Anodic Current Research Articles

Non-Isothermal Operation of Membrane Electrode Assembly-Based CO2 Electrolyzer for Enhanced Energy Efficiency

The utilization of membrane electrode assemblies (MEA) in carbon dioxide (CO2) electrochemical conversion showcases the promising potential for stable and scalable industrial applications in fuel production, attributed to efficient gas diffusion and minimized system resistance. The electrochemical performance of MEA-based CO2 electrolyzers relies on the chemical reactivity and product selectivity optimization which is dependent on three factors: CO2 mass transport, charge transport, and ionic transport. Elevating the overall system temperature benefits the performance of the oxygen evolution reaction (OER) at the anode. Furthermore, the elevated temperature enables higher conductivity of anion exchange membranes (AEM), thereby further diminishing cell voltage. However, the downside emerges as CO2 solubility decreases at higher temperatures, fostering a scenario where the catalytic reaction leans toward hydrogen evolution, thereby undermining product selectivity.Herein, we propose an innovative approach involving thermal management for separate temperature control for the anode and cathode, forming a non-isothermal MEA by maintaining an elevated anodic temperature while cooling the cathode. This approach simultaneously addresses the need for a high-temperature anode and a low-temperature cathode. This study exhibits a temperature gradient of approximately 20°C between the anodic and cathodic planes achieved through efficient thermal modulation of water cooling and heating within the electrode plates.We showcase the benefit of non-isothermal operation with an Ag-based cathode and IrO2-based anode using 1 M KOH as the anolyte for CO2 conversion into CO. The non-isothermal condition, i.e., maintaining an anodic temperature of 80°C and a cathode temperature of 60oC, demonstrated a 65% enhancement in CO partial current density (j co), 195.6 mA cm-2, compared to the isothermal 80°C condition, 118.6 mA cm-2. The optimal performance across all temperature regimes is found to be the non-isothermal condition with anode temperature at 60°C and cathode temperature at 40 oC, yielding a j co of 243.5 mA cm-2 at 3.25 V, marking a 13.3% improvement over the isothermal 60°C condition (j co = 214.9 mA cm-2). The increase in the j co can be attributed to the lower temperature at the cathode (40 oC for the non-isothermal condition vs. 60oC for the isothermal ccondition) resulting in higher CO faradaic efficiency.The CO faradaic efficiency remained above 80% (cell potential < 2.7V) for the non-isothermal 60°C condition, whereas it dropped below 80% throughout the entire region cell potential range for the isothermal 60°C condition. This study presents a novel non-isothermal operation for advanced thermal management for MEA-based CO2 electrolyzers for simultaneous enhancement in anode activity as well as cathode selectivity. We believe this thermal management strategy is promising for engineering high-performing MEA-based CO2 electrolyzers at industrial scales.

Potential-Dependent BDAC Adsorption on Zinc Enabling ‘Selective’ Suppression of Zinc Corrosion for Energy Storage Applications

Utility-scale zinc (Zn) batteries are a promising solution to address the problem of intermittency of renewable energy sources[1],[2]; however, Zn-metal anodes in these batteries suffer from capacity loss due to spontaneous corrosion of the Zn especially when high-surface area anode configurations are employed[3]. Additionally, Zn dendrites are known to form during battery charging which limits the cycle-life of these batteries. Electrolyte additives have been explored that prevent the aforementioned issues[4],[5], but these too come at a cost, i.e., surface-blocking additives polarize the electrode surface leading to loss in the voltaic and energy efficiencies of the battery. In this presentation, a novel electrolyte additive, benzyldimethylhexadecylammonium chloride (BDAC), will be presented for its ability to suppresses corrosion of Zn in a mildly acidic (pH = 3) electrolyte. An attribute of BDAC distinct from previously studied additives is that it ‘selectively’ suppresses corrosion when the Zn electrode is held near its mixed potential; however, during high-rate Zn deposition (charging) or stripping (discharging), BDAC is essentially deactivated and thus does not appreciably polarize the electrode surface. This selective corrosion suppression behavior is explored using slow-scan cyclic voltammetry, which reveals a hysteretic response. The response implies a current-dependent BDAC adsorption mechanism in which BDAC reaches higher surface coverages when the partial currents at the Zn surface are low (e.g., at or near the corrosion mixed potential), but BDAC coverage is reduced considerably when the Zn deposition-stripping rates are increased. Numerical simulations of the BDAC diffusion-adsorption process are used to corroborate this model. Ramifications of our approach to the selective suppression of Zn dendrites will also be discussed.

