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Trillion of cigarette butts are annually littered without being recycled. This work aims at valorizing the whole cigarette butts and their components (paper, filter and tobacco) into Fe‐Nx‐C electrocatalysts for oxygen reduction reaction (ORR) in acid and alkaline media. The pristine wastes were pyrolyzed at 450 °C, activated with KOH at 700 °C, blended with iron phthalocyanine (FePc) precursor, and heat‐treated at 600 °C to produce a robust Fe‐Nx‐C material with ORR active units. The effect of the cigarette components on the final electrocatalytic activity was evaluated by thoroughly investigating the surface chemistry with XPS. The electrocatalysts displayed similar results among the different components in both media due to comparable surface chemistry, especially concerning the nitrogen functional groups. The highest performance was obtained in alkaline where the electrocatalysts from whole cigarettes and paper (CIGF_450 and CIGPF_450) showed an E1/2 of 0.89 V vs RHE, slightly larger than that of Pt/C with 40 wt % of Pt, which encouraged to replace Pt‐based electrocatalysts in alkaline fuel cells. [ABSTRACT FROM AUTHOR]

It is a great challenge to synthesize efficient electrocatalysts for overall water splitting, especially non‐noble metal catalysts. Herein, one‐dimensional polycrystalline nanoneedles composed of CoO−Co9S8 nano heterostructures, in situ grown on carbon fiber paper are prepared for efficient overall water electrolysis. Due to strong electronic coupling, charge densities of Co2+/Co3+ in Co9S8 and Co2+ in CoO are favorably modified at the interface of CoO and Co9S8, resulting in optimized reaction intermediates absorption and greatly enhanced bifunctional HER/OER activities. CoO−Co9S8/CFP delivers a current density of 10 mA cm−2 in alkaline electrolyte at overpotentials of 184 mV and 270 mV for HER and OER, respectively. When used as electrocatalyst for overall water splitting, it needs a low cell potential of 1.66 V to realize water electrolysis at 10 mA cm−2. This work provides a new strategy to tune the electronic structures of transitional metal active sites via constructing nano heterostructures for efficient water electrolysis. [ABSTRACT FROM AUTHOR]

Metal organic framework (MOF)‐based materials have been widely studied and reported as efficient electrocatalysts for the hydrogen evolution reaction (HER), owing to their high surface areas, controllable structures, and tunable pore sizes. However, the intrinsically poor electrical conductivity of most MOFs hinders their directly applications as electrocatalysts. Herein, copper‐centered MOFs (HKUST‐1) have been electrodeposited directly onto the current collector. These electrochemically prepared HKUST‐1@carbon paper hybrids exhibited significantly enhanced electrocatalytic performances for the HER, including a positively shifted of onset potential, a lower overpotential, and a smaller Tafel slope, as compared to the conventional hydrothermally prepared HKUST‐1. The proposed electrodeposited synthesis strategy for MOF‐based electrocatalysts is fast, efficient, mild, and environmentally friendly. This work may also extend to other MOF materials and any conductive substrate, thus providing a facile strategy for the preparation of MOF‐based catalysts with high efficiency and low cost. [ABSTRACT FROM AUTHOR]

The stability of Fe−N−C oxygen reduction reaction (ORR) electrocatalysts has been considered a primary challenge for their practical application in proton exchange membrane fuel cells (PEMFCs). While several studies have attempted to reveal the possible degradation mechanism of Fe−N−C ORR catalysts, there are few research results reporting on their stability as well as the possible Fe species formed under different voltages in real PEMFC operation. In this work, we employ in‐situ X‐ray absorption near‐edge structure (XANES) to monitor the active‐site degradation byproducts of an atomically dispersed Fe−N−C ORR catalyst under a H2/O2‐operating PEMFC at 90 % relative humidity and 80 °C. For this, stability tests were carried out at two constant cell voltages, namely 0.4 and at 0.8 V. Even though the ORR activity of the Fe−N−C catalyst decreased significantly and was almost identical at the end of the tests for the two voltages employed, the analysis of the XANES recorded under H2/N2 configuration at 0.6 and 0.9 V within the stability test suggests that two different degradation mechanisms occur. They are demetalation of iron cations followed by their precipitation into Fe oxides upon operation at 0.8 V, versus a chemical carbon oxidation close to the active sites, likely triggered by reactive oxygen species (ROS) originated from the H2O2 formation, during the operation at 0.4 V. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDs) have garnered attention as potential catalysts for water splitting owing to their unique structures, diverse electronic properties, and composition from earth‐abundant elements. While certain TMD catalysts, notably MoS2, have shown promising activity for hydrogen evolution reactions (HER), achieving performance comparable to traditional platinum catalysts remains a challenge. While significant effort has been invested into understanding the effect of TMD's structural properties, such as defectiveness and crystalline phases, recent work has emphasized the role of extrinsic factors on HER. This review summarizes the current understanding of the impact of commonly overlooked electrocatalytic effects that exhibit an enhanced importance in TMD‐based HER. By combining recent advances in theoretical modeling and experimental work, we review the dominating effects of extrinsic factors including electronic resistance, interfacial barriers, surface roughness, oxidation, and valence impurities. Our work aims to provide insights into optimizing TMDs as highly efficient catalysts for HER, facilitating future advancements in hydrogen generation technology. [ABSTRACT FROM AUTHOR]

