Free Catalyst Research Articles

Functional graphitic carbon nitride/hydroxyapatite heterojunction for robust formaldehyde removal at ambient temperature

Ambient-temperature catalytic removal of formaldehyde (HCHO) hazard has been currently reckoned as a practicable and promising approach for abating indoor HCHO which severely haunts the human’s health. Catalyst with high-effectiveness and low-cost is a pivotal parameter determining the reliability and availability of this strategy. Herein, bifunctional graphitic carbon nitride/hydroxyapatite heterostructures (g-C3N4/HAP) were developed for indoor HCHO removal at ambient temperature. The optimal catalyst (g-C3N4/HAP-20) displayed enhanced HCHO removal efficiency of 36.6% and conversion (into CO2) efficiency of 28.4% within 2 h, compared with g-C3N4 (18.0% and 24.0%) and HAP (36.2% and ∼ 0%). Indoor fluorescent light accelerated HCHO elimination and its subsequent decomposition into CO2 over g-C3N4/HAP-20, delivering a HCHO removal efficiency of 82.7% and conversion efficiency of 100% within 2 h. Various characterizations and theoretical calculation reveal that g-C3N4/HAP possessed superoxide radicals and unpair electrons which were responsible for HCHO removal at ambient temperature; and a S-scheme heterostructure remarkably benefited the charge transfer and the photogenerated carriers’ separation, and consequently upgraded HCHO catalytic oxidation under indoor fluorescent-light illumination. This work offers a potent way to construct noble-metal free advanced catalysts with multi-functionality for indoor pollutant purification.

Air activation enhances the porosity and N,O synergistic effect towards an efficient metal free carbon cathode for Li-O2 battery

The achievement of Li-O2 batteries with high energy density and extended cycle life is often hindered by the disorderly growth of solid discharge product Li2O2 on the cathode and its sluggish decomposition reaction kinetics. Herein, under the guidance of DFT simulations, the N,O co-doped carbon was identified as a potential efficient metal free cathode catalyst to remit these problem in Li-O2 batteries. Then, a spherical shell-like N,O co-doped carbon was prepared through the direct pyrolysis of guanosine 5′-monophosphate disodium salt (5′-GMP, 2Na). After a further activation process in air, the carbon shells exhibit a finer porous surface with greatly enhanced specific surface area and surface N,O contents. As a result, the morphology of Li2O2 changed from large toroidal to film by using the activated carbon as a cathode catalyst due to its tailored surface structure with improved N and O synergistic effect. What's more, the film-like Li2O2 with Li vacancy can not only form an increased interfacial contact and interaction with the active sites on carbon, but also be conducive to the transfer of Li+/electrons during the decomposition of Li2O2, thus accelerating the electrochemical performances of the battery.

Bypassing Formation of Oxide Intermediate via Chemical Vapor Deposition for the Synthesis of an Mn-N-C Catalyst with Improved ORR Activity.

A significant barrier to the commercialization of proton exchange membrane fuel cells (PEMFCs) is the high cost of the platinum-based oxygen reduction reaction (ORR) cathode electrocatalysts. One viable solution is to replace platinum with a platinum-group metal (PGM) free catalyst with comparable activity and durability. However, PGM-free catalyst development is burdened by a lack of understanding of the active site formation mechanism during the requisite high-temperature synthesis step, thus making rational catalyst design challenging. Herein we demonstrate in-temperature X-ray absorption spectroscopy (XAS) to unravel the mechanism of site evolution during pyrolysis for a manganese-based catalyst. We show the transformation from an initial state of manganese oxides (MnOx) at room temperature, to the emergence of manganese-nitrogen (MnN4) site beginning at 750 °C, with its continued evolution up to the maximum temperature of 1000 °C. The competition between the MnOx and MnN4 is identified as the primary factor governing the formation of MnN4 sites during pyrolysis. This knowledge led us to use a chemical vapor deposition (CVD) method to produce MnN4 sites to bypass the evolution route involving the MnOx intermediates. The Mn-N-C catalyst synthesized via CVD shows improved ORR activity over the Mn-N-C synthesized via traditional synthesis by the pyrolysis of a mixture of Mn, N, and C precursors.