Upcycling Compact Disks to Flexible Nanoporous Gold Electrodes for Nitrite Biosensing

Electrochemical biosensors are crucial in disease detection due to their simplicity, rapidity, and sensitivity. As a wearable or e-skin platform, electrochemical sensors are frequently restricted by gradual degradation, complexity, limited active surface area, arduous fabrication process, and high cost. Therefore, soft electrochemical biosensors that are mechanically biocompatible, easy to prototype, and robust for sensitive biosensing are highly sought. To mitigate such an issue, recordable compact disks (CDs) have been upcycled to advanced biosensors exhibiting flexible and disposable and being applicable to various biomedical applications, making them an economical and practical option. However, the limited surface area of the gold CDs electrode prevents optimal electrochemical catalytic performance. Nanostructure has been widely embedded in electrochemical biosensor construction to optimize electrode surface area and the number of active sites, which can contribute to improved detection sensitivity, selectivity, and electron transfer.Here, we aim to develop an advanced nanoporous gold film electrode (NPGFE) from CD for a simple, flexible, sensitive, and larger surface area electrode with reproducible areas. The fabrication and modification of gold CDs film were accomplished through two steps: 1) A mechanical cutter tailored the gold film after being transferred from CDs into a flexible substrate (Polyimide tape). Before placing the CDs film between the two laminating sheets, an aperture (1 mm diameter) was made in one of the laminating sheets to expose the tailored gold film electrode (GFE) and insulate the undesired area using a thermal laminator to ensure an adequate seal as a simple and low-cost approach; 2) The nanoporous gold (NPG) was electrochemically deposited onto the gold CDs film surface in gold (III) chloride trihydrate (HAuCl4·3H2O) and ammonium chloride (NH4Cl) solution at a potential of -4V for 100 s. Surface morphology characteristics and elemental analyses were investigated using scanning electron microscopy, while electrochemical studies were carried out in the CH Instruments potentiostat.The SEM images confirm a homogeneous distribution of NPG across the electrode’s surface. The energy-dispersive X-ray analyses exhibited the purity of the deposited NPG. The effective surface area was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in 1 M KCl and 1 mM K3[Fe(CN)6] solution. From the slope of the Ip vs. v1/2 plot and the Randles-Sevcik equation, the active surface area of the NPGFE was significantly increased compared to the unmodified GFE. EIS was conducted to evaluate electron transfer resistance and obtain the semicircular diameter in Nyquist plots. In comparison to the unmodified GFE, the NPGFE showed a semicircle with a smaller diameter, indicating that the electron transfer resistance is minimized. The electrochemical characterization of the NPGFE was investigated by CV and amperometric techniques in 0.1 M PBS solution at ambient temperature (25°C) and pH 7.4. The NPGFE performance was studied at a fixed potential (0.77 V vs. Ag/AgCl) by analyzing the current response upon adding nitrite and anodic peak current at a potential range from 0.3 to 0.9 V (vs. Ag/AgCl). The calibration curve plot was linear over 0.5 μM to 9 mM with 20 nA·μM−1·cm−2 sensitivity and a low detection limit of 0.5 μM with a correlation coefficient (R2) of 0.99. The NPGFE's reproducibility reusability studies were conducted to evaluate electrode stability when prepared independently and utilized repeatedly under the same condition. Results demonstrate remarkable reproducibility and highly satisfactory reusability, making it suitable for practical application. The effect of pH on nitrite detection was investigated at different pH values. The anodic peak currents decreased and shifted to the low potential when the pH was increased from 5.0 to 10.0, indicating that protons were directly involved in the nitrite redox reaction. Also, the selectivity studies showed a significant increase in the current response when nitrite, ascorbic acid, and sodium sulfite were introduced to the solution, and there were no remarkable changes when other interferents were added. The long-term stability results showed that the NPGFE retains 99% of its initial current response to NO2 - after six months of storage, indicating satisfactory stability and long service life of NPGFE. Importantly, the sensing performance while stretching the NPGFE will be investigated to produce biocompatible relevant results.The flexible, nanoporous upcycled CDs electrode utilizing craft machines provide fast prototyping electrochemical biosensors for skin-interfaced bioelectronics. The nanoporous CD-based biosensor significantly improves electrocatalytic performance toward nitrite detection along with exceptional improvements in the cost-effective and sustainable fabrication process for flexible electronics. Future work relies on developing system-integrated biosensors based on systematic reliability and feasibility tests. Soft upcycled bioelectronics holds significant potential in advancing biomedical in situ real-time analysis in various platforms of flexible and nanostructured biosensors. Figure 1

