxide herein is promising for the stabilization of alloyed nanoparticle catalysts towards a wide range of electrocatalytic applications. Yang, Z.; Yu, X.; Zhang, Q. RSC Adv., 2016, 6, 114014-114018.Jha, G.; Tran, T.; Qiao, S.; Ziegler, J. M.; Ogata, A. F.; Dai, S.; Xu, M.; Thai, M. L.; Chandran, G. T.; Pan, X.; Penner, R. M. Mater. 2018, 30, 6549-6558.

Effects of hydrogen and methane anti-knocking characteristics on the efficiency and power output in argon power cycle engines

Argon Power Cycle (APC) combustion engine has a high efficiency, zero carbon emissions, and zero pollutant emissions, rendering it a promising way for achieving zero or carbon neutrality within the realm of internal combustion engine (ICE) technology. Previous studies have shown that while APCs significantly improve the thermal efficiency of ICEs, they also face serious knock problems due to their high temperatures and pressures, especially when hydrogen is used as a fuel. In this study, the anti-knocking characteristics of hydrogen, methane, carbon monoxide, and ammonia were first investigated in APC through thermodynamic calculations by Ignition Delay Time. Then, based on testbench experiments, hydrogen and methane fuels were selected to further investigate the effect of different fuel anti-knocking characteristics on the indicated thermal efficiency and power of APC combustion engine. Test results showed that when using hydrogen, the APC ICE exhibited a pronounced knock tendency, and the test engine could not operate stably when the excess oxygen ratio <2.1 at compression ratio = 9.6. The CA50 of the maximum efficiency point was delayed in APC than in air for both hydrogen and methane, specially H2 has an obvious lag at about 5–15 ° CA. In comparison, when using methane, the combustion control of engine is easier, and the peak indicated thermal efficiency 59% and the peak indicated mean effective pressure 0.92 MPa are higher than 54.3% and 0.60 MPa of using hydrogen. The use of hydrogen still needs an anti-knocking strategy while an extra carbon capture device is necessary to ensure a closed argon cycle if methane is employed.

Electrocatalytic Conversion of Plasma-Activated CO2 Toward Multicarbon Products

Renewable electricity-powered CO2 reduction reaction (CO2RR) toward chemicals and fuels has been gaining significant attention not only for achieving net-zero carbon emissions but also for enabling long-term energy storage. In electrochemical conversion, CO2 can be upgraded into single- or multicarbon products such as carbon monoxide, formate, and ethylene with remarkable selectivity. However, challenges still exist in terms of high overpotential, limited product range, and low production rates. Moreover, most reported CO2RR to multicarbon products which used Cu as catalysts have predominantly generated C2 products like ethylene or ethanol. However these systems require further performance improvement to target C3+ products which have higher energy density and market price. Another electrified conversion technique involves non-thermal plasma, which can activate CO2 into radical, ionized, and vibrationally excited species at atmospheric pressure and near-ambient temperature. However, plasma processes are non-selective, which poses limitations for controlling reaction pathways and necessitates H2 or light alkanes as co-reactants to produce hydrocarbons.We synergized plasma and electrocatalytic conversion to demonstrate a combined CO2RR process that overcomes the limitations of each individual method. Through the integration of a dielectric barrier discharge plasma and an electrochemical flow reactor, pre-activated CO2 was electrochemically converted on a Cu electrode to produce multicarbon products. The combination enhanced the faradaic efficiency and reaction rate of desirable products and opened new reaction pathways by increasing the activity of CO2 prior to adsorption. The production rates of ethanol, propanol, and acetaldehyde were significantly increased, and new products such as methanol, acetylene, and ethane that were formed only in the combined reaction were detected. The product distribution was studied according to plasma-activated states of CO2 and the electrochemical applied potential. To elucidate the synergistic effects in the combined system, the selectivity and production rates were compared with those in the plasma-only and electrochemical-only reactions. Further control experiments using ground-state reactants were conducted, and the excited states during plasma activation were identified by optical electron spectroscopy. This work represents not only electrocatalysis of pre-activated reactants for enhanced generation of multicarbon products during electrified conversion of CO2, but also demonstrates synergistic convergence of plasma and electrocatalysis for converting reactants possessing strong chemical bonds.