Effect of Fe–N–Cs as Catalytic Active Support for Platinum towards ORR in Acidic Environment

Metal-nitrogen-carbon (M–N–C) compounds such as Fe–N–Cs are currently the most promising platinum group metal free catalysts for oxygen reduction in acidic environment. Regarding the overriding goal of reducing PEMFC production costs by reducing the platinum content, the use of Fe–N–Cs as catalytic active support for low Pt amounts is investigated in this study. Activity and stability of Pt in different contents on a commercial Fe–N–C is compared to Pt on a typical carbon black. Pt nanoparticles are well-distributed on both support substrate classes. Although the electrochemical surface and mass activity of Pt is lower on Fe–N–C compared to carbon black, the Fe–N–C has a contribution to total ORR activity depending on the Pt/Fe–N–C ratio, which is quantified. In the low Pt content case of 1 wt%, the ORR activity is increased by factor of two in presence of Fe–N–C. This boosting effect on ORR activity is important for future strategies to lower the Pt content in PEMFCs.

Green synthesis of 2-trifluoromethyl quinoline derivatives under metal-free conditions and their antifungal properties

The skeleton of 2-trifluoromethyl quinoline is the core structure of many natural products and pharmaceutical molecules. The synthesis of this scaffold is limited by metal catalysis, harsh conditions, toxic or hazardous reagents and solvents, and lower atom-economy. Herein, a novel method for the synthesis of 2-trifluoromethyl quinolines via the [4 + 2] cyclization of β-keto esters or 1,3-diketones with various substituted o-aminobenzaldehydes using the metal free catalyst in EtOH is reported. This atom- and step-economical protocol features simple operation, broad substrate scope, and good functional-group compatibility. The synthetic utility of this methodology was highlighted by easy gram-scale synthesis and late-stage functionalization, which would promote the vigorous development of quinoline chemistry. Moreover, the in vitro antifungal activities of the 2-trifluoromethyl quinolines against F. graminearum (from wheat), F. graminearum (from corn), F. moniliforme, F. oxysporum, and R. solani were investigated to further potential utility of these compounds.

Highly active, ultra-low loading single-atom iron catalysts for catalytic transfer hydrogenation

Highly effective and selective noble metal-free catalysts attract significant attention. Here, a single-atom iron catalyst is fabricated by saturated adsorption of trace iron onto zeolitic imidazolate framework-8 (ZIF-8) followed by pyrolysis. Its performance toward catalytic transfer hydrogenation of furfural is comparable to state-of-the-art catalysts and up to four orders higher than other Fe catalysts. Isotopic labeling experiments demonstrate an intermolecular hydride transfer mechanism. First principles simulations, spectroscopic calculations and experiments, and kinetic correlations reveal that the synthesis creates pyrrolic Fe(II)-plN3 as the active center whose flexibility manifested by being pulled out of the plane, enabled by defects, is crucial for collocating the reagents and allowing the chemistry to proceed. The catalyst catalyzes chemoselectively several substrates and possesses a unique trait whereby the chemistry is hindered for more acidic substrates than the hydrogen donors. This work paves the way toward noble-metal free single-atom catalysts for important chemical reactions.

Toward practical applications in proton exchange membrane fuel cells with gram-scale PGM-free catalysts

Platinum has been considered as an essential element in both the cathode and anode catalyst in Proton Exchange Membrane Fuel Cells (PEMFC). However, with the increasing capacity of PEMFC industry in both transportation and stationary applications, the demand for platinum increases rapidly. From the standpoint of scarcity and cost, developing platinum group metal free (PGM-free) catalyst is rewarding. In this work, we prepared highly active material with secondary nitrogen doping, and were able to scale up material synthesis from milligram scale to gram scale with the high activity well maintained. The scale up catalyst SU-PAU was evaluated in 50 cm2 MEAs with comprehensive operating and design parameter optimization. The state of art 670 mW/cm2 peak power density was achieved under H2-Air operation, with the air partial pressure of 1 bar.

