Porous Electrocatalyst Research Articles

Bilayer Porous Electrocatalysts for Stable and Selective Electrochemical Reduction of CO2 to Formate in the Presence of Flue Gas Containing NO and SO2.

The development of stable and selective electrocatalysts for converting CO2 to value-added chemicals or fuels has gained much interest in terms of their potential to mitigate anthropogenic carbon emissions. Most of the electrocatalysts are tested under pure CO2; however, industrial outlet flue gas contains numerous impurities, such as NO and SO2, which poison the electrocatalysts and alter the product selectivity. Developing electrocatalysts that are resistant to such impurities is essential for commercial implementation. Herein, we prepared bilayer porous electrocatalysts, namely, Sn, Bi, and In, on porous Cu foam mesh (Sn/Cu-f, Bi/Cu-f, and In/Cu-f) by a two-step electrodeposition process and employed these electrodes for the electrochemical reduction of CO2 to formate. It was observed that the bilayer porous electrocatalysts exhibited high CO2 reduction activity compared to catalysts coated on a Cu mesh. Among bilayer porous electrocatalysts, Sn/Cu-f and Bi/Cu-f electrocatalysts showed more than 80% faradaic efficiency (FE) toward formate production, with a formate partial current density of around -16 and -10.4 mA cm-2, respectively, at -1.02 V vs RHE. In/Cu-f electrocatalyst showed nearly 40% formate FE with formate partial current density of -15 mA cm-2 at -1.22 V vs RHE. We investigated the effect of NO and SO2 impurities (500 ppm of NO, 800 ppm of SO2, and 500 ppm of NO + 800 ppm of SO2) on these electrocatalysts' selectivity and stability toward formate. It was observed that the Bi/Cu-f electrocatalyst showed 50 h stability with 80 ± 5% formate FE, and Sn/Cu-f showed 18 h stability with above 80 ± 5% efficiency in the presence of NO and SO2 mixed with CO2. Furthermore, we studied the effect of CO2 concentration with Sn/Cu-f and Bi/Cu-f catalysts in the range of 15-100% CO2, for which formate FEs of 45-80% were observed.

Hierarchically Ordered Pore Engineering of Metal-Organic Framework-Based Materials for Electrocatalysis.

Ordered pore engineering that embeds uniform pores with periodic alignment in electrocatalysts opens up a new avenue for achieving further performance promotion. Hierarchically ordered porous metal-organic frameworks (HOP-MOFs) possessing multilevel pores with ordered distribution are the promising precursors for the exploration of ordered porous electrocatalysts, while the scalable acquisition of HOP-MOFs with editable components and adjustable pore size regimes is critical. This review presents recent progress on hierarchically ordered pore engineering of MOF-based materials for enhanced electrocatalysis. The synthetic strategies of HOP-MOFs with different pore size regimes, including the self-assembly guided by reticular chemistry, surfactant, nanoemulsion, and nanocasting, are first introduced. Then the applications of HOP-MOFs as the precursors for exploring hierarchically ordered porous electrocatalysts are summarized, selecting representatives to highlight the boosted performance. Especially, the intensification of molecule and ion transport integrated with optimized electron transfer and site exposure over the hierarchically ordered porous derivatives are emphasized to clarify the directional transfer and integration effect endowed by ordered pore engineering. Finally, the remaining scientific challenges and an outlook of this field are proposed. It is hoped that this review will guide the hierarchically ordered pore engineering of nanocatalysts for boosting the catalytic performance and promoting the practical applications.

Amorphous Engineering of Scalable Metal-Organic Framework-Derived Electrocatalyst for Highly Efficient Oxygen Evolution Reaction.

The engineering of amorphous metal-organic frameworks (MOFs) offers potential opportunities for the construction of electrocatalysts for efficient oxygen evolution reaction (OER). Herein, highly efficient OER performance and durability in alkaline electrolyte are discovered for MOF-derived amorphous and porous electrocatalysts, which are synthesized in a brief procedure and can be facilely produced in scalable quantities. The structural inheritance of MOF amorphous catalysts is significant for the retention of catalytic sites and the diffusion of electrolytes, and the presence of Fe sites can change the electronic structure and effectively control the adsorption behavior of important intermediates, accelerating reaction kinetics. The obtained amorphous A-FeNi can be transformed from FeNi-MOF effortlessly and instantly, and it only needs low overpotentials of 152 and 232mV at 10 and 100mA cm-2 with a Tafel slope of 17mV dec-1 in 1m KOH for OER. Moreover, A-FeNi possesses high corrosion resistance and durability, therefore A-FeNi can work continually for at least 400h at 100mA cm-2. This work may pave a new avenue for the design of MOFs-related amorphous electrocatalyst.