Superior Activity of Carbon Felt Coated with PEDOT and Titanium Oxide Double Layers Towards V(II)/(VIII) Reaction in Redox Flow Batteries

Energy consumption has become a great problem in the last few decades due to the dramatic increment in population and solo dependence on fossil fuels to fulfill energy requirements. The intense consumption of these limited non-renewable resources had harmful effects on humanity, making the adoption of renewable energy resources compulsory. High-efficiency storage systems are necessary for the integration of renewable energy sources into the electrical grid and for the provision of that energy when needed. For this application, all-vanadium redox flow batteries (VRFBs) hold great promise because of their high energy storage capacity, extended operational life, and long-life reusable solutions1. The enhancement of RFBs should be taken from many perspectives such as the enhancement of electrodes, membranes, or even the design of the cell. Enhancing the electrode performance is one of the important challenges that attracted the attention of researchers, with a variety of electrode modifications that have been studied such as using carbon, metals, and metal oxide materials2,3. Over a large number of metal oxides, TiO2 possesses interesting catalytic properties as it has been used in sensors, Li-ion batteries, and electrocatalysis, in addition to its ability to suppress the hydrogen evolution reaction (HER) which was a stumbling block for the negative side of VRFBs4.The goals of this work are to suppress the parasitic reaction of hydrogen evolution and improve the kinetics of the VRFBs' negative half-cell reaction (V(II)/V(III)). To achieve this goal, coating carbon felt (CF) with poly(3,4-ethylenedioxythiophene) (PEDOT) and Titanium Oxide double layers was proposed. The underlayer of PEDOT is expected to enhance the TiOx conductivity, and hence its electrocatalytic activity, but without enhancing the parasitic HER5. The PEDOT layer was formed using chronopotentiometric electropolymerization method, followed by the deposition of a TiOx layer using a solvothermal method. To understand the effect of the PEDOT and TiOx layers on the final electrode activity towards V(II)/V(III) redox reaction, several electrodes (CF\\PEDOT, CF\\G-PEDOT, CF\\TiOx CF\\PEDOT\\TiOx, and CF\\G-PEDOT\\TiOx) were fabricated. The physical and chemical properties of the synthesized electrodes were characterized using XRD, FESEM, EDX, UV-vis DRS, Raman spectroscopy, FTIR, contact angle measurements, and XPS. The performance of the fabricated electrodes towards V(II)/V(III) redox reaction was evaluated in 3-electrode and 2-electrode setups, using cyclic voltammetry, electrochemical impedance spectroscopy, and charging/discharging methods. The addition of an underlayer of PEDOT is found to generally enhance the TiO2 activity as a negative electrode in VRFB. References R. K. Sankaralingam, S. Seshadri, J. Sunarso, A. I. Bhatt, and A. Kapoor, J. Energy Storage, 41, 102857 (2021).Z. Huang, A. Mu, L. Wu, and H. Wang, J. Energy Storage, 45, 103526 (2022).Y. Lv et al., J. Mater. Sci. Technol., 75, 96–109 (2021).J. Vázquez-Galván et al., ChemSusChem, 10, 2089–2098 (2017).M. Heydari Gharahcheshmeh et al., Adv. Mater. Interfaces, 7, 2000855 (2020).

(Digital Presentation) Improvement of Oxygen Reduction Activity on Ti Oxide-Based Electrocatalyst