Highly durable platinum group metal-free catalyst fiber cathode MEAs for proton exchange membrane fuel cells

Fe-based platinum group metal (PGM)-free catalysts were incorporated into electrospun fiber mat or powder cathode membrane-electrode-assemblies (MEAs) with a Nafion 211 membrane and a Pt/C powder anode. Fabrication and characterization tests were performed on MEAs with: (1) a conventional powder cathode with a neat Nafion binder, (2) a fiber mat cathode with a Nafion/polyethylene oxide (PEO) binder, where PEO was extracted before MEA testing, (3) a powder cathode with a blended binder of Nafion and polyvinylidene fluoride (PVDF), and (4) a series of fiber mat cathodes with different Nafion/PVDF binder weight ratios. Cathode degradation occurred, with a loss in power output, in MEAs with a neat Nafion powder cathode or with a Nafion fiber cathode. In contrast, little or no power loss was observed for powder or fiber cathodes when the binder was a blend of Nafion and PVDF. The presence of hydrophobic PVDF drove water and electrogenerated peroxide out of the cathode, away from catalyst particles, which improved cathode durability, but PVDF also decreased the binder conductivity and slowed oxygen reduction kinetics, resulting in lower power densities. A 75:25 w:w Nafion:PVDF fiber cathode MEA was the best compromise for maximizing power and minimizing catalyst degradation. For such a cathode, with a PGM-free cathode catalyst loading of 3.0 mg cm−2, a power density of 88 mW cm−2 at 0.5 V, 80 °C, and 200 kPaabs pressure was maintained for 80 h of continuous operation.

Non-PGM Cathode Electrocatalysts for PEM Fuel Cells

The replacement of unsustainable noble-metal catalysts with platinum group metal (PGM)-free catalysts for oxygen reduction reaction (ORR) is essential for material wise and market value viable PEMFCs. Despite the tremendous efforts involved in their development, many drawbacks persist that include poor design of the architecture and chemical composition, control over the synthesis and poor stability, which seriously degrades their performance. These challenges are universally recognized and lead to a strong focus on designing alternative catalysts. Among the investigated candidates, Me–N-C catalysts are the most promising. In this work, the synthesis, characterization and evaluation of several Fe–N–C materials are presented. The synthetic approach involves templating using silicon-based materials. Structural, physicochemical, and electrochemical characterization in terms of ORR activity is also performed.

Greener Approaches Towards 1,4–Benzothiazine Synthesis: Recent Updates and Outlook

Abstract: Heterocyclic moieties are ubiquitous in nature and the exploration of heterocyclic chemistry goes centuries back, which have coalesced into the invention of greener methodologies towards the synthesis of heterocycles of potential uses. Benzothiazine is an important class of heterocyclic molecule, in which a benzene ring is fused with a six–member N, S containing ring. Amongst the three possible isomers, 1,4–benzothiazines show a wide spectrum of pharmaceutical and biological activities like anti–inflammatory, anti–rheumatic, antihypertensive, andantipathogenic roles. In search of greener protocols,metal–free catalysts, and environmentally benign reaction conditions, a lot have been unboxed to date, and many other dimensions remain yet to be deciphered. This minireview is an attempt to classify various sustainable protocols for the synthesis of 1,4–benzothiazine scaffolds over the last decade based on the reacting components and pathways, along with the consideration of plausible mechanistic insights and critical analysis.

N2 Activation and Reduction on Graphdiyne Supported Single, Double, and Triple boron Atom Catalysts: A First Principles Investigation.

