Noble Catalysts Research Articles

Low Temperature Thermal and Solar Heating Carbon‐Free Hydrogen Production from Ammonia Using Nickel Single Atom Catalysts

AbstractCatalytic splitting NH3 to H2 is one of the foundations for building a carbon‐free H2 energy system but requires NH3 splitting catalysts that are highly active and durable at low temperatures. Although various non‐noble catalysts have been designed, NH3 splitting still operates at relatively high temperatures (600–850 °C). Herein, theoretical calculations predict that the Ni single atoms can change the bonding mode of NiN from covalent bond to ionic bond to boost the NH3 splitting activity. Further, Ni single atoms supported on CeO2 nanosheets (SA Ni/CeO2) are synthesized by the sol–gel method, which exhibits a robust 3.544 mmol g−1 min−1 of H2 yield speed of NH3 splitting at 300 °C, superior to all non‐noble catalysts and most of the noble catalysts. Combing with the homemade solar heating device, the one sun‐driven NH3 splitting over SA Ni/CeO2 shows a stable H2 yield of 1.58 mmol g−1 min−1, 100 times the record value of advanced weak solar‐powered NH3 splitting, demonstrating the potential for practical application in carbon‐free H2 systems.

Understanding the growth N–Fe3C from assembly of carbon-coated iron nanoparticles on rGO as efficient oxygen reduction electrocatalysts

The oxygen reduction reaction (ORR) is an essential reaction in metal-air battery systems. However, the traditional noble metal Pt-based catalysts for ORR limit the commercial applications of air battery systems due to their high price, low abundance and poor tolerance. In recent studies, nitrogen–doped transition metal carbides have shown promise as an alternative to traditional noble metal catalysts. In this paper, the thermal cracking and calcination method was used to successfully obtain the growth N-doped carbon coated iron carbide nanoparticles (Fe3C@NC/rGOx NP) from assembly of carbon-coated iron oxide Nano-crystals on rGO (Fe3O4@NC/rGOx NCs). Transmission electron and scanning electron microscopy of the fabricated specimens indicated the presence of many carbon shells and pores in the etched samples. The electrochemical test results of the fabricated specimens suggested that the Fe3C@NC/rGO 100 NP annealed at 800 °C exhibited a better ORR behavior than that of Pt/C in a basic electrolyte.

Impact of gas treatment of CuAl-LDH on NO reduction by CO under oxidative conditions

Removal of NO from cement-type industrial flue gases can be achieved by its catalytic reduction with CO (NO-Selective Catalytic Reduction) over a suitable noble metal free catalyst. Cu-Al mixed metal oxides derived from parent Layer-Double Hydroxide (LDH) after thermal decomposition under different pre-treatment gas conditions: inert (He), oxidising (air), reducing gas (1 %CO in He) at 500 °C have been used to achieve it. Additionally, a mixed oxide was prepared by the treatment of the LDH under 100 % CO2 at 500 °C, a novel method for synthesis of mixed oxides is reported in this study. Different characterization techniques (N2-Physisorption, XRD, H2-TPR, TGA and FTIR) were used to investigate physico-chemical properties of CuAl mixed oxide materials to determine their role on the catalytic performances. It was observed that gas treatments did not affect the crystal size (∼20 nm) of the corresponding Cu-Al mixed oxide except for CO/He treatment, where highly crystalline phases of Cu(0) were formed predominantly instead of CuO as in other Cu-Al mixed oxide samples. Further, the catalytic tests were performed using a simulated industrial gas composition from a cement industry consisting of CO (0.13 vol%), CO2 (20 vol%), NO (475 ppm), O2 (8.8 vol%) and without or with H2O (8.2 vol%), the rest being balanced by He. Both NO reduction and oxidation reactions occurred in the presence of water over CuAl-CO/He, CuAl-He, CuAl-CO2 and CuAl-air samples. However, only CuAl-CO2 was the only sample active for the NO reduction (N2 selectivity was 83 %) in the absence of water in the reaction feed. Moreover, under wet reaction conditions, CuAl-CO2 sample showed similar catalytic activity like its CuAl-air and CuAl-He counterparts (NO reduction yield of 13–16 % at peak temperatures of 420–400 °C). The plausible formation of monodentate and/or bidentate carbonates onto the material during the CO2-treatment at 500 °C (inferred from TGA and FTIR measurements) was proposed to promote NO reduction activity in the absence of water while under wet conditions, these carbonate species supposedly reacted with the water species and formed in active formiate species. This resulted in a mixed oxide with material properties similar to that of the CuAl-air and CuAl-He samples and therefore, led to similar catalytic performance. Finally, our study showcased the effect of novel CO2 treatment for CuAl-LDH precursor in improving the performances for NO reduction.