Effect of Electrolyte Composition over CO2 Reduction

The rapid utilization of fossil fuels escorted by an excess of CO2 emissions has led to global energy and environmental crisis. Therefore, the necessity for a clean, renewable and sustainable source of energy is a growing concern for the present and future society. In this regard, economically viable CO2 reduction would be a critical turnover in research, as it has the potential to fulfil a substantial need for clean energy. However, even though many efforts have been done in this field, there is still room for improvements concerning efficiency, material stability, and catalytic enhancement in regard of kinetics and selectivity. Herein, we provide the experimental proof for enhancement of the CO2 reduction efficiency and selectivity from the SEI (semiconductor-electrolyte interface) side through the use of carbonates, borates, sulphates and alkali cations as the electrolyte as well as an overview of the latest developments on Cu2O based PEC CO2 reduction for solar fuel production. Cu2O is a low-cost semiconductor and one of the most promising candidates for PEC CO2RR. However, its stability and performance is still unsatisfactory, thus the CO2 reduction products vary from one investigated system to another, such as: CH3OH, CO, HCOOH, CH3COOH, and CH3CH2OH. Moreover, the instability of Cu2O causes it, to be rarely used for the routine CO2 reduction reaction. In this paper, we use a very facile electrodeposition method, which offers a high level of reproducibility and the possibility of using a new electrode in each experiment, in order to focus our efforts on following the phenomena occurring in the double layer during the photocatalytic run. In this way, we were able to correlate the final CO2RR performance with a reorganization of the cations and anions near the photocatalyst surface. It is shown in the literature that factors such as: carbonate concentration, local pH, the presence of alkali metal cations, the geometry of the anionic group, CO2 solubility, conductivity, as well as pH changes along with the number of H+ in the electrolyte, play a significant role in regulating the partial CO2RR current. In this paper, we would like to shed new light on the influence of the electrolyte composition, cation-anion interaction and local reaction environment around the catalyst on the performance of CO2RR. We found out that the specific interaction between the alkali cation and the anionic group of particular geometry contributes to the formation of a kind of a “rigid layer” within the double diffusion, close to the photocatalyst surface layer, which accounts more for an apparent CO2RR current than the decrease in the finite Warburg element, which is a central key parameter for the diffusion coefficient values. The effectiveness of the strength of the cation-anion interaction in the formation of the “rigid layer” around the photocatalyst surface is found to increase the PEC CO2RR performance. Elucidating this mechanism provides useful information for creating further experimental design and the new pathways for addressing highly efficient PEC CO2RR systems. The authors have noticed a significant knowledge gap in the existing literature, as no prior publications have delved into the concurrent and combined impact of both cations and anions on PEC CO2RR. In this pioneering publication, we present the inaugural investigation of this this intricate phenomenon.

Designing Better Li Metal Anodes for Next-Generation Batteries

Li metal batteries have the potential to significantly advance battery technology due to their substantially higher energy densities. However, robust high-capacity Li metal anodes are necessary to realize this approach, and current Li metal anode designs suffer from significant degradation over time due to non-uniform Li plating/stripping during cycling, which can lead to dead Li and/or Li dendrite growth. Carbon scaffold hosts can help mitigate this problem by creating a uniform electric field and providing abundant Li nucleation sites, but the relationship between the host architecture and performance is not well understood. We investigated the effect of scaffold architecture and chemistry on the resulting Li morphology and electrochemical performance using a combined experiment/theory approach. Carbon scaffolds with well-controlled geometries and varied porosities were fabricated using 3D printing and then characterized by SEM, Raman, and XPS before cycling in cells to evaluate their performance as hosts for uniform Li plating/stripping with both liquid and solid electrolytes. Atomistic and mesoscale modeling were used to predict how scaffold chemistry and microstructure affect Li nucleation probability and the formation of current density/stress hotspots that can lead to dendrite growth, and these results were used to help guide scaffold design. This work provides further insight into the relationship between anode architecture and Li metal cycling stability, which will facilitate the development of high-energy-density batteries in the future.Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344.

A Thermal Tanks-in-Series Model for Simulating over-Discharge Cycling in Lithium-Ion Batteries