For widespread utilization of fuel cell system in the future, we have focused on non-precious metal electrocatalyst against high cost of system. Especially, we have studied and reported group 4 and 5 metal oxide-based electrocatalyst as non-platinum catalysts for the oxygen reduction reaction (ORR) because of low-cost, abundant reserves, and high stability in acidic electrolytes [1-2]. We have found excellent ORR activity of Zr oxide-based electrocatalysts prepared from pyrazinecarboxylic acid as a precursor [3-4]. In the case of Ti oxide-based electrocatalysts, the sample prepared under low partial pressure of oxygen with the heat treatment shows high ORR activity when it uses nitrogen-containing porphyrin cyclic organic Ti complexes (TiOTPPz) with multi-walled carbon nanotubes (MWCNTs) as a precursor. However, the heat treatment conditions have not widely investigated yet [5]. In this study, we have investigated to improve ORR activity of Ti oxide-based electrocatalyst prepared from TiOTPPz by varying the oxygen concentration during heat treatment.Oxytitanium tetrapyrazinoporphyrazine (TiOTPPz, [TiOC24H8N16]), a porphyrin cyclic nitrogen-containing organic Ti complex, was used as a starting material. 0.39 g of TiOTPPz and 0.26 g of MWCNT were mixed and treated in a dry ball mill for 1 h to obtain the precursor. The precursor was heated up to 900 oC in an Ar atmosphere and then annealed at 900 oC for 3 h in a low-oxygen atmosphere to obtain a catalyst with precipitated carbon and Ti oxide dispersed on the MWCNTs. The conditions of the hypoxic atmosphere were 2 %H2 + n %O2 / inert gas, with n = 0.05, 0.1, 0.5, 1.0, and 2.0. Catalysts are denoted by TiCNO_(O2 concentration during heat treatment). The catalyst powder was dispersed into 1-propanol with Nafion solution to prepare a catalyst ink. The ink was dropped on a glassy carbon rod, and dried for an hour to use as a working electrode in electrochemical measurement.Electrochemical measurements were performed in 0.5 mol dm-3 H2SO4 at 30 oC with a conventional 3-electrode cell. A reversible hydrogen electrode (RHE) and a glassy carbon plate were used as used as a reference and counter electrode, respectively. Slow scan voltammetry (SSV) was performed at a scan rate of 5 mV s-1 from 0.2 V to 1.2 V vs. RHE under O2 and N2. The ORR current (i ORR) was determined by calculating the difference between the current under O2 and N2.Figure 1 shows oxygen reduction activity of Ti oxide-based electrocatalyst. The vertical axis shows the |i ORR@0.8 V|. The |i ORR@0.8 V| was less than 100 mA gcat -1 at O2 concentrations of 0.05 and 0.1 %, and was greatest at 0.5 % at 413 mA gcat -1. The concentration of O2 further decreased with increasing O2 concentration, and was the smallest at 2.0%. It is suggested that the O2 concentration during heat treatment may have an optimum value around 0.5%.We have also analyzed the catalysts by the XRD before electrochemical measurements. According to XRD spectra, the presence of TiC0.3O0.7 was confirmed in all catalysts. In Ti-CNO_0.5 %, the most active catalyst, the diffraction peaks identified TiO2 rutile and TiO2 anatase were observed. In the case of Ti-CNO_1 and 2 %, the peak intensities of TiO2 anatase increased and the ORR activity decreased. This indicates that the degree of Ti oxidation can be controlled by the atmosphere during heat treatment.Acknowledgement: The authors thank for providing TiOTPPz from Dainichiseika Color & Chemicals Mfg. Co., Ltd.Reference[1] A. Ishihara, Y. Ohgi, K. Matsuzawa, S. Mitsushima, and K. Ota, Electrochim. Acta, 55, 8005 (2010).[2] A. Ishihara, S. Tominaka, S. Mitsushima, H. Imai, H. Imai, O. Sugino, and K. Ota, Curr. Opin. Electrochem., 21 , 234 (2020).[3] Y. Takeuchi, K. Matsuzawa, T. Nagai, K. Ikegami, Y. Kuroda, R. Monden and A. Ishihara, Bull. Chem. Soc. Jpn., 96, 175 (2023).[4] Y. Takeuchi, K. Matsuzawa, Y. Matsuoka, K. Watanabe, T. Nagai, R. Monden and A. Ishihara, Electrochemistry, (2023) in press[5] T. Hayashi, A. Ishihara, T. Nagai, M. Arao, H. Imai, Y. Kohno, K. Matsuzawa, S. Mitsushima and K. Ota, Electrochim. Acta, 209, 1 (2016). Figure 1

Modeling of Fluidized Bed Molten Carbonate Direct Carbon Fuel Cell: Effect of Reverse Boudouard Reaction

Direct carbon fuel cells (DCFCs) are an alternative technology to coal-fired power plants for converting the chemical energy of abundant carbon-rich fuel into electrical energy. DCFCs have higher electrical efficiency and lower greenhouse emissions, which are easier to separate and capture. In the transition to renewable sources of energy, efficient and low-emission technologies need to be explored. Since DCFC technologies are in their early stages of development, modeling and simulation studies are needed to reduce costs and aid in experimental design. In this study, an electrochemical and transport model for a fluidized bed molten carbonate DCFC (FBMCDCFC) is developed. The performance of the fuel cell is evaluated through the polarization losses. This study expounds on recent developments in DCFCs by considering the effect of the reverse Boudouard reaction and the 2-electron oxidation of CO alongside the 4-electron oxidation of carbon at higher temperatures. The electrolyte used is a 62 : 38 mol % Li2CO3/K2CO3 eutectic mixture, while the fuel is activated carbon impregnated by HNO3. The results show that the greatest polarization losses for the FBMCDCFC are from anode activation overpotential and ohmic overpotential. The cathode activation and concentration overpotentials are relatively small. Increasing the reaction temperature results in a greater decrease in anode activation overpotential than ohmic overpotential, despite the increase in CO formation from the reverse Boudouard reaction. The peak power density of the FBMCDCFC is 434.437 W m-2 when operated at 923 K and a gas flow rate of 30 mL min-1. The peak power density of the FBMCDCFC is greater with higher temperatures, where the peak increases to 584.802 W m-2 when operated at 1023 K. The peak power density is greater with lower gas flow rates, where the peak increases to 458.175 W m-2 at a gas flow rate of 25 mL min-1. The mathematical model can aid in optimizing the performance of FBMCDCFCs, such as how increasing the operating temperature favorably increases anode reaction kinetics and reduces ohmic resistances in the cell. Future work will focus on improving the model correlations to close the gap between the results of modeling and actual experiments.Figure 1. a) Power curves at different temperatures, 823 K to 1323 K (30 mL min-1 flow rate, 1 atm total pressure); b) Power curves at different gas (O2 and CO2) flow rates (923 K, 1 atm total pressure) Figure 1