Kinetic evaluation of perovskites-type catalysts in the reduction of 4-nitrophenol: A mechanistic elucidation study

• The effect of electron scavengers helps determine the type of surface mechanism in 4NP reduction. • 4NP reduction by borohydride is a surface catalytically driven reaction. • Perovskites, are alternatives to noble metal-containing heterogeneous catalysts for degradation of environmental pollutants. Herein, we report on the catalytic activity of ABO 3 perovskites (A = La or Sr, B = Co, Sn, Fe, or Al) synthesized by nanocasting technique with silica-based KIT-6 as a hard template. The physical and chemical characteristics of the perovskites were determined using various techniques such as powder X-ray diffraction, nitrogen sorption, transmission and scanning electron microscopes and temperature programmed desorption. The synthesized ABO 3 perovskites were used as heterogeneous catalysts in the reduction of 4-nitrophenol (4NP) by sodium borohydride (NaBH 4 ) to 4-aminophenol (4AP). The perovskites exhibit surface areas ranging from 19 to 101 m 2 /g. Among the as-synthesized perovskites SnAlO 3 was the most acidic catalyst and exhibited the highest catalytic activity towards 4NP reduction. We further explored the role of electron scavengers in elucidating the catalytic mechanism and postulate that the reduction of 4NP follows a surface-driven electron transfer mechanism.

Electrosynthesis of eco-friendly electrocatalyst based nickel-copper bimetallic nanoparticles supported on poly-phenylenediamine with highest current density and early ethanol oxidation onset potential

Bimetallic catalysts have been investigated as the most efficient materials to accelerate the chemical transformations at the anode in Direct Ethanol Fuel Cells. A comparative study is presented here to synthesize Ni–Cu bimetallic nanoparticles for the ethanol oxidation reaction on three conducting polymers: poly-ortho-phenylenediamine, poly-meta-phenylenediamine, and poly-para-phenylenediamine. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Electrochemical Impedance Spectroscopy (EIS) were used to analyze the modified electrodes. A series of bimetallic Ni–Cu nanoparticles with tunable ratios were successfully synthesized by simply changing the concentrations of Nickel and Copper. It has been confirmed that the best Ni/Cu molar ratio was 25% in the aspect of catalytic performance. The electrocatalyst exhibited an excellent catalytic activity with an anodic current of 70.5 mA cm−2 at the lowest onset potential of 0.39 V with impressive stability. Ni4Cu1/PpPD should be considered as a good alternative to noble metal anode catalyst.

Selective production of monocyclic aromatic hydrocarbon from agricultural waste wheat straw for aviation fuel using Ni/ZSM-5 catalyst

Aromatic is a vital chemical raw material and product as well as an essential component for aviation fuel. Bio-based aromatics, especially the monocyclic aromatic hydrocarbon, are beneficial for the green chemical process and aviation fuel development. In this research, firstly, the effects of different kinds of metal catalysts (Pt/C, Rh/C, Ru/C, Pd/C, 65 wt% Ni/SiO2–Al2O3) on the pyrolysis behavior and aromatic hydrocarbons selectivity of four kinds of agricultural and forestry waste biomass (wheat straw, rape straw, poplar sawdust, and bamboo powder) were systematically investigated. The research results showed that the selectivity of aromatics has been largely increased in the presence of 65 wt% Ni/SiO2–Al2O3 while the carbon-based noble catalysts had few impacts on aromatics production. Furtherly, zeolite with different Si/Al ratios (5:18, 5:50, 5:85, 5:300, and 5:470) and the Ni loading amounts (5, 10, 15, 20, 25 wt%) were systematically studied. The series of Ni/ZSM-5 catalyst reduced the phenolic components in the pyrolysis products, and significantly increased the relative content of the target product aromatics, and the proportion of monocyclic aromatic hydrocarbons in the aromatic. The research results showed the ZSM-5 with the Si/Al ratio of 5:18 had the best catalytic properties for aromatic production. The loading of 10 wt% of Ni (10 wt% Ni/ZSM-5, Si/Al = 5:18) further boosted the catalytic performance for wheat straw, achieving the highest relative concentration of aromatic at 67%, of which the ratio of monocyclic aromatic hydrocarbon was 55%.