Energy storage will play a crucial role in the transition to clean and renewable sources of energy production to meet future consumption demands.1 Lithium-ion (Li-ion) batteries are widely adopted due to their high energy density, low self-discharge rate and fast charging capabilities for applications like electric vehicles and grid storage.2 Li-ion batteries for high voltage operations, where several cells are connected in series, can experience inadvertent over-discharge due to differences between cells3,4. These differences can arise due to many reasons including changes in internal resistance and deviation in electrochemical degradation that can cause divergence of cell open circuit potentials. Over-discharge is a condition when the manufacturer recommended lower voltage limit is crossed while discharging4, which results in various side effects such as electrolyte decomposition, capacity degradation, cathode morphology change and possible internal short circuit3,5. Increase in anode potential during over-discharge leads to copper dissolution from the anode current collector and subsequent plating within cell components. The Solid Electrolyte Interface (SEI) can decompose during excessive deintercalation and reform during charging, reducing the lithium inventory. Excessive heat generation during cycle life testing after occurrences of over-discharges has been found in some cases to lead to temperatures >150 °C6,7.Temperature plays a key role in the electrochemical performance of individual cells, affecting the diffusivities of ions, kinetics of reactions and rate of degradation of the battery. A physics-based modeling approach coupled with a thermal model can be employed to understand the effect of over-discharge on the electrochemical behavior of Li-ion batteries and provides insights into the interplay of various degradation mechanisms that cause capacity fade.The Thermal Tank-In-Series9,10(TTiS) model is a systematically volume-averaged form of the standard pseudo-2-dimensional (p2D)11 model with energy balance equations for the current collectors, cathode, separator and anode. This reduces the number of equations in the model and improves computational speed while maintaining accuracy, as it is sensitive to changes in the battery’s state of charge (SOC) and cell temperature, which helps predict the overpotential changes to the cell electrodes and thermodynamics.We use the TTiS model to identify the dominant fade mechanisms in 3 sets of experimental cycling and temperature data for the: i) normal operating window (2.5V – 4.2V), ii) 5 initial cycles of over-discharge (1.5V – 4.2V) followed by normal operation until 20% capacity fade and iii) 5 cycles of periodic over-discharge every 20 cycles, until 20% capacity fade. Analysis on the effect of C-rate, ambient temperature and voltage window of operation will facilitate understanding the temperature behavior and overpotentials in a cell sandwich. Key considerations required in extending a model to simulate over-discharge will also be examined. References S.P. S. Badwal, S. S. Giddey, C. Munnings, A. I. Bhatt, and A. F. Hollenkamp, Frontiers in Chemistry, 2, 28 (2014).G. Pistoia. Lithium-Ion Batteries: Advances and Applications. First ed. Elsevier, Amsterdam (2014).R. Guo, L. Lu., M. Ouyang, X. Feng. Sci Rep 6, 30248 (2016).G.Zhang, X. Wei, S. Chen, J. Zhu, G. Han, and H. Dai. J. Power Sources, 521, 230990. (2022).C. Fear, D. Juarez-Robles, J. A. Jeevarajan, and P. P. Mukherjee, J. Electrochem. Soc., 165, A1639–A1647 (2018).D. Juarez-Robles, Purdue Univ. Ph.D. Thesis (2019).H. Maleki and J. N. Howard, J. Power Sources, 160, 1395–1402 (2006).H. Liu, Z. Wei, W. He, and J. Zhao, Energy Convers. Manag., 150, 304–330 (2017).A. Subramaniam, S. Kolluri, S. Santhanagopalan, and V. R. Subramanian, J. Electrochem. Soc., 167, 113506 (2020).A. Subramaniam, S. Kolluri, C. D. Parke, M. Pathak, S. Santhanagopalan, and V. R. Subramanian, J. Electrochem. Soc., 167, 013534 (2020).M. Doyle, T. F. Fuller, and J. Newman, J. Electrochem. Soc., 140, 1526 (1993)

Carbon-Coated Mesoporous Silica Nano-Quills from Bioderived Cellulosic Templates for Low-Cost Anodes

The escalating global energy demands, driven by population growth and the electrification of transportation, have positioned rechargeable lithium-ion batteries (LIBs) as critical components in phasing out traditional fuel-based technologies. To date, several high-capacity active materials have been developed to replace current graphite-based anodes for boosting the energy density of LIBs. Silicon dioxide (SiO2, or silica) has emerged as a promising alternative, with a high theoretical capacity of 1965 mAh g-1, five times higher than conventional graphite, along with a comparatively smaller volume change than elemental Si during battery cycling. In this study, we report a patented synthesis process that harnesses wood-derived cellulose nanocrystals (CNCs) to craft a unique three-dimensional (3D) silica architecture for developing low-cost LIB anodes. Our cost-effective method yields a mesoporous silica material, termed silica nano-quill (SilicaNQ), with distinctive hollow 1D arms. In addition, we propose a direct annealing strategy for transforming CNC templates into a conformal carbon coating to fabricate SilicaNQ@C powder material. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) provided a detailed exploration of the elemental composition and the bonding states at the atomic level. Anodes comprising SilicaNQ@C active material delivered a stable reversible capacity of 1030 mAh g-1 after cycling at 200 mA g-1 for 200 cycles. We performed X-ray diffraction (XRD) measurements on SilicaNQ@C half cells to identify phase changes at various state-of-charge levels and explore the evolution of interface components over cycling.

(Battery Student Slam 8 Award Winner) Evaluating Electrodeposited Tin and Antimony-Based Anodes for Sodium-Ion Batteries