AbstractFirst principles simulations were carried to investigate the activity and selectivity of single, double, and triple boron atom catalysts supported on graphdiyne (GDY) monolayer for N2 capture and reduction. Our results demonstrate that the double and triple boron atom catalysts bind and activate N2 molecule effectively with significantly large binding energies of 1.23 and 1.16 eV respectively. In depth density of states analysis revealed that build‐up of boron p states near the Fermi level promotes the N2 binding on the double and triple boron atom catalysts leading to strong overlap between boron and nitrogen p‐states. The free energy pathways for nitrogen reduction indicate very low limiting potentials of −0.41 and −0.58 V for the single and triple boron atom catalysts along the alternating pathways whereas the double boron atom catalyst is found to show a very high limiting potential of −3.29 V along the enzymatic pathway. Moreover, as compared to the single boron atom catalyst, the triple boron atom catalyst is found to be effective in suppressing the competitive hydrogen evolution reaction. Thus, we expect that the current work will lead to more investigation for design of transition‐metal free catalysts for N2 conversion to ammonia.

Boron-Activating Ruthenium from Organic-Free Synthesis Process: A Hydrogen Oxidation Reaction Catalyst for Anion Exchange Membrane Fuel Cells

Using fossil fuels, power generation is always accompanied by environmental pollution. However, hydrogen-oxygen fuel cells, using H2 generated from renewable energy, can provide electricity with zero emissions, meeting the significant demands. Proton exchange membrane fuel cells (PEMFCs), though commercialized, are hindered by the high cost due to relying on expensive Pt. By contrast, as the potential alternative, anion exchange membrane fuel cells (AEMFCs), have attracted more and more attention as they can provide the benefit of using low-cost cathode catalysts while still having high power density. Although the oxygen reduction reaction (ORR) on the cathode can be well achieved by platinum group metal (PGM)-free catalysts in an alkaline environment, the high loading of Pt for the anode is still needed for high power output caused by the sluggish hydrogen oxidation reaction (HOR) kinetics. As the cheapest PGM, Ru with lower HOR activity is often added as an activity promoter to reduce the Pt loading. Recently, more efforts have been put into using exclusively Ru as the main catalysis active site, but the synthesis methods are often complex and involve toxic organics.In this project, boron-activated Ru supported on carbon was developed for HOR catalysis in alkaline media. The B-Ru/C was synthesized by a simple organic-free method, making it possibly attractive for industrial application. This method adopted water as the only solvent and boric acid as the boron source to avoid the toxic problem and the tedious removal step of organics. It produced uniformly dispersed Ru nanoparticles in smaller particle sizes with a boron-rich environment verified by TEM and STEM images. Compared to Ru/C or Ru/BC, B-Ru/C not only has a higher electrochemical active surface area (ECSA) but also reached a much higher ECSA-normalized exchange current density which means boron does promote the activity of Ru. From the XPS spectra, the more significant peak shifts of Ru3p and B1s in B-Ru/C relative to Ru/C and BC indicate that the boron-ruthenium interaction is more robust in B-Ru/C than in Ru/BC. A theoretical simulation was conducted further to understand the mechanism of the HOR activity enhancement. From an electrochemical perspective, the B-Ru/C had a very high exchange current density in ex-situ tests and was also studied as an anode in operating AEMFCs. We believe this cost-effective Pt-free HOR catalyst with excellent performance prepared through an organic-free process can contribute to the industrial application of AEMFCs in the future.AcknowledgmentsThis work is supported by the Research Grant Council (HKUST C6011-20G).

High-Temperature “Ex-Situ” Cyclic Voltammetry to Study the Oxygen Reduction Reaction on Electrocatalysts in Conditions Mimicking Fuel Cell Operation