Defects engineering of metal-organic framework immobilized Ni-La(OH)3 nanoparticles for enhanced hydrogen production

The development of low-cost, efficient, and durable catalysts to boost hydrogen production from hydrous hydrazine (N2H4·H2O) and hydrazine borane (N2H4BH3) is critical, but still a huge challenge. Herein, for the first time, noble-metal-free La(OH)3-doped Ni nanoparticles (NPs) supported on defect-rich metal−organic framework were constructed via a facile, green, and low-cost wet-chemical method. It is first found that the number of defects in MIL-125(Ti) can be easily regulated by a simple but efficient method. As a result, the defect-rich MIL-125-supported Ni-La(OH)3 catalyst shows superior catalytic activity, 100 % H2 selectivity, and robust durability for N2H4·H2O dehydrogenation with NaOH at 343 K, providing a turnover frequency (TOF) value high up to 870 h−1, surpassing all the non-noble metal catalysts reported so far and even outperforming some noble metal-containing catalysts. Interestingly, the catalyst also shows excellent catalytic efficiency for hydrogen production from N2H4BH3 with a TOF value as high as 2381 h−1 at 343 K. The superior catalytic efficiency is mainly due to the existence of abundant defective MIL-125, electron-rich, good dispersed and small Ni NPs, as well as the synergistic effect between metal and support. This work delivers inspiration in defect engineering and provides a promising strategy for rationally designing high-efficiency MOFs-based catalysts for hydrogen generation and other heterogeneous catalysis.

Sp-nitrogen and γ-ray modulating multiply γ-graphyne for anchoring Pt nanoparticles to boost oxygen reduction activity and stability

γ-Graphyne (GY) is a potential carbon support for anchoring platinum nanoparticles (Pt NPs) in oxygen reduction reaction (ORR). However, the high oxygen penetration barrier of primitive GY intercepts its application for ORR. Herein, based on the stronger negative charge density of sp-hybridized nitrogen (sp-N) atoms and the regulation of γ-ray irradiation on carbon nanostructure, a Pt/N50-GY catalyst with a multi-level pore structure, larger specific surface area (twice that of original GY) and more Pt NPs anchor sites was fabricated by sp-N doping and γ-ray irradiation, which reduced the oxygen penetration barrier of original GY, exposed more active sites, shortened ion migration path and accelerated mass transfer, thus improving the ORR performance. The ORR activity of Pt/N50-GY catalyst is superior to that of the commercial Pt/C and even more outstanding when compared with the mostly reported graphdiyne related and noble meal catalysts under lower catalyst loading. Additionally, the Pt/N50-GY catalyst showed superior stability to the commercial Pt/C. Our work breaks the bottleneck that GY can not be applied to ORR, and provides a breakthrough way for the application of GY in ORR.

Rhodium decorated stable platinum nickel nanowires for effective ethanol oxidation reaction

Direct ethanol fuel cells (DEFCs) are considered one of the most promising energy resources for portable power devices. The current mainstream catalysts used for DEFCs are Pt- or Pd-based, which facilitate the partial oxidation of ethanol to CH3CHO or CH3COOH, but not the C—C bond cleavage, which is the inevitable path for the complete oxidation of ethanol. In addition, most noble catalysts are easily poisoned by CO, shortening their lifespan and stability, thus inhibiting the practical application of the catalysts. Herein, we report a type of ultrathin trimetallic Pt/Ni/Rh nanowires with various Rh contents toward the ethanol oxidation reaction (EOR), and the optimized Pt6Ni2Rh3/C demonstrates a high mass activity of 1.16 A mgPt−1 as well as considerable stability, anti-CO poisoning ability, and complete ethanol oxidation selectivity. In addition, density functional theory calculations reveal that introducing Rh to bimetallic Pt/Ni endows the catalyst with a moderate intermediate adsorption capacity and enhanced C—C bond cleavage capacity, favorable for the complete oxidation of ethanol.