Enhanced Oxygen Reduction Activity of Platinum Micropore

AbstractThe high overpotential of oxygen reduction reaction (ORR) prevents the wide commercialization of fuel cells and metal‐air batteries. To accelerate the reaction rate, porous electrocatalysts draw attention to obtain a higher specific surface area. However, the effect of micropores on ORR kinetics has not been understood because of the non‐uniform pore sizes, length, and tortuosity of practical electrocatalysts. In this study, we evaluate ORR activity in a micropore using platinum model electrodes with arrays of cylindrical pores with a uniform pore diameter of 1.8 nm. The model electrodes having pore lengths of 45, 100, and 380 nm are fabricated, and their ORR performances are examined by electrochemical measurements and numerical simulations in 0.1 mol dm−3 KOH aqueous solution. The intrinsic ORR activity of the micropore is successfully obtained with the electrode having a pore length of 45 nm, where oxygen transport resistance in the micropore has little effect on ORR. It is found that the intrinsic ORR activity of the micropore is higher than that of a planar Pt surface. X‐ray photoelectron spectroscopy and CO stripping voltammetry indicate a downshift of the d‐band center, which can be the origin of the high intrinsic ORR activity.

A self-supported porous NiMo electrocatalyst to boost the catalytic activity in the hydrogen evolution reaction.

To develop hydrogen energy production and address the issues of global warming, inexpensive, effective, and long-lasting transition metal-based electrocatalysts for the synthesis of hydrogen are crucial. Herein, a porous electrocatalyst NiMo/Ni/NF was successfully constructed by a two-step electrodeposition process, and was used in the hydrogen evolution reaction (HER) of electrocatalytic water decomposition. NiMo nanoparticles were coated on porous Ni/NF grown on nickel foam (NF), leading to a resilient porous structure with enhanced conductivity for efficient charge transfer, as well as distinctive three-dimensional channels for quick electrolyte diffusion and gas release. Notably, the low overpotential (42 mV) and fast kinetics (Tafel slope of 44 mV dec-1) at a current density of 10 mA cm-2 in 1.0 M KOH solution demonstrate the excellent HER activity of the electrode, which was superior to that of recently reported non-noble metal-based catalysts. Additionally, NiMo/Ni/NF showed extraordinary catalytic durability in stability tests at a current density of 10 mA cm-2 for 70 h. The porous structure catalyst and the electrodeposition-electrocatalysis technique examined in this study offer new approaches for the advancement of the electrocatalysis field because of these benefits.

Engineering Electronic Structure of Nitrogen‐Carbon Sites by sp3‐Hybridized Carbon and Incorporating Chlorine to Boost Oxygen Reduction Activity

AbstractDevelopment of efficient and easy‐to‐prepare low‐cost oxygen reaction electrocatalysts is essential for widespread application of rechargeable Zn‐air batteries (ZABs). Herein, we mixed NaCl and ZIF‐8 by simple physical milling and pyrolysis to obtain a metal‐free porous electrocatalyst doped with Cl (mf‐pClNC). The mf‐pClNC electrocatalyst exhibits a good oxygen reduction reaction (ORR) activity (E1/2=0.91 V vs. RHE) and high stability in alkaline electrolyte, exceeding most of the reported transition metal carbon‐based electrocatalysts and being comparable to commercial Pt/C electrocatalysts. Likewise, the mf‐pClNC electrocatalyst also shows state‐of‐the‐art ORR activity and stability in acidic electrolyte. From experimental and theoretical calculations, the better ORR activity is most likely originated from the fact that the introduced Cl promotes the increase of sp3‐hybridized carbon, while the sp3‐hybridized carbon and Cl together modify the electronic structure of the N‐adjacent carbons, as the active sites, while NaCl molten‐salt etching provides abundant paths for the transport of electrons/protons. Furthermore, the liquid rechargeable ZAB using the mf‐pClNC electrocatalyst as the cathode shows a fulfilling performance with a peak power density of 276.88 mW cm−2. Flexible quasi‐solid‐state rechargeable ZAB constructed with the mf‐pClNC electrocatalyst as the cathode exhibits an exciting performance both at low, high and room temperatures.