The massive efforts dedicated over the last decades to the development of improved electrocatalysts (ECs) and membrane-electrode assemblies (MEAs) have already yielded a significant reduction of the loading of platinum needed to devise low-temperature fuel cells (LT-FCs) achieving the performance and durability level that is required for applications. However, more research is still needed to further curtail the amount of Pt in a LT-FC; this is particular relevant to prevent supply bottlenecks in the perspective of a large-scale rollout of this technology.In a conventional LT-FC running on direct hydrogen most of the Pt loading is concentrated on the cathode electrode, where it is needed to promote the sluggish oxygen reduction reaction (ORR). It is often very time-consuming to optimize the features of a MEA to maximize its performance in a LT-FC running in operating conditions. This is especially the case if the MEA mounts innovative ORR ECs exhibiting features that are very different from benchmark ECs in terms of chemical composition of the active sites and morphology. Thus, the general practice is to screen developmental ORR ECs through “ex-situ” techniques before focusing MEA optimization only on the most promising systems.The most widespread “ex-situ” approach to screen developmental ORR ECs involves the use of a rotating (ring) disk electrode (R(R)DE) setup. Though very practical and accurate, conventional R(R)DE experiments are able to study the ORR features of an EC only in quite a narrow set of operating conditions (T = 30-60°C; P = 1 bar). These latter are different from those that are most commonly adopted at the cathode of a LT-FC (T = 80-100°C; P = 2 – 3 bar). As a result, the information obtained on the ORR features of an EC by means of conventional R(R)DE studies may not be fully representative of the behavior of the EC in an operating LT-FC.To address this shortcoming herein we present an innovative setup able to elucidate the ORR features of both benchmark and innovative ECs in experimental conditions that are very close to those found in operating low-temperature FCs. Specifically, the setup consists of a homemade channel flow electrode (CFE) cell operated in a rather simple closed system with a controlled oxygen concentration and maintaining a high level of cleanliness.The modeling, materials selection, design, and testing of a versatile CFE cell developed from scratch is presented. The cell is compatible with commercially-available RDE components and special care is devoted to ease the overall assembly of the experimental setup. The cell is characterized by a well-defined hydrodynamics, a low dead volume, a high mass-transfer rate and a high signal/noise ratio. The cell also allows to measure accurately the pressure and the temperature in close proximity of the working electrode. It is demonstrated the possibility to study the ORR features of ECs up to a temperature of 80°C and a pressure of 3 bar. Both benchmark and innovative ECs are taken into consideration. The latter exhibit features that are very different in comparison with the conventional Pt/C ECs, especially in terms of: (i) chemical composition of the active sites, that typically includes more than one element; and (ii) morphology of the support, that is based on different carbon nanostructures. The proposed setup is implemented to determine crucial ORR features of the ECs, including the kinetically-controlled current, the activation energy and the accessibility of O2 to the active sites. Acknowledgements This research has received funding from: (a) the European Union’s Horizon 2020 research and innovation program under grant agreement 881603; (b) the project ‘Advanced Low-Platinum hierarchical Electrocatalysts for low-T fuel cells’ funded by EIT Raw Materials; (c) Alkaline membranes and (platinum group metals)-free catalysts enabling innovative, open electrochemical devices for energy storage and conversion – AMPERE, FISR 2019 project funded by the Italian Ministry of University and Research; and (d) the German Federal Ministry of Education and Research (BMBF) under grant agreement number 03SF0585.

(Invited) Carbon-6 Based Sustainable Value Chains Towards Specialties and (Aviation) Fuels Based on Low-Temperature PEM-Water Electrolysis and Syngas Fermentation