The integration of different catalytic modalities to control precursors, intermediates, and products requires a method for understanding these complex systems. A modular analytical platform is presented here that allows for catalytic conversion reactions and the delivery of catalytically transformed analytes to subsequent surface enhanced Raman scattering (SERS) detection zones. The paper‐based platforms are compatible for studying biochemical conversion reactions and electrochemical transformations. The full oxidation of glycerol to carbon dioxide follows a cascade reaction of 9 steps, chosen to illustrate the use of a molecular, biological, and metallic catalyst. Designated catalytic reaction zones and SERS detection zones integrated into the pores of paper at specific locations allows all of the reactions to take place within the pores of the analytical platform. Multiple chemical reactions were performed in sequence and the SERS spectra of the resulting intermediates and products were measured. [ABSTRACT FROM AUTHOR]

The efficiency of water splitting for clean production of hydrogen energy is largely limited by the sluggish kinetics of the oxygen evolution reaction (OER). Thus, it is of great significance but still remains challenging to develop stable, efficient, and economical catalysts that could provide a high current density at a low overpotential. In this work, we report an economical synthesis of metal organic framework (MOF) derived Ni‐doped CoS2, grown on carbon fiber paper (Ni‐doped CoS2/CFP), as a new OER catalyst with high catalytic activity and durability. The binder‐free Ni‐doped CoS2/CFP electrode exhibits a very low overpotential of 270 mV (versus RHE) at 10 mA cm−2, a Tafel slope of 79 mV dec−1, and high durability during 3000 cyclic voltammetry sweeps. Such a remarkable OER performance exceeds that of most of noble‐metal‐free materials and even commercial IrO2. The significantly improved OER performance is largely ascribed to the synergic effects of Ni doping and the conductive CFP catalyst support, leading to an enhanced electron and mass transfer during the OER process. We believe that the as‐prepared Ni‐doped CoS2/CFP material holds great promise as an economical OER electrocatalyst for energy‐related applications. Metal‐organic framework derived Ni‐doped CoS2 nanoparticles grown on carbon fiber paper act as efficient, stable, and economical electrocatalysts for the oxygen evolution reaction, showing an overpotential as low as 270 mV at 10 mA/cm2 with a Tafel slope of 79 mV/dec. [ABSTRACT FROM AUTHOR]

Electrocatalytic hydrogen evolution reaction (HER) is a promising strategy to solve and mitigate the coming energy shortage and global environmental pollution. Searching for efficient electrocatalysts for HER remains challenging through traditional trial‐and‐error methods from numerous potential material candidates. Theoretical high throughput calculation assisted by machine learning is a possible method to screen excellent HER electrocatalysts effectively. This will pave the way for high‐efficiency and low‐price electrocatalyst findings. In this review, we comprehensively introduce the machine learning workflow and standard models for hydrogen reduction reactions. This mainly illustrates how machine learning is used in catalyst filtration and descriptor exploration. Subsequently, several applications, including surface electrocatalysts, two‐dimensional (2D) electrocatalysts, and single/dual atom electrocatalysts using machine learning in electrocatalytic HER, are highlighted and introduced. Finally, the corresponding challenge and perspective for machine learning in electrocatalytic hydrogen reduction reactions are concluded. We hope this critical review can provide a comprehensive understanding of machine learning for HER catalyst design and guide the future theoretical and experimental investigation of HER catalyst findings. [ABSTRACT FROM AUTHOR]

Molybdenum oxide MoO3 has been widely used in catalysts and electrochemical energy devices, but, to date, has not been investigated as an electrocatalyst in redox flow cells. In this study, MoO3 in the form of micro-flakes was introduced onto carbon paper as an electrocatalyst and MoO42− as electrolyte additive for the vanadium redox couple reactions in the vanadium redox flow battery (VRFB). When the carbon paper was modified with MoO3 or MoO42− added to the electrolyte, the peak potential separations were measured as 171 and 203 mV for V2+/V3+ and 130 and 111 mV VO2+/VO2+ redox reactions, respectively, as compared with 306 and 144 mV for the bare pre-treated carbon paper. A vanadium redox flow cell with MoO3-CP electrodes exhibited a voltage efficiency of 85.4 % at 100 mA cm−2. The power density reached 200 mW cm−2 at a current density of 150 mA cm−2 when cycled within the voltage range of 0.6-1.7 V. These results indicate that MoO3-based modification is a promising method for high power density VRFB applications. [ABSTRACT FROM AUTHOR]