Engineering Electronic Structure of Nitrogen-Carbon Sites by sp3 -Hybridized Carbon and Incorporating Chlorine to Boost Oxygen Reduction Activity.

Development of efficient and easy-to-prepare low-cost oxygen reaction electrocatalysts is essential for widespread application of rechargeable Zn-air batteries (ZABs). Herein, we mixed NaCl and ZIF-8 by simple physical milling and pyrolysis to obtain a metal-free porous electrocatalyst doped with Cl (mf-pClNC). The mf-pClNC electrocatalyst exhibits a good oxygen reduction reaction (ORR) activity (E1/2 =0.91 V vs. RHE) and high stability in alkaline electrolyte, exceeding most of the reported transition metal carbon-based electrocatalysts and being comparable to commercial Pt/C electrocatalysts. Likewise, the mf-pClNC electrocatalyst also shows state-of-the-art ORR activity and stability in acidic electrolyte. From experimental and theoretical calculations, the better ORR activity is most likely originated from the fact that the introduced Cl promotes the increase of sp3 -hybridized carbon, while the sp3 -hybridized carbon and Cl together modify the electronic structure of the N-adjacent carbons, as the active sites, while NaCl molten-salt etching provides abundant paths for the transport of electrons/protons. Furthermore, the liquid rechargeable ZAB using the mf-pClNC electrocatalyst as the cathode shows a fulfilling performance with a peak power density of 276.88 mW cm-2 . Flexible quasi-solid-state rechargeable ZAB constructed with the mf-pClNC electrocatalyst as the cathode exhibits an exciting performance both at low, high and room temperatures.

Bimetallic zeolitic imidazole framework-derived sulfur-doped porous carbon as highly efficient catalysts for oxygen reduction reaction in proton exchange membrane fuel cells

The oxygen reduction reaction (ORR) is the most sluggish half-reaction in fuel cells; therefore, Pt-group metal (PGM)-based electrocatalysts have been employed to circumvent this limitation. However, the use of Pt, which is a precious metal, significantly limits the commercialization of proton-exchange membrane fuel cell (PEMFC) systems because of the high cost and low durability of Pt-based materials. Herein, we introduce advanced S-doped Co–N–C (CoNC) porous electrocatalysts (S-CoNPCs) derived from zeolitic imidazole frameworks as substitutes for PGM-based electrocatalysts. To improve the electrocatalytic activity of CoNC, sulfur doping, and acid etching treatment methods, which are innovative procedures, are employed to obtain high catalytic activity and a large surface area. S-CoNPC demonstrates an extremely improved electrochemical performance for ORR in both alkaline and acidic mediums compared with commercial Pt/C, exhibiting Eonset, E1/2, and limiting current density of approximately 0.91 V, 0.85 V, and −6.7 mA cm−2 (at 0.40 V vs. RHE), respectively, which are in the suitable range for commercializing the PEMFCs system. Furthermore, S-CoNPC, which exhibits high selectivity, stability, and methanol tolerance, is a promising, novel, and advanced non-PGM electrocatalyst for diverse applications.

Hierarchical 2D sheets of N and S co-doped Fe-based electrocatalyst for efficient oxygen reduction in advanced Zn-air battery

Currently, the scientific community is keenly interested in the design and production of efficient and durable transition metal electrocatalysts for oxygen reduction reactions (ORR). Therefore, this study reports a simple and reproducible N and S co-doped two-dimensional (2D) hierarchical porous electrocatalyst is reported. NSC the support material first was obtained by pyrolyzing trithiocyanuric acid (TTCA) and loaded on hemin to obtain the final material named Fe/NSC-800. 2D hierarchical porous structures with the large specific surface area were constructed by using TTCA as the template, S source, and additional N source. The addition of hemin not only retained the morphology of the NSC but also provided source of Fe for Fe/NSC-800. The Fe/NSC-800 possessed the limiting current density of 5.85 mA cm–2 and good ORR stability in 0.1 M KOH solution. Based on the excellent ORR performance of Fe/NSC-800, it was assembled into the primary Zn-air battery, which also exhibited satisfactory open circuit voltage (1.55 V) and energy density (880 W h kg–1). This work has contributed to the rational engineering and fabrication of high-performance ORR electrocatalysts for Zn-air battery applications.

3D Hollow Hierarchical Porous Carbon with Fe-N4 -OH Single-Atom Sites for High-Performance Zn-Air Batteries.