Sustainable value chains by coupling electrolysis and fermentation The energy transition also needs a raw material transition. The process sequence of water electrolysis and syngas fermentation was found to provide access to C4-C6 based value chains based on CO2 and H2. In the German Kopernikus and Rheticus projects Siemens Energy Global GmbH & Co. KG (SE) and Evonik Operations GmbH focused on a sustainable synthesis of C6 oxygenates for specialty chemicals, food additives and even fuels1,2. Routes to kerosene exist. The technology was successfully implemented in chemical plant environment at Marl with an annual production capacity of ~15t. The scaling into the multimillion-ton annual production range depends on various boundary conditions, such as the availability of renewable energy at competitive cost, the political situation as well as its customer acceptance. Silyzer 300 PEM electrolysis SE is one of the key companies willing to implement the German National Hydrogen Strategy3 until 2030. The current product is named Silyzer 300® with 17,5 MW rated power at begin of life on system level4. The stack core consists of a non-pressurized array with 24 modules, producing around 335 kg of hydrogen per hour. SE is investing more than 60 Mio.€ for the massive ramp-up of electrolyzer production capacity through automation5. Series production (SEGIWA) and de-risking, qualification for large-scale application (= de-risking; DERIEL) are funded within the H2Giga program6. Perspectives in AEM-Membranes Anion Conducting Membranes offer design and operation options in polymer membrane water electrolysis. Electrochemical data from the project AEMready will be presented with respect to noble metal free catalysts and choices of membranes. Acknowledgement The investigations reported on the value chain was partly funded by the BMBF under the contract numbers Kopernikus I & II (FKZ: 03SFK2J0-2), Rheticus I & II (FKZ: 03SF0574B). Scaling is BMBF-supported by the H2Giga initiative within the projects SEGIWA (FKZ: 03HY121A) and DERIEL (FKZ: 03HY122A). AEM activities are funded by AEMready (FKZ:03SF0613B). References Haas, R. Krause, R. Weber, M. Demler, G. Schmid, Nature Catalysis, 2018, 1, 32–39.https://www.bmbf.de/de/fuer-eine-klimafreundliche-industrie-kohlendioxid-und-wasserstoff-als-rohstoffe-fuer-12543.html .https://www.bmwk.de/Redaktion/EN/Publikationen/Energie/the-national-hydrogen-strategy.pdf?__blob=publicationFile&v=6.https://www.siemens-energy.com/global/en/offerings/renewable-energy/hydrogen-solutions.html?gclid=EAIaIQobChMIsuu-wMHV-wIVktZ3Ch24ngoYEAAYASAAEgJUF_D_BwE.https://press.siemens-energy.com/global/en/pressrelease/new-production-facility-berlin-siemens-energy-wants-eliminate-worlds-most-potent .https://www.wasserstoff-leitprojekte.de/projects/h2giga .

Toward Understanding Interfacial Phenomena of Anion Exchange Membrane Water Electrolyzers: Investigating the Role of Electrolyte pH Gradient with Operando Raman Spectroscopy

There is growing industrial appeal of anion exchange membrane water electrolyzers (AEMWEs) to produce hydrogen. A significant challenge remains that AEMWE durability testing is not standardized, and more minute interfacial degradation mechanisms between ionomer, catalyst, membrane, and electrolyte are not well characterized. Of particular interest is the impact of electrolyte selection on the polarization performance. There is a general desire to achieve reliable operation with environmentally obtained saltwater as the electrolyte, although this presents numerous challenges manifesting in typically poor long-term durability. Saltwater presents complexities in determining electrolyzer component interfacial phenomena.Performance of AEMWEs is typically benchmarked with hydroxide or carbonate solutions, therefore providing more direct opportunities to study fundamental mechanisms with regards to interactions between surfaces. Of particular interest is the presence of electrolyte anion concentration gradients that depend on the polarization state of the oxygen evolution reaction electrode (OER). We demonstrated in our early work with operando Raman probing of a custom designed spectroelectrochemical cell that there is initial evidence of spatially resolved anion gradients from the OER electrode surface into bulk electrolyte in a half cell configuration. We hypothesize that local pH changes near an electrode surface may impact the polarization via transport limited ion exchange and the relative overpotential of the overall cell, ultimately leading to an iterative and long-term contribution to decaying cell durability.We continue our work with a series of in-situ Raman experiments with a full cell configuration: OER electrode with PGM free catalyst, hydrogen evolution reaction (HER) electrode with PGM free catalyst, and anion conductive polymer membrane. Both electrodes also contain an ionically conductive polymer, or ionomer, that serves as a binder. By increasing the complexity of the system to match that of an industrially relevant configuration, we aim to probe the spatially resolved pH gradient with both potassium hydroxide and potassium carbonate solutions of varying concentrations. We utilized a custom, 3D printed, flow cell design comprising a sapphire observation window and isolated electrolyte flow chambers.Operando Raman spectroscopy measurements were conducted primarily with potassium carbonate solutions by tracking the spatially resolved changes in relative peak intensity of carbonate and bicarbonate signatures. With regards to the carbonate-bicarbonate equilibrium, we calculate changes in pH as the probe approaches the surface of an electrode. We finally connect our findings to a proposed mechanism for the interfacial phenomena relative to cell durability as a function of concentration changes and operating voltages.