The Electrostatic Stimulation of Adsorbed Carbon Monoxide Oxidation on Pt in Aqueous Acidic Electrolytes

The oxidation of adsorbed carbon monoxide on Pt electrodes, CO(ads)|Pt, in aqueous electrolytes ranks among the most studied reactions in electrocatalysis both from theoretical[1]and experimental viewpoints.[2][3] Much of the interest in this electron transfer process stems from the role CO(ads) plays as an impurity that affects adversely the operation of H2|O2 fuel cells. Consensus appears to have been reached regarding the role of adsorbed hydroxyl, OH.(ads) in controlling the activation and ultimate oxidation of CO(ads). The present contribution illustrates the use of electrochemical stimulation techniques developed in our laboratory[4] to explore new aspects of this process not as yet unveiled by the use of more conventional methods. As described in our earlier publications,[4,5] electrode stimulation refers to changes in the rates of heterogeneous electron transfer processes involving adsorbed species induced by modifications in the electrostatic potential in the solution immediately adjacent to the electrode generated by the passage of current between an electrode placed very close to the working electrode, WE, polarized at constant potential, and a second electrode far away from it. The electrochemical cell used for these experiments consisted of a glass tube covered at each end with custom-made Teflon caps and, thus, similar in design to that described by Qi et al.[4] Experiments were performed in Ar-purged 0.1 M H2SO4 involving CO adsorbed at saturation coverages on polycrystalline Pt, polarized at EWE = 0.8 V, a potential very close to the onset of CO(ads) oxidation with a Au disk electrode placed directly above it working as a stimulating electrode, SE, i.e. face to face configuration. Shown in Fig. 1 are plots of the current flowing through the SE (red), iSE and iWE (black) (see Left Panel) and their expanded views during stimulation (Middle Panel) and CO full oxidation (Right Panel), respectively. As shown in the middle panel in this figure. the passage of a negative iSE, elicits a positive iWE ascribed to CO oxidation, which persists even when iSE turns positive, until the end of the stimulation process (see Right Panel), which takes several seconds. In brief, a single stimulation lasting 140 ms can trigger the full oxidation of the entire adsorbed CO layer in CO|Pt over a subsequent period of ca. 4 s. The most likely explanation for this unique effect may be found in the formation of adsorbed OH. on sites previously covered with CO, as the CV of bare Pt would strongly suggest, which will promote the subsequent oxidation of CO(ads), a process that will propagate through the entire Pt surface. Further support for this mechanism was provided by an experiment in which the WE potential was stepped down to 0.4 V immediately after the stimulation was applied, which stopped virtually instantaneously the further oxidation of CO(ads). Experiments are now in progress to image the surface of the CO|Pt electrode during and after the stimulation to monitor in real time the rates of propagation and to provide a more details theoretical model to account for this phenomenon. References 1 Gao, W.; Mueller, J.E.; Jiang, Q.; Jacob, T. Angew. Chem. Int. Ed. 2012, 51, 9448 –94522 Scott, S.B.; Kibsgaarda, J.; Vesborga, P.C.K.; Chorkendorff, I. Electrochim. Acta 2021, 374, 1378423 Scott, S.B.; Kibsgaarda, J.; Vesborga, P.C.K.; Chorkendorff, I. Electrochim. Acta 2021, 374, 1378444 Han, Q.; Georgescu, N. S.; Gibbons, J.; Scherson, D. Electrochim. Acta 2019, 325, 1349575 Heer, A.S.; Mantelli, H; Han, Q.; Georgescu, N. S.; Scherson, D. in preparation. Acknowledgement Support for this work provided by NSF, CHE-1808592.Fig. 1. Plots of iWE and iSE recorded for EWE = 0.8 V prior, during and following WE stimulation (see text for details) (Left Panel). The middle and right panels show expanded views of the data in the left panel during stimulation and CO full oxidation, respectively. Figure 1

Theoretical Investigation of the Adsorbate and Potential-Induced Stability of Cu Facets during Electrochemical CO2 and CO Reduction