Effects of Artificial River Water on PEM Water Electrolysis Performance

Hydrogen, a clean and renewable energy source, is a promising substitute for fossil fuels. Electricity-driven water electrolysis is an attractive pathway for clean hydrogen production. Accordingly, the development of electrolysis cells has drawn researchers’ attention to capital costs related to noble catalyst reduction and membrane degradation by the contaminations. In the literature, polymer electrolyte membranes (PEMs) have been studied on single cations contamination. In this study, we investigated the performance of a PEM on monovalent and divalent cation contamination by feed water. Artificial river water, called soft water, was used to analyze the effect of impurities on the PEM. The results demonstrated that the operating voltage drastically increased and induced cell failure with increasing Mg2+ and Ca2+ concentrations; however, it did not increase for Na+ and K+ after increase in voltage. Therefore, divalent cations have a stronger affinity than monovalent cations to degrade PEM and should be effectively excluded from the feed water.

3D PdPb nanochain networks with efficient catalytic performance for ethylene glycol electrooxidation

The noble metal anodic catalysts with three-dimension (3D) chain-like network structure have been researched thoroughly due to their unique morphological characteristics. Herein, a novel scheme has been designed rationally to synthesize 3D PdPb nanochain networks (PdPb NCNs). Numerous nanochains were interlaced and stacked to form the nanonetworks, which were contributed to improving electrocatalytic performance. Abundant steps and kinks existed on the nanochain networks, which provided plentiful active sites to improve the electrocatalytic activity. In the subsequent electrochemical tests, the mass activity of Pd65Pb35 NCNs was 4.47 A mg pd−1, higher than other catalysts. Moreover, in the chronoamperometry and consecutive CV measurements, Pd65Pb35 NCNs exhibited the best stability than other prepared samples. This work explored the rational synthesis of PdPb nanochain networks, and confirmed the excellent electrocatalytic performance in EGOR.

Interface modulation of Pt/Al2O3 catalyst and their roles in thermal stability

Interfacial local environment of noble metal nanoparticles (NPs) and support is crucial for the development and design of thermally and chemically stable noble metal heterogeneous catalysts. The unique chemical environment can strengthen the NPs interaction with the support surface, which can effectively avoid the agglomeration of NPs. The strategy is developed to modulate the interfacial chemical environment of supported Pt NPs with the help of the unsaturated Al3+ in Al2O3N (nanobelt) support, resulting in a sintering-resistant Pt/Al2O3N catalyst. Al solid-state MAS NMR characterization shows that Al2O3N support contains a large amount of unsaturated Alpenta3+ (about 22.6%). XAS confirms that Pt NPs deposited on the surface of Al2O3 with rich unsaturated pentahedral coordinated Al3+ sites have a unique coordination structure at the interface (more Pt-O coordination). When catalyzing the CO oxidation as a probe reaction, the catalytic activity and the particle sizes of Pt NPs do not change significantly even after the reaction at 400 °C for 15 days, and the complete CO conversion temperature increases only by 40 °C when the catalyst is screened at 600 °C for 5 days. This work demonstrates a new strategy to develop stable large-scale anti-sintering noble metal-based heterogeneous catalysts for many important high-temperature industrial applications.

Tuning the Electronic Structure of Cobalt Selenide on Copper Foam by Introducing a Ni Buffer Layer for Highly Efficient Electrochemical Water Splitting.