Design of Noble-Metal-Free Membrane Electrode Assemblies Based on Metal Chalcogenides for Electrochemical Hydrogen Production Via Alkaline Seawater Electrolysis

The production of large amounts of green hydrogen (H2) by electrochemical water splitting represents one of the key pillars to reach net-zero by 2050. As one of the major drawbacks, both low-temperature proton-exchange membrane (PEM) as well as anion-exchange membrane (AEM) electrolysis still rely on the utilization of noble metals in the catalyst layers driving the evolution of H2 and oxygen (O2) on the cathode (HER) and on the anode (OER), respectively. Beyond that, the requirement for highly pure water feeds to prevent degradation of the cell performance over time was previously addressed as one of the main concerns. In particular, this holds true for arid regions located close to the ocean. Advantageously, these coastal arid zones provide essentially unlimited access to seawater, coupled with ample solar irradiation and wind throughout the entire year.[1]One of the major challenges for direct seawater electrolysis lies in the development of selective catalysts, especially for the anode due to the inherently faster reaction kinetics of the competing two-electron chlorine evolution reaction (ClER). Nickel-iron layered double hydroxides (NiFe-LDH) were identified as active and selective OER electrocatalysts in a previous study[2] by our group. Dionigi et al.[3] recently reported a general design principle for selective seawater electrolysis, in which alkaline pH values > 7.5 are claimed to favor OER over ClER for overpotentials < 480 mV.At the cathode, state-of-the-art electrolyzers utilize Pt-based catalysts for an efficient HER.[2] For direct seawater electrolysis, however, not only the high cost but also the weak stability due to chloride-induced corrosion restrict the applicability of Pt-based electrodes. In our contribution, we thus present noble-metal free catalyst materials based on metal chalcogenides with high HER activity and improved stability in alkaline seawater electrolyte in a single-cell electrolyzer setup. Membrane-electrode assemblies (MEAs) with superior corrosion-resistance by a modification of the porous transport layers (PTLs) for both cathode and anode will be presented, which outperform reference MEAs containing Pt-based cathodes in alkaline seawater electrolysis. The optimized noble-metal-free electrode design (fig. 1) combined with well-controlled electrolyte feeding enables alkaline seawater electrolysis operating at industrially relevant current densities.

(Invited) Component Design and Electrode Optimization for AEM Electrolyzers

The massive international investment in water electrolysis has accelerated the need to reduce cost and increase durability. In recent years, Anion exchange membrane electrolyzers (AEMELs) have been touted as a possible low-cost option to supplant traditional alkaline electrolyzers and proton exchange membrane electrolyzers because they promise to combine the benefits of both – namely high current density operation, high discharge pressure, the use of noble-metal free catalysts, and the ability to use a wider range of materials for other cell components. As AEMELs are still early in their developmental stage, much of the reported work in the literature has dealt with the development of new catalysts or membranes for these devices and have worried less about engineering aspects of AEMEL design such as loading optimization, the structure and composition of the porous transport layers (PTL), the balance of IEC between the cathode, membrane and anode, etc. This presentation intends to take the audience through a systematic optimization of the anode and cathode electrodes for AEMELs. Some of the variables to be discussed are: i) IEC and cross-linker content of the ionomers; ii) ionomer physical structure; iii) catalyst loading; iv) PTL density and thickness; and v) number of layers that comprise the catalyst layer. The balance and sometimes compromise between performance and durability will also be discussed. By the end of the presentations of electrodes will be demonstrated that were integrated into AEMELs and are able to show very low voltage operation on both deionized water (1.9 V @ l.0 A/cm2) and 0.3 M KOH (1.65 V @ 1.0 A/cm2 and < 2 V @ 3.0 A/cm2) as well as stable operation for as much as 720 hours (30 days).