The widescale adaption of intermittent renewable energy sources, such as wind and solar, must be accompanied by a grid storage network to store energy when it is abundant and redistribute it as needed for on-demand use. Short-term storage in the form of rechargeable batteries is an attractive avenue for meeting these storage needs. The dominant technology in today’s market, the lithium-ion battery (LIB), is cost-prohibitive due to the need for rare-earth materials. Using the same working principle as LIBs, sodium-ion batteries (NIBs) utilize earth-abundant, low-cost sodium compounds instead of lithium compounds. Tin (Sn) and antimony (Sb) alone are promising anode materials for sodium-ion batteries with high theoretical capacities (847 and 660 mAh/g for Sn and Sb with Na, respectively) relative to current LIB anode chemistry (372 mAh/g) [1,2]. When combined, SnSb has shown to have increased stability relative to Sn or Sb alone [3]. Here, we synthesized Sn-Sb thin films with varied Sn and Sb atomic ratios by co-electrodeposition from a deep eutectic solvent by modifying solution stoichiometry and electrodeposition parameters. Using a combination of X-ray photoelectron spectroscopy (XPS), X-ray diffraction, and energy dispersive X-ray spectroscopy (EDS), phases and compositions of Sn-Sb synthesized by electrodeposition were identified. Once synthesized, we sought to determine the influence of morphology, surface chemistry, and composition on the capacity retention and rate capabilities of Sn and Sb-based anodes in NIBs. An optimized electrode composition was identified using a carbonate-based electrolyte, which resulted in stable capacity retention cycling at a rate of C/2 for 270 cycles.[1] W. T. Jing, C. C. Yang, and Q. Jiang, Journal of Materials Chemistry A, 8, 2913–2933 (2020).[2] S. Megahed and B. Scrosati, Journal of Power Sources, 51, 79–104 (1994).[3] W. P. Kalisvaart, H. Xie, B. C. Olsen, E. J. Luber, and J. M. Buriak, ACS Applied Energy Materials, 2, 5133–5139 (2019).

Microtubular Electrodes for Efficient Electrochemical CO2/CO Reduction to Value-Added Products

The conversion of carbon dioxide (CO2) or carbon monoxide (CO) to commodity fuels and chemicals, empowered by low-carbon electricity, has attracted much attention as an alternative to conventional routes of chemical production [1]. Numerous studies have focused on CO2 reduction to CO or formic acid and active/efficient electrocatalysts with high Faradaic efficiencies (FEs) have been developed [2]. However, CO2 reduction to higher value C2+ products needs the critical C-C coupling step, and to date, Cu has been the main electrocatalyst for this conversion [3]. Electrochemical carbon monoxide reduction (CORR) to C2+ products has advantages over electrochemical CO2 conversion (CO2RR) as issues such as carbonation, and CO2 loss during CO2RR are omitted in CORR due to the stability of CO in alkaline solutions. Facing common challenges as CO2RR, CORR suffers more from mass transport resistance and intrinsically lower aqueous CO solubility. Therefore gas-diffusion electrodes (GDEs) are desired to boost the formation of triple phases and active sites to obtain higher reaction rates.Herein for the first time we design Cu-based HFGDEs for efficient CORR to C2+ products with ethylene as the main product. The pristine Cu HFGDEs showed low selectivity towards C2+ products. Therefore, we tuned the Cu catalyst shape morphology and orientated growth of nanocubes on the outer surface of HFGDEs by electrodeposition. Due to the efficient C-C coupling and high C2+ _selectivity of copper nanocubes with dominant Cu(100), the HFGDEs showed exceptionally high current densities in the 1.0 M KOH electrolyte, outperforming conventional GDEs tested for CORR under similar conditions. Compared with CO2RR in a bicarbonate medium, significantly higher current densities and FEs of C2+ products (>90%) and ethylene (>65%) were achieved when the HFGDE were used for CORR. Moreover, lower partial current densities of C2+ were obtained when using the hollow fibers in the non-GDE mode, confirming the significant performance of HFGDEs for achieving high-rate and selective CO reduction through maximizing triple-phase interfaces and local CO concentration. By increasing the concentration of KOH, an ethylene partial current density of 472 mA cm2- was obtained using the flow-cell reactor, indicating the promises of HFGDEs as an emerging electrode configuration for efficient CORR to C2+ products. Figure 1

(Invited) Green Ammonia Production from Electrochemically Upcycling Waste Nitrogen in an Membrane-Free Alkaline Electrolyzer

NH3 is an essential nutrient for life, but its production through anthropogenic N2-fixing process has caused alarming damages to ecosystems and human health. Excessive NO3 - leakage into water bodies due to overfertilization has led to the formation of "dead zones" in coastal areas. Denitrification generates N2O, which is 300 times more potent than CO2. Restoring the balance between the generation and elimination of Nr is an urgent task for humanity. Efforts to address the negative impact of human-generated Nr have focused on converting it to harmless N2 or improving its utilization in the nitrogen cycle. One promising method is electrochemical conversion, which can eliminate Nr without additional oxidants/reductants. However, achieving selective NO3RR toward N2 is challenging. An alternative approach is to convert other forms of Nr to NH3 in an electrochemical reactor, which could reduce the environmental impact of Nr and decrease the NH3 demand from the Haber-Bosch process, while also reducing the use of fossil-derived H2.In this work, we report our work on the development of a membrane-free alkaline electrolyzer (MFAEL), which transforms Nr into NH3 as the sole N-containing product. With the inexpensive and robust MFAEL system, we achieved an ampere-level partial current density towards NH3 production. By properly choosing the conditions of NH3 collection from MFAEL, continuous production of pure NH3-based chemicals can be realized without the need for additional separation procedures. Techno-economic analysis (TEA) suggests the potential economic feasibility of the waste-to-NH3 process by coupling electrodialysis (ED) for Nr concentration and the MFAEL process for Nr conversion, offering an all-sustainable route for upcycling waste N into the highest-demanded N-based chemical product. Our recent efforts on green-ammonia capture CO2 and reduction to valuable chemicals will also be briefly presented.