The development of innovative and efficient Fe-N-C catalysts is crucial for the widespread application of zinc-air batteries (ZABs), where the inherent oxygen reduction reaction (ORR) activity of Fe single-atom sites needs to be optimized to meet the practical application. Herein, a three-dimensional (3D) hollow hierarchical porous electrocatalyst (ZIF8@FePMPDA-920) rich in asymmetric Fe-N4 -OHmoieties as the single atomic sites is reported. The Fe center is in a penta-coordinated geometry with four N atoms and one O atom to form Fe-N4 -OH configuration. Compared to conventional Fe-N4 configuration, this unique structure can weaken the adsorption of intermediates by reducing the electron density of the Fe center for oxygen binding, which decreases the energy barrier of the rate-determining steps (RDS) to accelerate the ORR and oxygen evolution reaction (OER) processes for ZABs. The rechargeable liquid ZABs (LZABs) equipped with ZIF8@FePMPDA-920 display a high power density of 123.11mWcm-2 and a long cycle life (300h). The relevant flexible all-solid-state ZABs (FASSZABs) also display outstanding foldability and cyclical stability. This work provides a new perspective for the structural design of single-atom catalysts in the energy conversion and storage areas.

Porosity engineering of biochar‐based single‐atom Ni catalysts to promote CO2 electroreduction over a broad potential window

AbstractDeveloping electrocatalysts for CO2 electroreduction with high activity and superior selectivity is extremely important and desirable from both academic and industrial perspectives. However, owing to competition with hydrogen evolution, highly efficient CO2 reduction is mostly achieved with high CO selectivity in a narrow potential range, which is incompatible with a large cell voltage required for industrial‐level CO2 reduction. Herein, we report an effective strategy to regulate CO2 reduction performances of single‐atom Ni electrocatalysts over a broad potential window by engineering their pore structures (micropores, mesopores, or hierarchical pores with both micropores and mesopores). It is revealed that hierarchically pores can significantly promote CO2 reduction efficiency of single‐atom Ni electrocatalysts. The hierarchically porous electrocatalyst achieves a maximum CO Faradaic efficiency (FECO) of 97.4% at −1.2 V (vs. RHE) and shows high FECO of >85% over a broad potential window from −0.7 to −1.7 V, much superior to electrocatalysts with other pore structures. More impressively, turnover frequency of the hierarchically porous electrocatalyst increases rapidly with increasing the applied potential and reaches 50,067 h−1 at −1.7 V. Such CO2 electroreduction promotion could be attributed to a synergistic effect of micropores for enhancing CO2 adsorption and mesopores for facilitating rapid release of product bubbles, which significantly improves CO2 reduction and suppresses hydrogen evolution.

Dynamic Electrodeposition on Bubbles: An Effective Strategy toward Porous Electrocatalysts for Green Hydrogen Cycling.

ConspectusClosed-loop cycling of green hydrogen is a promising alternative to the current hydrocarbon economy for mitigating the energy crisis and environmental pollution. It stores energy from renewable energy sources like solar, wind, and hydropower into the chemical bond of dihydrogen (H2) via (photo)electrochemical water splitting, and then the stored energy can be released on demand through the reverse reactions in H2-O2 fuel cells. The sluggish kinetics of the involved half-reactions like hydrogen evolution reaction (HER), oxygen evolution reaction (OER), hydrogen oxidation reaction (HOR), and oxygen reduction reaction (ORR) limit its realization. Moreover, considering the local gas-liquid-solid triphase microenvironments during H2 generation and utilization, rapid mass transport and gas diffusion are critical as well. Accordingly, developing cost-effective and active electrocatalysts featuring three-dimensional hierarchically porous structures are highly desirable to promote the energy conversion efficiency. Traditionally, the synthetic approaches of porous materials include soft/hard templating, sol-gel, 3D printing, dealloying, and freeze-drying, which often need tedious procedures, high temperature, expensive equipment, and/or harsh physiochemical conditions. In contrast, dynamic electrodeposition on bubbles using the in situ formed bubbles as templates can be conducted at ambient conditions with an electrochemical workstation. Moreover, the whole preparation process can be finished within minutes/hours, and the resulting porous materials can be employed as catalytic electrodes directly, avoiding the use of polymeric binders like Nafion and the consequent issues like limited catalyst loading, reduced conductivity, and inhibited mass transport.In this Account, we summarize our contributions to the dynamic electrodeposition on bubbles toward advanced porous electrocatalysts for green hydrogen cycling. These dynamic electrosynthesis strategies include potentiodynamic electrodeposition that linearly scans the applied potentials, galvanostatic electrodeposition that fixes the applied currents, and electroshock which quickly switches the applied potentials. The resulting porous electrocatalysts range from transition metals to alloys, nitrides, sulfides, phosphides, and their hybrids. We mainly focus on the 3D porosity design of the electrocatalysts by tuning the electrosynthesis parameters to tailor the behaviors of bubble co-generation and thus the reaction interface. Then, their electrocatalytic applications for HER, OER, overall water splitting (OWS), biomass oxidation (to replace OER), and HOR are introduced, with a special emphasis on the porosity-promoted activity. Finally, the remaining challenges and future perspective are also discussed. We hope this Account will encourage more efforts into this attractive research field of dynamic electrodeposition on bubbles for various energy catalytic reactions like carbon dioxide/monoxide reduction, nitrate reduction, methane oxidation, chlorine evolution, and others.