The activity and product selectivity of electrocatalysts for reactions like the carbon dioxide and carbon monoxide reduction reactions (CO2RR and CORR) are intimately dependent on the catalyst’s structure and composition. While engineering catalytic surfaces can improve performance, discovering the key sets of rational design principles remains challenging due to limitations in modeling catalyst stability under operating conditions. Herein, we perform first-principles density functional calculations adopting implicit solvation methods with potential control to study the influence of adsorbates and applied potential on the stability of different facets of model Cu electrocatalysts. Using coverage dependencies extracted from microkinetic models, we describe an approach for calculating potential and adsorbate-dependent contributions to surface energies under reaction conditions, where Wulff constructions are used to understand the morphological evolution of Cu electrocatalysts under CO2RR and CORR conditions. We identify that CO*, a key reaction intermediate, exhibits higher kinetically and thermodynamically accessible coverages on (100) relative to (111) facets, which can translate into an increased relative stabilization of the (100) facet during CO2RR. Our results support the known tendency for increased (111) faceting of Cu nanoparticles under more reducing conditions and that the relative increase in (100) faceting observed under CO2RR conditions is likely attributed to differences in CO* coverage between these facets.This work was partially performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344 and partially supported by the U.S. DOE, Office of Energy Efficiency and Renewable Energy, Advanced Materials & Manufacturing Office.

Electrochemical Conversion of Bicarbonate Using Proton Exchange Membrane-Based Electrolyzer

Direct electrochemical conversion of captured carbon dioxide (CO2) is gaining interest as an efficient method for capturing and utilizing CO2, eliminating the need for energy-intensive CO2 separation process.[1] The integrated electrolyzer with bicarbonate feed operates on the principle of spontaneous reduction of CO2 released from bicarbonate within the electrolyzer. The key to the on-site decomposition of bicarbonate into CO2 is to acidify the bicarbonate within the electrolyzer through the deliberately generated pH gradient. Bipolar membrane has been extensively used to generate pH gradient and acidify the bicarbonate feed.[2] However, the high ionic resistivity of bipolar membrane and slow kinetic of water dissociation reaction can result in a high operation cell voltage.In this study, we demonstrate proton exchange membrane based-bicarbonate electrolyzer which produces carbon monoxide from bicarbonate feedstock with high CO production selectivity and low cell voltage that are comparable to the conventional gas fed CO2 electrolyzer. To achieve highly selective CO production selectivity, a nickel single atom catalyst (Ni SAC) where the atomically dispersed nickel active sites decorated on the nitrogen doped carbon was prepared and utilized. Ni-SAC showed high CO production selectivity even in bicarbonate feed electrolyzer. To further improve the performance of this integrated electrolyzer, significant attention was given to the optimization of electrode structures. Due to the complexity of the reaction environment within the integrated electrolzyer, the performance of the electrolyzer is heavily dependent on the porosity of electrodes and distribution of catalyst on the electrodes. By optimizing the fabrication of electrodes with Ni-SACs, the optimal catalyst coated electrode showed high CO production selectivity over 90% with current density of 100 mA/cm2 at low operating cell potential of 3 V.

Toward Sustainable Olefins: Electroreduction of CO2 to Multi-Carbon Olefins Using Trimetallic Cu-Rich Catalysts

The sustainable conversion of carbon monoxide (CO2) into value-added chemicals via electrochemical methods, powered by renewable electricity, is considered as a promising approach to meet the global energy demand and close the anthropogenic carbon cycle. However, this technology is in the early stage of development, particularly in the production of multi-carbon (C2+) hydrocarbons due to well-studied thermodynamic and kinetic barriers. To overcome these challenges, developing a catalyst with high activity and selectivity is crucial to minimize energy input and maximize the effectiveness of C2+ products formation.In this work, we will present our recent advancement on developing non-precious tri-metallic catalysts with copper-rich surface synthesized by our developed atomically controllable and environmentally friendly synthesis method. The developed nanostructured tri-metallic electrocatalysts by this method show remarkable selectivity and activity in the electrochemical conversion of CO2 to olefins. In particular, our electrochemical results show an overall C2+ olefine Faradaic efficiency (FE%) of 69% more specifically 58% ethylene and 11% propylene at a current density of -112 mA/cm² under applied potential of -2.8 V in an anion exchange membrane (AEM) electrolyzer. To gain a better understanding of the catalytic performance and find a structural-performance relationships for the developed materials, we performed several physicochemical and electrochemical characterization experiments, including X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), and X-ray photoelectron spectroscopy (XPS). We will discuss morphology and atomic structure changes of the developed materials under realistic conditions, with a specific focus on understanding how different trimetallic interfaces influence selectivity and activity in the electrochemical CO2 reduction reaction (eCO2RR).