Co-based metal-organic frameworks confined N-hydroxyphthalimide for enhancing aerobic desulfurization of diesel fuels

N-hydroxyphthalimide (NHPI) is a powerful green nitrogen-containing free radical catalyst, while the leaching of homogeneous NHPI remains a crucial obstacle. Herein, the cobalt-based metal–organic frameworks (Co-based MOFs) were introduced as the supports and co-catalysts to successfully confine the NHPI catalyst. NH3-TPD characterization confirmed that the heterogeneous catalyst NHPI@Co-MOF containing carboxyl groups linker exhibits more assertive acidity, facilitating the activation of O2 to generate active radicals O2•− that determined the catalytic activity. Owing to these features, NHPI@Co-MOF-DA with two carboxyl groups as the linker achieved 98 % of DBT conversion at 120 °C. Moreover, the DBT conversion of the used catalyst reached 95 % after being recycled 10 times. The distinctive design strategy provided valuable insights into the selection of suitable organic linkers to enhance the synergistic effect of metal cobalt with NHPI in the oxidative desulfurization (ODS) process, broadening the research horizon of MOF hybrids in the construction of efficient ODS applications.

Highly Active NiO-Ni(OH)2 -Cr2 O3 /Ni Hydrogen Evolution Electrocatalyst through Synergistic Reaction Kinetics.

High activity catalysts for hydrogen evolution reaction (HER) play a key role in converting renewable electricity to storable hydrogen fuel. Great effort has been devoted to the search for noble metal free catalysts to make electrolysis viable for practical applications. Here, a non-precious metal oxide/metal catalyst with high intrinsic activity comparable to Pt/C was reported. The electrocatalyst consisting of NiO, Ni(OH)2 , Cr2 O3 , and Ni metal exhibits a low overpotential of 27, 103, and 153 mV at current densities of 10, 100, and 200 mA cm-2 , respectively, in a 1.0 m NaOH electrolyte. The activity is much higher than that of NiOx /Ni or Cr2 O3 alone, showing the synergistic effect of NiOx /Ni and Cr2 O3 on catalyzing HER. Density functional theory calculations shows that NiO and Cr2 O3 on Ni surface lower the disassociation energy barrier for breaking H-OH bond, while Ni(OH)2 and Cr2 O3 create preferred sites on Ni surface with near-zero H* adsorption free energy to promote H* to gaseous H2 evolution. These synergistic effects of multiple-oxides/metal composition enhance the disassociation of H-OH and the evolution of H* to gaseous H2 , thus achieving high activity and demonstrating a promising composition design for noble metal free catalyst.

Highly Porous Polypyrrole (PPy) Hydrogel Support for the Design of a Co-N-C Electrocatalyst for Oxygen Reduction Reaction.

Atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts have emerged as one of the most promising platinum-group metal (PGM)-free cathode catalysts for oxygen reduction reaction (ORR). Among the various approaches to enhance the ORR performance of the catalysts, increasing the density of accessible active sites is of paramount importance. Thus, nitrogen-rich support with abundant porosity can be very propitious. Herein, we report a highly porous polypyrrole (PPy) hydrogel as a versatile support for the facile design of a Co-N-C electrocatalyst for ORR. The resulting Co-N-C catalyst with abundant micro- and mesoporous combinations demonstrates a half-wave potential (E1/2) of 0.825 V vs reversible hydrogen electrode (RHE) in O2-saturated 0.1M KOH with just 2.1 wt % Co content. The ORR performance reduces only 11 mV (E1/2) after 5000 cycles of accelerated durability test (ADT), portraying its excellent stability. The catalyst retains ≈83% of its original current during a short-term durability test at 0.8 V vs RHE for 25 h. Furthermore, the catalyst shows electron transfer approaching ≈4 with low H2O2 yield in the potential range 0.5-0.9 V vs RHE. This work provides a simple design strategy to synthesize M-N-C catalysts with increased accessible active site density and enhanced mass transport for ORR and other electrocatalytic applications.