A Porous Perovskite Nanofiber with Reinforced Aerophobicity for High-Performance Anion Exchange Membrane Water Splitting.

Perovskite oxides stand out as emerging oxygen evolution reaction (OER) catalysts on account of their effective electrocatalytic performance and low costs. Nevertheless, perovskite oxides suffer from severe bubble overpotential and inhibited electrochemical performance in large current densities due to their small specific surface areas and structural compactness. Herein, the study highlights the electrospun nickel-substituted La0.5 Sr0.5 FeO3-δ (LSF) porous perovskite nanofibers, that is, La0.5 Sr0.5 Fe1-x Nix O3-δ (denoted as ES-LSFN-x, x=0, 0.1, 0.3, and 0.5), as high-performance OER electrocatalysts. The most effective La0.5 Sr0.5 Fe0.5 Ni0.5 O3-δ (ES-LSFN-0.5) nanofibers suggest a larger specific surface area, higher porosity, and faster mass transfer than the counterpart sample prepared by conventional sol-gel method (SG-LSFN-0.5), showing notably increased geometric and intrinsic activities. The bubble visualization results demonstrate that the enriched and nano-sized porosity of ES-LSFN-0.5 enables reinforced aerophobicity and rapid detachment of oxygen bubbles, thereby reducing the bubble overpotential and enhancing the electrochemical performance. As a result, the ES-LSFN-0.5-based anion exchange membrane water electrolysis delivers a superior stability of 100h while the SG-LSFN-0.5 counterpart degrades rapidly within 20h under a current density of 100mAcm-2 . The results highlight the advantage of porous electrocatalysts in optimizing the performance of large current density water electrolysis devices by reducing the bubble overpotential.

Electrochemical partial reduction of Ni(OH)2 to Ni(OH)2/Ni via coupled oxidation of an interfacing NiAl intermetallic compound for robust hydrogen evolution

Ni-based porous electrocatalysts have been widely used in the hydrogen evolution reaction (HER) in alkaline water electrolysis, and the catalysts are produced by selective leaching of Al from Ni-Al alloys. It is well known that chemical leaching of Ni-Al intermetallic compound (IMC) generates a high surface area in Ni(OH)2. However, the Ni(OH)2 produced by leaching the Ni-Al intermetallic compound retards the hydrogen evolution reaction, which is attributed to its weak hydrogen adsorption energy. In this study, we controlled the chemical state of Ni using plasma vapor deposition (PVD) followed by heat treatment, selective Al leaching, and electrochemical reduction. X-ray diffraction (XRD), scanning microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS) were used to confirm the phase evolution of the electrocatalysts during fabrication. We reveal that the heat-treated Ni-Al alloy with a thick Ni2Al3 surface layer underwent selective Al leaching and produced biphasic interfaces comprising Ni(OH)2 and NiAl IMCs at the edges of the grains in the outermost surface layer. Coupled oxidation of the interfacing NiAl IMCs facilitated the partial reduction of Ni(OH)2 to Ni(OH)2/Ni in the grains during electrochemical reduction, as confirmed by X-ray photoelectron spectroscopy (XPS). An electrocatalyst containing partially reduced Ni(OH)2/Ni exhibited an overpotential of 54 mV at 10 mA/cm2 in a half-cell measurement, and a cell voltage of 1.675 V at 0.4 A/cm2 for single-cell operation. A combined experimental and theoretical study (density functional theory calculations) revealed that the superior HER activity was attributed to the presence of partially reduced metallic Ni with various defects and residual Al, which facilitated water adsorption, dissociation, and finally hydrogen evolution.