Effect of Halide Ion Additives during Electrodeposition of Nanocatalysts

Platinum (Pt) and platinum ruthenium (PtRu) alloy catalysts are of interest for the development of green energy technologies such as hydrogen and direct methanol fuel cells. However, the high cost of Pt dictates that the precious metal be used as efficiently as possible so the surface area available to catalyze reactions per mass is maximized. Alloying Pt with different metals such as Ru is also of interest due to the increased activity and tolerance to contaminants that the additional metal imparts to the Pt. Industrial nanoparticle synthesis depends on scalable techniques such as electrodeposition. And a feature of this technique is that the morphology of electrodeposited structures is heavily influenced by the composition of the electrodeposition solution.This work describes how the presence of excess Cl- and Br- ions in an aqueous solution of metal salts affects the morphology of Pt and PtRu electrodeposited onto glassy carbon electrode substrates. The addition Br- ions and mixtures of the two halides resulted in smaller nanoparticles as observed by scanning electron microscopy and, therefore, higher surface areas compared to Pt electrodeposited in the absence of these halide species. Consequently, the mass activity towards the oxygen reduction reaction, one half of the reaction in hydrogen fuel cells, was highest when Pt was electrodeposited in the presence of Br- ions. The PtRu particles were also tested for their activity and resistance to carbon monoxide poisoning as a function of composition and halide additives. These results show that halide ions can be used beneficially in electrocatalyst synthesis without a negative impact on the activity of these catalysts, in contrast to what has been suggested in some prior studies. Presented herein is a simple method to tune the surface area and properties of electrodeposited nanocatalysts.1 Gautam, S.; Hadley, A. M. K.; Gates, B. D. Controlled Growth of Platinum Nanoparticles during Electrodeposition using Halide Ion Containing Additives. J. Electrochem. Soc. 2022, 169, 112508.

Challenges and Opportunities in Preparing Fe-N-C Layers Supported on Non-Carbon Supports

Global energy demand will be continuously rising in the foreseeable future. To mitigate the results of climate change it is necessary to reduce the emittance of greenhouse gases. One promising approach is to switch to hydrogen as energy carrier and use proton exchange membrane fuel cells (PEMFCs) to efficiently convert H2 into electric power. Here, hydrogen and oxygen/air are used to directly generate electrical energy with only water as byproduct. Both reactions need to happen efficiently at the same time. The oxygen reduction reaction (ORR), however, is a very sluggish four-electron-reaction and needs efficient catalysts.The state-of-the-art ORR catalyst in PEMFC is platinum but that is a very scarce and expensive metal. Hence, it is important to switch to precious-metal-group (PGM) free catalysts. In recent years, bio inspired iron-based FeNC catalysts have been shown to approach ORR activities that are competitive with those of platinum, even though they need a higher catalyst loading than Pt to reach the desired high current densities.1–3 Those catalysts feature single Fe atoms surrounded by four N atoms in graphitic carbon. The drawback of those materials is their lower stability compared to PGM materials. In a nutshell, the carbon matrix oxidizes during operation in PEMFCs, changing the morphology of the catalytic center and rendering it less active, or inactive, depending on the carbon oxidation extent. Direct demetallation phenomena are also possible, leaving a N4 cavity without metal cation center. It was shown recently by Wu et al.4 that it is possible to raise durability by adding an additional carbon layer on the catalyst. One alternative approach to reduce those degradations is to interface Fe-N4 sites with a carbon-free support. The targeted support material must be immune to corrosion in acid and withstand the typical ORR electrochemical potentials. It also has to be electrically conductive to facilitate electron transfers, both locally and on long scale.In this work, conductive ceramic metal oxide materials (Ta doped SnO2, TTO) was investigated as a possible alternative catalyst supports. This material is resistant to acid and can withstand prolonged potentials at operating conditions in PEMFCs.5 During the synthesis of the FeNC catalysts, high temperatures are generally applied. Such treatments can be detrimental to the conductivity of ceramics due to metal aggregation (in case of doped materials) and may also lead to morphological changes as well as the reduction of the ceramics to metallic materials. A robust method to synthesize FeNC catalysts is by mixing the separate Fe, N and C precursors and using optimized thermal treatment. In this study, the effect of the pyrolysis conditions as well as the ratio of FeNC precursors to TTO was investigated with various characterization methods, e.g. X-ray absorption spectroscopy, Mossbauer spectroscopy, and high resolution TEM. The characterization techniques confirm the presence of single atom Fe as well as different Sn species that might contribute to the activity. The resulting materials were electrochemically characterized with rotating disc electrode techniques and in PEM fuel cells for their ORR-activity and durability. It was shown that the activity of materials with a high FeNC precursor content relative to TTO can outperform a reference FeNC synthesized similarly but without TTO, in both RDE (Figure) and PEMFC.The presentation will report in detail the effects of pyrolysis conditions and FeNC precursor/TTO content on the structure, activity and stability of materials.(1) Mehmood, A. et al. High Loading of Single Atomic Iron Sites in Fe–NC Oxygen Reduction Catalysts for Proton Exchange Membrane Fuel Cells. Nat. Catal. 2022, 5 (4), 311–323. https://doi.org/10.1038/s41929-022-00772-9.(2) Gasteiger, H. A.; Marković, N. M. Just a Dream—or Future Reality? Science 2009, 324 (5923), 48–49. https://doi.org/10.1126/science.1172083.(3) Zion, N. et al.. Electrocatalysis of Oxygen Reduction Reaction in a Polymer Electrolyte Fuel Cell with a Covalent Framework of Iron Phthalocyanine Aerogel. ACS Appl. Energy Mater. 2022, 5 (7), 7997–8003. https://doi.org/10.1021/acsaem.2c00375.(4) Liu, S.et al. Atomically Dispersed Iron Sites with a Nitrogen–Carbon Coating as Highly Active and Durable Oxygen Reduction Catalysts for Fuel Cells. Nat. Energy 2022, 7 (7), 652–663. https://doi.org/10.1038/s41560-022-01062-1.(5) Jiménez-Morales, et al. Strong Interaction between Platinum Nanoparticles and Tantalum-Doped Tin Oxide Nanofibers and Its Activation and Stabilization Effects for Oxygen Reduction Reaction. ACS Catal. 2020, 10 (18), 10399–10411. https://doi.org/10.1021/acscatal.0c02220. Figure 1