The development of a cost-effective, remarkably competent, and durable bifunctional electrocatalyst is the foremost requirement of water splitting to generate H2 fuel as a renewable energy technology. Three-dimensional porous copper foam (Cuf) when electrochemically decorated with transition metal selenide results in a highly active electrocatalyst for adequate water electrolysis. In terms of water splitting, the role of cobalt selenide and Cuf has already proven to be remarkable. The introduction of a Ni buffer layer between Cuf and cobalt selenide (Cuf@Ni-CoSe2) acts as a valve to enhance the electron thrust from the substrate to the material surface with no compromise in the overall material conductivity, which not only increases the efficiency and activity but also improves the stability of the catalyst. The self-supported synthesized catalyst material showed an admirable activity toward the oxygen evolution reaction and hydrogen evolution reaction in alkaline media. The performance of the catalyst was found to be significantly better than that of the noble catalyst RuO2. The catalyst was very stable up to 93 h and attained a full cell voltage of only 1.52 V at a current density of 10 mA cm-2. Therefore, for large-scale hydrogen production, this as-synthesized catalyst hss the potential to replace conventional fossil fuel-based energy systems.

Hierarchically porous polyHIPEs fabricated via ex-situ swelling strategy towards supports for noble-metal Ag nanoparticles

This work demonstrates an ex-situ swelling strategy for fabrication of the robust hierarchically porous polyHIPE. Specially, a cationic polyHIPE was prepared by copolymerization of 2-(methacryloyloxy) ethyltrimethylammonium chloride, styrene and divinylbenzene within a water-in-oil (w/o) high internal phase emulsion (HIPE). The hierarchically porous polyHIPE was achieved via simply swelling the polyHIPE in decane at 70 °C, and subsequent removal of the solvent at room temperature. There were large amounts of small pores found on the void wall surface. Compared with the hierarchically porous polyHIPE fabricated with decane as porogen (in-situ swelling, conventional route), the ex-situ swelling strategy endowed the materials semblable complex pore morphology but much less damage to its compression performance. The young's modulus of the hierarchically porous polyHIPE herein was 37% higher than that obtained by a conventional way. Afterwards, the hierarchically porous polyHIPE was utilized as a carrier for AgNPs (AgNPs@polyHIPE). The AgNPs@polyHIPEs exhibited eminent catalytic activity and recyclability for the reduction of the rhodamine B. Thereby, a facile approach for preparation of high strength and hierarchically porous polyHIPE was presented, and the resulted polyHIPE can be an ideal support for noble metal nanoparticle catalysts.

Controllable synthesis of a self-assembled ultralow Ru, Ni-doped Fe2O3 lily as a bifunctional electrocatalyst for large-current-density alkaline seawater electrolysis

Highly efficient and stable bifunctional electrocatalysts that can be used for large-current-density electrolysis of alkaline seawater are highly desirable for carbon-neutral economies, but their facile and controllable synthesis remains a challenge. Here, self-assembled ultralow Ru, Ni-doped Fe 2 O 3 with a lily shaped morphology was synthesized on iron foam (RuNi-Fe 2 O 3 /IF) via a facile one-step hydrothermal process, in which the intact lily shaped RuNi-Fe 2 O 3 /IF was obtained by adjusting the ratio of Ru/Ni. Benefitting from the Ru/Ni chemical substitution, the as-synthesized RuNi-Fe 2 O 3 /IF can act as free-standing dual-function electrodes that are applied to electrocatalysis for the hydrogen evolution (HER) and oxygen evolution reactions (OER) in 1.0 mol L −1 KOH, requiring an overpotential of 75.0 mV to drive 100 mA cm −2 for HER and 329.0 mV for OER. Moreover, the overall water splitting catalyzed by RuNi-Fe 2 O 3 /IF only demands ultralow cell voltages of 1.66 and 1.73 V to drive 100 mA cm −2 in 1.0 mol L −1 KOH and 1.0 mol L −1 KOH seawater electrolytes, respectively. The electrodes show remarkable long-term durability, maintaining current densities exceeding 100 mA cm −2 for more than 100 h and thus outperforming the two-electrode system composed of noble catalysts. This work provides an efficient, economical method to synthesize self-standing bifunctional electrodes for large-current-density alkaline seawater electrolysis, which is of significant importance for ecological protection and energy exploitation. A self-assembled ultralow Ru, Ni-doped Fe 2 O 3 (RuNi-Fe 2 O 3 /IF) catalyst with a lily-shaped morphology grown on iron foam was synthesized using a controllable hydrothermal method. Benefitting from the Ru/Ni chemical substitution, RuNi-Fe 2 O 3 /IF possesses benchmark electrocatalytic activity and stability toward HER and OER in 1.0 mol L −1 KOH and 1.0 mol L −1 KOH seawater electrolytes.