Directional assembly of multi-catalytic sites CoCu-MOFs with porous carbon nanofiber templates as efficient catalyst for microbial fuel cells

Designing catalysts with multi catalytic sites is considered as a promising way to solve the sluggish kinetics of the cathodic oxygen reduction reaction (ORR) and improve the performance of electricity generation in microbial fuel cells (MFCs). In this work, a novel hybrid porous electrocatalyst derived from metal-organic frameworks (MOFs) is successfully synthesized, which combines graphene-carbon coated CoCu alloy nanoparticles grown in vertical alignment on carbon nanofibers (CoCu@N-CNFs). Apart from this, CoCu@N-CNFs containing both Co-Nx and Cu-Nx coordination environments enhance oxophilicity, thereby boosting the intrinsic activity of ORR. As expected, CoCu@N-CNFs-1:1 exhibits a superior ORR half-wave potential (−0.545 V vs. Hg/HgCl2) and high limiting current density (10.09 mA cm−2), exceeding that of 20% Pt/C. Furthermore, the MFC equipped with CoCu@N-CNFs-1:1 catalyst achieves maximum power density and coulomb efficiency, which are 102% and 112% higher than Pt/C, respectively. Moreover, CoCu@N-CNFs-1:1 possesses high antibacterial capacity, inhibiting the biofouling on the cathode surface, which further ensures the effective and continuous occurrence of ORR at the triple-phase interface of MFCs.

2,1,3]-Benzothiadiazole-Spaced Co-Porphyrin-Based Covalent Organic Frameworks for O2 Reduction

Designing N-coordinated porous single-atom catalysts (SACs) for the oxygen reduction reaction (ORR) is a promising approach to achieve enhanced energy conversion due to maximized atom utilization and higher activity. Here, we report two Co(II)-porphyrin/ [2,1,3]-benzothiadiazole (BTD)-based covalent organic frameworks (COFs; Co@rhm-PorBTD and Co@sql-PorBTD), which are efficient SAC systems for O2 electrocatalysis (ORR). Experimental results demonstrate that these two COFs outperform the mass activity (at 0.85 V) of commercial Pt/C (20%) by 5.8 times (Co@rhm-PorBTD) and 1.3 times (Co@sql-PorBTD), respectively. The specific activities of Co@rhm-PorBTD and Co@sql-PorBTD were found to be 10 times and 2.5 times larger than that of Pt/C, respectively. These COFs also exhibit larger power density and recycling stability in Zn-air batteries compared with a Pt/C-based air cathode. A theoretical analysis demonstrates that the combination of Co-porphyrin with two different BTD ligands affords two crystalline porous electrocatalysts having different d-band center positions, which leads to reactivity differences toward alkaline ORR. The strategy, design, and electrochemical performance of these two COFs offer a pyrolysis-free bottom-up approach that avoids the creation of random atomic sites, significant metal aggregation, or unpredictable structural features.

Impact of Pore Structure on Electrochemical Reduction of Carbon Dioxide in Iron- and Nitrogen-Doped Carbon Materials: Solid–Liquid Interface Versus Solid–Gas–Liquid Triple-Phase Boundary

The effect of porosity on the interface microenvironment and catalytic performance of carbon dioxide reduction reaction (CO2RR) is still unclear for iron- and nitrogen-doped carbon-based (Fe/N/C) materials, and previous studies mainly focus on aqueous electrode test conditions rather than a practical working environment. Herein, several Fe/N/C-based catalysts with very different pore structures were prepared and compared to understand how the surface area and micropores affect the CO2RR between aqueous electrode test and practical working conditions with a solid–gas–liquid triple-phase boundary. The apparent current density correlates positively to the surface area in both test conditions. The onset current density where hydrogen evolution reaction starts is irrelevant to the micropore fraction in the aqueous electrode test but correlates negatively to the micropore fraction in a practical working condition. The inconsistency is attributed to different reaction interfaces in both cases, resulting in different interface microenvironments in different pore size ranges. This work helps in designing porous electrocatalysts for CO2RR or beyond.

Single-cell-array biomass-templated architecture of hierarchical porous electrocatalysts for Zn-air and Zn-H2O2 batteries.