Dynamic Oxygen Collection Efficiency: Unraveling the Effects of Perovskites on Carbon Corrosion As Composite Catalysts for Oxygen Electrode

Introduction The composite catalyst comprising perovskite and carbon has been extensively studied as a catalyst for the oxygen evolution reaction (OER) at the oxygen electrode in alkaline media. However, the competitive corrosion of carbon under harsh OER potential necessitates additional caution when determining OER activity from the overall oxidation current. The use of a rotating ring-disk electrode (RRDE) is acknowledged for its ability to quantitatively determine the faradaic efficiency of the OER. [1] However, for practical applications, the generation of oxygen bubbles can cause unpredictable disturbance, leading to the erroneous collection efficiency. In this study, we aim to establish a dynamic current-response collection efficiency during the generation of oxygen bubbles. This was achieved by modelling with an Au/Au RRDE, well-known for its electrochemical stability under harsh conditions. In addition, using this calibrated collection efficiency, we investigate the influence of perovskite catalysts on the degradation behaviors of carbon materials at OER potentials in alkaline media. Materials and electrochemical measurements Measurements of oxygen gas collection efficiency were conducted using a modeled RRDE comprising an Au disk electrode and an Au ring electrode. The RRDE served as the working electrode, with a Pt wire as the counter electrode, a reversible hydrogen electrode (RHE) as the reference electrode, and a solution of Ar-saturated 1 mol dm-3 KOH as the electrolyte. The disk electrode underwent a 5-minute chronopotentiometry with varied oxidation currents, while the ring electrode underwent chronoamperometry at 0.3 V (vs. RHE). The collection efficiency was calculated from the ring current attributed to the oxygen 2-electron reduction reaction.Two kinds of perovskite catalysts, namely Sr2Co0.8Fe0.2O3Cl[2] (hereafter SCFOC) and LaCoO3 (hereafter LCO), and two carbonaceous materials, namely graphitized carbon black (TOKABLACK#3845, hereafter TB) and ketjen black (EC-600JD, hereafter KB), were used to evaluate the influence of perovskite on the carbon degradation behavior. Four composite catalysts, each comprising perovskite and carbon with a weight ratio of 5:1, were loaded on a disk electrode of the glassy carbon disk/Au ring RRDE. A cell analogous to the aforementioned design was assembled. Electrochemical measurements were conducted through chronoamperometry, employing various potentials at the disk electrode, and maintaining a potential of 0.3 V vs. RHE at the ring electrode, for a duration of 5 minutes. Results and discussion Figure 1 illustrates a three-dimensional representation of the oxygen gas collection efficiency of the Au/Au RRDE as two functions of disk current density and measurement time. It was evident that the oxygen gas collection efficiency varied significantly from the theoretical value (25.6 %) and was dependent on the disk current density and measurement time. The constrained solubility of oxygen in aqueous solution and the hydrophobic nature of the PTFE between the ring and the disk might cause a decrease in the collection efficiency due to the partial retention of oxygen bubbles on the electrode as the oxygen generation current increased and the measurement time elapsed. This suggests that, unlike typical solution reactions, the dynamic determination of the oxygen gas collection efficiency is essential, considering current density and measurement time.Figure 2 illustrates the computation of faradaic oxygen efficiency, utilizing dynamic oxygen collection efficiency. The composite catalyst composed of TB and SCFOC was taken as an illustrative example. The variation in collection efficiency, synchronized with the shape of disk current density, was employed in determining the faradaic oxygen efficiency. This dynamic collection efficiency yielded a comparatively smooth faradaic oxygen efficiency.Utilizing the calibrated faradaic oxygen efficiency, we proceeded to assess the capacity of carbon degradation by integrating the current density of the carbon oxidation reaction (COR) calculated by subtracting the OER current from the overall current. As depicted in Figure 3, the COR capacity as a function of the potential suggested that the components of the composite catalysts had distinct impacts on carbon degradation. Specifically, SCFOC appears to enhance degradation, whereas LCO exhibits a comparatively less pronounced effect.A more comprehensive discussion of these findings will be presented at the upcoming meeting.[1] I.S. Filimonenkov et al., Electrochim. Acta 321, 134657 (2019).[2] Y. Miyahara et al., Chem. Mater. 32, 8195 (2020). Figure 1