Cu-Containing Metal-Organic Framework Electrocatalyst for Efficient Production of C2+ Compounds via CO2 Reduction Reaction

The electrochemical reduction of CO2 (CO2RR) is a promising strategy to yield valuable carbon-containing products and mitigate current environmental and energy issues. Cu-based MOF electrocatalysts have great potential for the selectivity of C2+ products due to their unique property. However, the rational design of active sites in Cu-based MOFs needs to be further studied. In this work, we propose a strategy to evolve abundant partially oxidized Cu species by applying a negative potential prior to CO2RR on Cu-MOFs, which results in high faradaic efficiency of 78% and partial current density of −46 mA cm−2 at −0.95 VRHE towards multi-carbon products. The electrochemical activation of Cu-MOFs can lead to the shift of superficial chemical state from Cu2+ to Cu+. Interestingly, the conversion rate is varied by different thermal annealing times on the pre-catalysts. Thereby, the relative concentration of Cu+ species can be quantitatively compared before and after activation to reveal the dependence on those FEC2+. The insights gained from this study can provide valuable guidance for the design and development of efficient Cu-MOF catalysts for the production of C2+ products.

(Invited) Graphene Oxide As an Additive for Ni-Fe Electrodeposition

In contrast to graphene, graphene oxide (GO) is readily disperse in aqueous electrolytes and can be reduced along with nickel and iron metal ions. While others had incorporated graphene in Ni-Fe deposits, no previous studies have addressed the role of GO particles on metal deposition. Ni-Fe is characterized by the anomalous codeposition behavior where there is a tendency of more Fe to be deposited than Ni even though there is an excess of Ni ions in the electrolyte. This behavior has been modeled assuming adsorbed intermediates. Here, the influence of GO on the deposit composition, structure and anomalous codeposition effect is investigated. The deposits were galvanostatically electrodeposited from a boric acid-sulfamate electrolyte at pH 2 containing commercial graphene oxide platelets. Two different cell configurations were examined:1) a rotating cylinder electrode (RCE) and 2) a copper mesh. The rotating cylinder as a working electrode was used in order to investigate mass transport. The copper mesh working electrode was placed in close contact to a flat bottom pH probe in order to examine the local pH change. The addition of GO to the electrolyte had an effect on the deposit composition and the local pH change (Fig 1). The deposit composition had either more Ni or remained the same compared to an electrolyte without GO on the RCE electrode at electrode rotation rates of 372 and 1000 rpm (Fig 1 (a) and (b)). The larger Ni content in the deposit was due to an enhanced Ni partial current density in the presence of GO. The local pH during the deposition on the mesh electrode with vigorous electrolyte stirring increased the local pH (Fig 1(c)). The composition behavior is similar to the results from the RCEs, with higher Ni content in the presence of GO. The local pH increase when GO was present is considered a factor that drives the enhanced Ni content, that may be a consequence of changes in adsorbed hydrogen. GO was not incorporated into the deposit; however, it had a dramatic effect on the morphology. There was less micro-cracks when GO was present in the electrolyte suggesting less adsorbed hydrogen. Thus, GO influenced the adsorbed intermediates making the electrodeposition less anomalous and having less cracks. Acknowledgement: This work was supported in part by the AESF Foundation. Figure 1. The influence of GO in the electrolyte during Ni-Fe electrodeposition (a) composition on a RCE, rotating rate (a) 372, (b)1000 rpm and (c) local pH measurements on a mesh electrode under vigorous stirring, 30 mA/cm2. Figure 1

High‐efficient electrocatalytic CO2 reduction to HCOOH coupling with 5‐hydroxymethylfurfural oxidation using flow cell

AbstractAmong various products from electrocatalytic CO2 reduction (CO2ER), HCOOH is highly profitable one. However, the slow kinetics of anodic oxygen evolution reaction lowers overall energy efficiency, which can be replaced by an electro‐oxidation reaction with low thermodynamic potential and fast kinetics. Herein, we report an electrolysis system coupling CO2ER with 5‐hydroxymethylfurfural oxidation reaction (HMFOR). A BiOCl–CuO catalyst was designed to sustain CO2ER to HCOOH at partial current density of 500 mA/cm2 with FEHCOOH above 90% and 700 mA/cm2 with FEHCOOH above 80%. In situ and ex situ x‐ray absorption fine structure was used to capture the structure transform of BiOCl–CuO into metallic Bi and Cu during CO2ER process, and the presence of CuO will promote this transformation which are supported by DFT calculations. Coupling HMFOR with CO2ER, we realize both FEHCOOH and FEFDCA above 95% simultaneously, providing new prospects vista for the electrosynthesis of value‐added products from paired system.