Hierarchically macro-meso-microporous ZIF-67/nori-derived electrocatalysts were synthesized by using single-cell-array nori and ZIF-67 as macroporous and microporous templates, and KOH as a meso/micropore-forming reagent. The ZIF-67/nori-800-based Zn-H2O2 battery achieved a high maximum power density, of 476 mW cm-2, and a specific energy density of 964 W h kg-1 at 50 mA cm-2.

Self-standing Co decorated Cu2O/CuS-based porous electrocatalyst for effective hydrogen evolution reaction in basic media

The self-standing Co decorated Cu2O/CuS-based porous electrocatalyst was prepared with the help of simple electrodeposition and hydrothermal method. The structural characterizations of fabricated samples were performed with X-Ray diffraction spectroscopy and X-Ray photoelectron spectroscopy, while the morphology of catalysts was studied with the help of Field-Emission Spectroscopy and Transmission Electron Spectroscopy. The electrochemical performance of the hydrogen evolution reaction was checked in a basic electrolyte. The gradual increment in the electrochemical performance of Cu2O was observed when it underwent sulfurization without and with Co precursor respectively. The best electrochemical performance for hydrogen evolution reaction with an overpotential of 150.29 mV to achieve a geometric current density of 10 mA/cm2 was observed for the Cu2O sample sulfurized with Co precursor. The results of different characterizations suggested that the improved electrochemical performance could be attributed to the increased intrinsic activity and surface porosity of the electrocatalyst after sulfurization.

A Numerical Approach to Optimize Catalyst Layer Structure of Polymer Electrolyte Fuel Cells Using Non-Isothermal Three-Dimensional Simulation

The world is struggling with a rapid increase in energy demand and the exacerbating problems of greenhouse gases (GHG) caused by the widespread exploitation of fossil fuels. These issues, however, have brought the attention of academics, investors, and governments throughout the world to hydrogen as a viable alternative during the transition from fossil resources to renewable energies. Hydrogen could be used to generate electricity using an electrochemical energy conversion device called polymer electrolyte membrane fuel cell (PEMFC), which converts the chemical energy stored in bonds of the fuel (hydrogen) directly to electric power. Although PEMFC technology has advanced significantly over the last decade, complete commercialization of this technology will still need more cost-cutting and performance enhancement [1]. From electrochemical and economic standpoints, the porous electrode is the most crucial of PEMFC components. Electrodes are porous media made up of different constituents that serve as the heart of PEMFC, facilitating different coupled transport phenomena such as heat, mass, and electric charge transfer. As a result, an optimized design of this component might significantly elevate performance and efficiency.In recent years, designing architectured electrodes with the goal of improving overall energy conversion efficiency has started [2, 3]. However, full leverage of such state-of-the-art procedures for designing engineered electrodes strongly depends on the employment of novel design tools. Among various advanced design alternatives, the attention of researchers in different disciplines of engineering has recently been drawn to topology optimization methods [4]. While topology optimization was originally applied to structural mechanics, it has since been expanded to more complicated systems with multiple physics, including heat and fluid. However, with only a few exceptions [5, 6], most topology optimization applications to electrochemical devices are limited to enhancing flow fields to boost reaction dispersion and diminish pressure drop. Moreover, previous research studies like [5] mainly used simplified two-dimensional isothermal models, which are far from reality. Therefore, these studies are incapable of providing a comprehensive insight into optimal spatial distribution of catalyst, electrolyte, and voids in a porous electrocatalyst layer.In the present study, a three-dimensional, non-isothermal, multi-phase model is developed to simulate the performance of PEMFC. The presented model is then used to determine the optimal spatial distribution of the porous electrocatalyst layer constituents, including catalyst, electrolyte, and voids. While increasing the catalyst content in the PEMFC electrode could improve cell performance, its excessive use leads to a substantial increment of cost and oxygen transport resistance. This mass transport resistance problem is especially critical at high current density regions with a higher risk of flooding. Hence, in the present study, the optimization process is formulated as a constrained problem so as to obtain maximum output voltage under a constant total catalyst loading. The results show that in an optimal design, the volume fraction of catalyst and electrolyte should be higher in the region under the channel where there is a higher potential for current density production. At the same time, it is desired to increase the porosity in the region under the rib where oxygen delivery involves more resistance. Acknowledgment This work was supported by JSPS KAKENHI Grant Number 21H04540.