Tuning the Bifunctional Properties of Cell Reversal-Tolerant Ir-Pt Electrocatalysts for HOR and Oer

Hydrogen starvation is still a big problem in PEM fuel cells [1]. In order to provide protons and electrons to the cathode during H2 starvation, the carbon oxidation reaction (COR) takes place at the anode [2]. To solve this issue, there are three main strategies: (i) utilization of corrosion resistant support materials, (ii) integration of extensive and complex system mitigation strategies and finally (iii) the addition of co-catalyst to promote the oxygen evolution reaction(OER) instead of COR. [3, 4]In this work, platinum-iridium (PtIr) nanoparticles (NPs) have been designed as a novel bifunctional electrocatalysts to accelerate either the hydrogen oxidation reaction (HOR) or the OER depending on the reaction conditions. Our catalyst concept is the combination of both functionality (HOR and OER) in single Pt-Ir alloy nanoparticles (NPs) deposited on the same support material. The Pt-Ir NPs with Pt:Ir ratios of 1:1 and 3:1 were prepared by two different (colloidal and wet-impregnation) routes. Very interestingly, the oxidation states of platinum and iridium as well as the particle size strongly vary depending on the synthesis route. More precisely, the wet-impregnation enables preparing Pt-Ir NPs of 3 – 4 nm size and mainly in the metallic state, while strongly oxidized NPs with ~2 nm size are produced by colloidal route. Despite the different oxidation states and particle sizes, the Pt-Ir NPs show considerable activity for HOR and OER compared to pure commercial Pt/C and IrOx catalysts. Very interestingly, the bifunctionality of these Pt-Ir is highly reversible and is robust during accelerated stress tests. Operando Quick-X-ray Absorption Near Edge Structure (XANES) spectroscopy were performed to provide fundamental insights into the reversibility and catalytically active states of these bifunctional catalysts under the working conditions by jumping with the potential between HER and OER within few seconds. The combination of operando XANES, RDE and MEA data show that the bifunctional approach is a promising way to improve the cell reversal-tolerant properties of anode catalyst materials compared to the state-of-the-art Pt-IrOx catalyst materials.

Removable Photocatalysis Microneedle Reactor for Carbon Monoxide Delivery to Enhance Chemosensitization.

Carbon monoxide (CO) has emerged as a promising therapeutic agent, yet ensuring safe and precise CO delivery remains challenging. Here, we report a removable hydrogel-forming microneedle (MN) reactor for CO delivery via photocatalysis, with an emphasis on chemosensitization. Upon application, body fluids absorbed by the MNs dissolve the effervescent agents, leading to the generation of carbon dioxide (CO2) and triggering the release of the chemotherapeutics cisplatin. Meanwhile, the photocatalysts (PCs) trapped within MNs convert CO2 to CO under 660 nm light irradiation. These PCs can be removed by hydrogel-forming MNs, thereby mitigating potential biological risks associated with residual PCs. Both in vitro and in vivo experiments showed that MN-mediated CO delivery significantly improved tumor sensitivity to cisplatin by suppressing DNA repair, using an A375/CDDP melanoma model. This removable photocatalysis MN reactor offers safe and precise local delivery of CO, potentially creating new opportunities for CO or its combination therapies.