Enhanced CO2 Adsorption and Conversion in Diethanolamine‐Cu Interfaces Achieving Stable Neutral Ethylene Electrosynthesis

AbstractMolecular modifications have shown tremendous potential in boosting the electrochemical CO2 reduction (CO2RR) to ethylene. However, the key mechanisms of modulation at the molecular level remain unclear, especially for the adsorption and activation of key intermediates (e.g., *CO2 and *CO). Here, report that a diethanolamine (DEA)‐modified Cu catalyst can reduce CO2 to ethylene with a faradaic efficiency of ≈50.5% with a partial current density of ≈155.7 mA cm−2 in the neutral conditions, which surpasses the Cu catalyst without molecular modification (≈28.5% and ≈95.6 mA cm−2). Density functional theory calculations demonstrate that DEA on the Cu surface boosts the adsorption and activation of CO2 and the following C–C coupling processes during the CO2RR‐to‐ethylene process. Molecular dynamics simulations suggest that the molecules distant from the Cu site have a CO2 enrichment effect. Operational stability achieved via the introduction of DEA molecules onto ketjen black, which then successively immobilized on the Cu nanoparticles and polytetrafluoroethylene electrodes to obtain a stable tripe‐phase boundary, realizing constant ethylene selectivity for 100 operating hours in a flow cell.

Quantitative Analysis and Manipulation of Alkali Metal Cations at the Cathode Surface in Membrane Electrode Assembly Electrolyzers for CO2 Reduction Reactions.

The stable operation of the CO2 reduction reaction (CO2RR) in membrane electrode assembly (MEA) electrolyzers is known to be hindered by the accumulation of bicarbonate salt, which are derived from alkali metal cations in anolytes, on the cathode side. In this study, we conducted a quantitative evaluation of the correlation between the CO2RR activity and the transported alkali metal cations in MEA electrolyzers. As a result, although the presence of transported alkali metal cations on the cathode surface significantly contributes to the generation of C2+ compounds, the rate of K+ ion transport did not match the selectivity of C2+, suggesting that a continuous supply of high amount of K+ to the cathode surface is not required for C2+ formation. Based on these findings, we achieved a faradaic efficiency (FE) and a partial current density for C2+ of 77 % and 230 mA cm-2, respectively, even after switching the anode solution from 0.1 M KHCO3 to a dilute K+ solution (<7 mM). These values were almost identical to those when 0.1 M KHCO3 was continuously supplied. Based on this insight, we successfully improved the durability of the system against salt precipitation by intermittently supplying concentrated KHCO3, compared with the continuous supply.

Highly Selective Production of C2+ Oxygenates from CO2 in Strongly Acidic Condition by Rough Ag-Cu Electrocatalyst.

The acidic electrocatalytic conversion of CO2 to multi-carbon (C2+) oxygenates is of great importance in view of enhancing carbon utilization efficiency and generating products with high energy densities, but suffering from low selectivity and activity. Herein, we synthesized Ag-Cu alloy catalyst with highly rough surface, by which the selectivity to C2+ oxygenates can be greatly improved. In a strongly acidic condition (pH=0.75), the maximum C2+ products Faradaic efficiency (FE) and C2+ oxygenates FE reach 80.4 % and 56.5 % at -1.9 V versus reversible hydrogen electrode, respectively, with a ratio of FEC2+ oxygenates to FEethylene up to 2.36. At this condition, the C2+ oxygenates partial current density is as high as 480 mA cm-2. The in situ spectra, control experiments and theoretical calculations indicate that the high generation of C2+ oxygenates over the catalyst originates from its large surface roughness and Ag alloying.

High performance DC-TENG based on coupling of mismatched number of triboelectric units and electrodes with mechanical switches for metal surface anti-corrosion

Triboelectric nanogenerator (TENG) have proven to be a promising technology for harvesting dispersed mechanical energy. However, traditional TENGs based on triboelectrification and electrostatic induction generate electricity in alternating current (AC) mode, which needs to be converted into direct current (DC) for most applications. Here, we propose a DC-TENG based on the coupling of mismatched number of triboelectric units and electrodes with a mechanical switch design. This design not only simplifies the structure compared with previous multi-phase TENG and minimizes power loss, but enables a stable DC generation without post-management, which can be used directly to metal surface anti-corrosion. The experimental results show that the output current of this TENG with the mismatched number of triboelectric units (T) and electrodes (E) in 2T3E, 4T5E and 6T7E increases from 16.96 μA to 32.46 μA, achieving maximum power density of 33.20 mW with an external resistance of 80 MΩ. This enhancement in performance illustrates the effectiveness of the proposed design for harvesting and converting energy efficiently. Furthermore, the application of the mismatched MTE-TENG as a power source for metal surface anti-corrosion is explored. Through immersion experiments and electrochemical tests, the corrosion current decreases from 29.59 μA to 3.15 μA compared with bare carbon steel, which significant decreases in both anodic and cathodic branch currents, indicating the achievement of the anti-corrosion effect. This work provides a new way to achieve high DC output for metal surface anti-corrosion and realizes a green electrochemical anticorrosion process.