Carbothermal Shock Synthesis of High Entropy Oxide Catalysts: Dynamic Structural and Chemical Reconstruction Boosting the Catalytic Activity and Stability toward Oxygen Evolution Reaction

AbstractMixed transition‐metals (TM) based catalysts have shown huge promise for water splitting. Conventional synthesis of nanomaterials is strongly constrained by room‐temperature equilibria and Ostwald ripening. Ultra‐fast temperature cycling enables the synthesis of metastable metallic phases of high entropy alloy nanoparticles, which later transform to oxide/hydroxide nanoparticles upon use in aqueous electrolytes. Herein, an in situ synthesis of non‐noble metal high entropy oxide (HEO) catalysts on carbon fibers by rapid Joule heating and quenching is reported. Different compositions of ternary to senary (FeNiCoCrMnV) HEO nanoparticles show higher activity towards catalyzing the oxygen evolution reaction (OER) compared to a noble metal IrO2 catalyst. The synthesized HEO also show two orders of magnitude higher stability than IrO2, due to stronger carbide‐mediated intimacy with the substrate, activated through the OER process. Alloying elements Cr, Mn and V affect OER activity by promoting different oxidation states of the catalytically active TM (Fe, Ni and Co). Dissolution of less stable elements (Mn, V and Cr) leads to enhancements of OER activity. Dynamic structural and chemical perturbations of HEO oxide nanoparticles activate under OER conditions, leading to enlargement in ECSA by forming mixed single atom catalysts and ultra‐fine oxyhydroxide nanoparticles HEOs.

Enhanced solar light-driven hydrogen evolution of activated carbon sphere supported TiO2 hybrid nanocomposites

Solar-driven photocatalytic water splitting has a great promising impact and versatile green approach to producing hydrogen gas from solar energy for future energy storage devices. Furthermore, noble metal free catalysts have significant benefits in photon induced charge carrier transfer and faradic reaction for photocatalytic water splitting. Herein, we successfully synthesized the garlic peel-derived activated carbon sphere (ACS) and nanocomposite with TiO2 nanoparticles (NPs) using a facile hydrothermal technique for photocatalytic water splitting. The surface morphology, optical property and photocatalytic water splitting activity of prepared hybrid nanocomposite are thoroughly investigated with respect to the different ratios of ACS. In photocatalyst water splitting analysis, the optimal hybrid catalyst of ACS (6 % wt) with TiO2 NPs shows enhanced photocatalytic performance with the hydrogen production rate of 203 μmol g−1 h−1 under solar irradiation. The excellent solar driven water splitting performance of optimal hybrid catalyst has been owing to the enhanced photon harvesting ability and formation of the favorable pathway to effective charge separation and migration on TiO2/ACS surface. Thus, the proposed biomass supported nanocomposite scheme as a hybrid photocatalyst represents to develop the effective bio-mass assisted photocatalyst for solar water splitting process.

Carboxylate-assisted ZIF-derived Co nanoclusters anchoring hierarchically porous carbon as high-efficient zinc-air batteries cathode catalysts