Molecular Engineering of Porous Fe-N-C Catalyst with Sulfur Incorporation for Boosting CO2 Reduction and Zn-CO2 Battery.

Transition metal-nitrogen-carbon (M-N-C) catalysts have emerged as promising candidates for electrocatalytic CO2 reduction reaction (CO2RR) due to their uniform active sites and high atomic utilization rate. However, poor efficiency at low overpotentials and unclear reaction mechanisms limit the application of M-N-C catalysts. In this study, Fe-N-C catalysts are developed by incorporating S atoms onto ordered hierarchical porous carbon substrates with a molecular iron thiophenoporphyrin. The well-prepared FeSNC catalyst exhibits superior CO2RR activity and stability, attributes to an optimized electronic environment, and enhances the adsorption of reaction intermediates. It displays the highest CO selectivity of 94.0% at -0.58V (versus the reversible hydrogen electrode (RHE)) and achieves the highest partial current density of 13.64mA cm-2 at -0.88V. Furthermore, when employed as the cathode in a Zn-CO2 battery, FeSNC achieves a high-power density of 1.19mW cm-2 and stable charge-discharge cycles. Density functional theory calculations demonstrate that the incorporation of S atoms into the hierarchical porous carbon substrate led to the iron center becoming more electron-rich, consequently improving the adsorption of the crucial reaction intermediate *COOH. This study underscores the significance of hierarchical porous structures and heteroatom doping for advancing electrocatalytic CO2RR and energy storage technologies.

Characterization of wine polyphenols with a carbon/nanoparticle TiO2 electrode

The positive effects of polyphenolic compounds on the sensory characteristics of wine and human health indicate a great need for a simple, fast and easily accessible method to determine the content of polyphenols in wine. The aim of this study is the electrochemical characterization of polyphenolic compounds in natural wine samples using a modified carbon paste electrode with TiO2 nanoparticles (MCPE/npTiO2) and improved voltammo­gram processing to obtain indicative data for polyphenols. The most marked influence of the modification of CPE with TiO2 nanoparticles was an increased sensitivity to electrooxi­dation, which is reflected in an increase of the anodic peak current. Of the five tested poly­phenols, i.e., gallic acid (GA), caffeic acid (CA), catechin (CT), quercetin (QV) and resveratrol (RE), the current maximum of the first two oxidation peaks increased only for GA by a factor of about 2 and for CT by a factor of about 1.5. Of the three red wines, Vranac (VR), Merlot (ME), Cabernet Sauvignon (CS); three white wines, Graševina (GR), Temjanika (TE), Char­donnay (CS) and one rose wine, Belrose Mediterranée Rosé (RO) tested, an increase by a factor of about 2.5 was observed for two red wines (VR, CS) and by a factor of 1.5 for one red wine (ME), one white wine (GR), and the rose wine (RO), while no increase in the current signal was observed for one of the white wines (CS). The most significant increase in the voltam­metric signal of GA at the MCPE/npTiO2 compared to other studied polyphenols can be explained by its higher affinity for adsorption on TiO2 nanoparticles. The investigated modified electrode provides an improved, linear and reproducible voltammetric response in wine samples. Consequently, MCPE/npTiO2 represents a good basis for the further deve­lopment of an integrated sensor/data system with the possibility of a broader application for the detection of polyphenols, especially GA, as an aroma and visually relevant parameter in winemaking.

Enhancing CO2 reduction with formamide-Ni@TiO2 catalyst

Formamide condensation with Ni can generate the NC structure, widely recognized as an efficient catalyst for electrocatalytic CO2 reduction reaction (CO2RR). To improve the utilization efficiency of Ni atoms, we introduced metal oxides as substrates to modulate the growth of a formamide-Ni (FA-Ni) condensate. FA-Ni@TiO2 demonstrated 2.8 times higher partial CO current density and Ni turnover frequency than FA-Ni, which were also higher than those of other FA-Ni@metal oxides, including ZrO2, Al2O3, Fe2O3, and ZnO. The improved performance of CO2RR can be attributed to the Ni content exposed on FA-Ni@TiO2 being twice that of the raw FA-Ni condensate. The Fourier transform infrared results suggested that formamide was adsorbed on TiO2 via the -CHO group, exposing -NH2 for potential interaction with Ni. As a result, Ni atoms were predispersed on the TiO2 surface. By contrast, the dispersion of Ni atoms was not enhanced by other metal oxides, such as Al2O3, Fe2O3, and ZnO, owing to the robust acidity of their surface sites. These metal oxides adsorbed formamide via -NH2, leading to the absence of extra -NH2 available for binding to Ni atoms. This study provides new insights into the development of appropriate substrates for single-atom catalysts.