Metal and nitrogen-doped carbon (M-N-C) catalysts are generally considered to be ideal substitutes for platinum-based noble metal oxygen reduction catalysts. Owing to the significant Fenton effect of the Fe element and the subsequent instability, the Fenton-free Co-based N–C catalyst should perform better in ORR. Pyrolysis of metal-organic frameworks (MOFs) is commonly used to make Co-based N–C catalysts. Still, most of the MOF-derived catalysts reported so far have a microporous structure, which results in hindered mass transfer and partial Co-Nx active sites that cannot function as catalysis. Herein, Co nanoclusters (NCs) with high loading (7.96 wt%) were prepared on hierarchically porous carbon substrates via a carboxylate-assisted strategy. The mesoporous structure of Co nanoclusters/nitrogen-doped hierarchically porous carbon (Co NCs/HPNC) can facilitate mass transport. The smaller size Co nanoclusters can increase the contact area between the carbon matrix and Co-Nx active sites to effectively expose more active centers and increase the density of Co-Nx active sites. A synergistic effect of the two can greatly improve ORR results. Surprisingly, the Co NCs/HPNC catalyst shows excellent ORR activity under alkaline conditions, and Co NCs/HPNC has a better half-wave potential (0.88 V vs. 0.84 V) compared with 20 wt% Pt/C. And it only loses 5% of its current density after 36,000 s of operation, which is significantly less than Pt/C (20%). Furthermore, Co NCs/HPNC battery have a greater open-circuit potential, power density, and specific capacity than Pt/C-based zinc-air batteries (1.51 V, 109.6 mW cm−2, 818.1 mAh gZn−1 vs. 1.46 V, 92.4 mW cm−2, 716.8 mAh gZn−1). This discovery paves the way for high-efficiency electrocatalysts with hierarchically porous architectures and a large number of metal loads to be developed.

Unravelling the Influence of Oxygen on the Degradation Mechanisms of Fe-N-C Oxygen Reduction Reaction Catalysts

Pyrolyzed iron-nitrogen-carbon materials (Fe-N-C) comprising mostly atomic Fe-Nx moieties are the most mature class of noble metal free catalysts for the oxygen reduction reaction (ORR) in acidic media. Such catalysts show excellent performance in proton exchange membrane fuel cell (PEMFC), approaching that of platinum-based catalysts. [1] However, an important performance loss is observed during operation, in conditions mimicking those of a PEMFC. [2] To shed fundamental light onto the degradation mechanisms at stake, two different Fe-N-C materials were prepared, one using a metal organic framework (MOF) and the other a sacrificial support method (SSM), and are labelled Fe-N-C_MOF and Fe-N-C_SSM, respectively. These materials were characterized before and after two different accelerated stress tests (ASTs: 10 k cycles, 0.6-1.0 V vs. RHE, 3s-3s, 0.1 M H2SO4, 80°C) under Ar or O2 atmosphere. Stronger degradation and higher ORR mass activity loss were observed when the AST is performed in O2 vs. Ar-saturated acidic electrolyte. For AST under Ar condition, physicochemical characterisations revealed a demetallation process and the eventual occurrence of a clustering mechanism whereas for AST performed in O2 atmosphere, a decrease of the Fe content and the formation of Fe oxide particles was observed (Figure 1).Keywords: Electrocatalysis, Fe-N-C, Oxygen Reduction Reaction, Durability, PEMFC Acknowledgements These studies were financed by the French National Research Agency in the frame of the CAT2CAT (grant number n°ANR-16-CE05-0007) and the ANIMA (grant number n°ANR-19-CE05-0039) projects.

Sacrificial Template-Assisted Mechanochemical Production of Highly Active Bifunctional Fe-N-C Catalysts

Bifunctional catalyst materials development for energy storage and conversion technologies is notoriously demanding in terms of electrochemistry (low stability, sluggish kinetics and high total overpotential (∆E)) and logistics (environmental safety, production methodologies and cost).Noble metal electrocatalysts are proven to be good bifunctional catalysts and as a result are being used as benchmark catalysts. However, the environmental and economic sustainability is severely compromised due to the scarcity of these metals. The alternative option is based on first-row transition metal heteroatom-doped carbon materials. Low cost, high availability, great electrocatalytic activity and stability promise to be a suitable noble metal free catalyst for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR).This work showcases a high performance Fe-N-C type material with sustainable synthesis and efficient activity towards ORR and OER. Unlike various classical methods for electrocatalyst synthesis, the developed methodology combines mechanochemistry and application of sacrificial template, which yields materials with superior bifunctional oxygen electrocatalytic performance.