Hydrogen has garnered considerable attention as an environmentally friendly due to its sustainability and exceptional energy density, surpassing other chemical fuels. For H2 production, electrochemical water splitting is an economically viable and eco‐friendly method. Developing well‐organized electrocatalysts for electrochemical water splitting is pivotal in enabling long‐term hydrogen production, the critical component in the transition toward a cleaner and more environmentally sustainable energy landscape. During the last decades, to aid in oxygen evolution and hydrogen evolution reactions, numerous tungsten carbide‐based electrocatalysts have been established. WC developed as a promising candidate for electrolytic hydrogen generation. This review first explores the historical background and fundamental mechanisms underlying water splitting and subsequently investigates the field of WC‐based electrocatalysts. Furthermore, in both HER and OER, the thorough analysis examines the electrocatalytic performance of electrocatalysts based on WC. Finally, it discusses the challenges and prospects of developing WC‐based electrocatalysts for OER and HER, shedding light on their potential contributions to the sustainable energy landscape. [ABSTRACT FROM AUTHOR]

In this work, catalytic performance of MoS2 supported on Mo2TiC2 and Ti3C2 MXenes towards the oxygen reduction reaction (ORR) was studied. These materials were synthesised through an etching route of MAX phases as precursors of MXenes, followed by a hydrothermal treatment to coat them with MoS2. This procedure generated MoS2 nanospheres covering the MXenes, which were verified by SEM‐EDX mapping, Raman spectroscopy and XPS. Activity of these materials towards ORR was studied by RRDE, comparing its performance with that of individual MoS2 and MXenes. As main features, it was demonstrated that production of HOO− occurring on the composites decreases in comparison with individual materials. Long‐term stability tests performed in O2‐saturated electrolyte showed a drop in the activity of the materials due to the increase in the production of HOO−, although no morphological or compositional changes were observed. Despite this result, the improvement of the catalytic properties of the individual materials means that these composites can be considered as candidates to be used as supports of active non‐noble metal nanoparticles in the cathodes of anion exchange membrane fuel cells (AEMFCs). [ABSTRACT FROM AUTHOR]

Sustainable energy development can no longer be met by fossil fuels alone. Hence, electrochemical water splitting containing oxygen and hydrogen evolution reactions is appealing as a clean energy pathway. As respects the water splitting efficiency which is largely determined by the selectivity, durability, and intrinsic activity of the electrocatalysts, one of the most challenging questions when studying these materials is "which category of electrocatalysts will show the best performance in this issue?" The best electrocatalysts for water splitting still come from noble metals. Although these materials show particularly good efficiency, but due to the scarce resources their massive use is limited. Therefore, the noble metal‐free materials due to their stability, efficiency, abundance and variety of reaction sites were introduced as an interesting candidate for electrochemical water splitting reactions. In this review, based on the important above‐mentioned points, our attention was focused on key categories based on transition metals (TMs), metal organic framework derived (MOF‐derived), carbon‐based hybrids, graphitic carbon nitride (g‐C3N4) hybrids, and bio‐assisted electrocatalysts. These compounds have shown significant activity and stability for broad electrocatalysis applications in water splitting reactions and displaying remarkable potential to replace with noble metal‐based catalysts. This comprehensive review identifies rational strategies for designing and synthesizing high‐performance novel noble metal‐free electrocatalysts for water splitting. [ABSTRACT FROM AUTHOR]

The growing demand for sustainable energy sources has spurred significant studies to optimize the potency of fuel cell technology. Direct urea fuel cell (DUFC) has gained attention due to their energy density, eco‐friendliness, and potential applications in power generation using urea from various sources, including wastewater and urine. Efficient electrocatalysts are pivotal in DUFCs, and nickel‐based catalysts, particularly in the form of NiOOH, have demonstrated cost effectiveness, excellent stability in alkaline media, and good activity for urea oxidation reaction. However, low‐density and durability are still the major limitation in the overall DUFC performance. This review provides a comprehensive analysis of the latest development in Ni‐based catalysts, covering synthesis methods, factors influencing the catalytic activity as well as their implications for DUFC performance durability and commercial viability. In addition, another important factor including the use of different oxidant and electrolyte medium is also elaborated. Based on this review, 2D‐3D Ni‐based materials with the addition of other metals and the use of non‐oxide nickel binary compound are predicted to be the future evolution of the effective nickel‐based catalysts. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting is a highly effective method for carbon‐free hydrogen production. While significant efforts have been made to develop efficient and cost‐effective electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), the optimization of electrode surface properties has been largely overlooked. Inadequate mass diffusion, especially at high bath voltage, hampers the energy transfer efficiency of water electrolysis. To overcome these challenges, precise design of superaerophobic/superhydrophilic electrodes can effectively separate gas bubbles from the catalyst surface and enhance mass transfer, improving overpotential and Faraday efficiency. This article underscores the importance of designing electrocatalysts with well‐designed surface properties to address these challenges. It also discusses characterization techniques for evaluating surface properties and provides examples of applications for superaerophobic/superhydrophilic electrodes in energy storage and conversion systems, electrochemical biosensors, and industrial processes, etc. Overall, optimizing the surface properties of electrocatalysts holds promise for enhancing the efficiency of gas‐involving reactions and energy conversion systems. [ABSTRACT FROM AUTHOR]

Due to their low cost, accessibility of resources, and improved stability and durability, carbon‐based nanomaterials have attracted significant attention as cathode materials for oxygen reduction reactions. These materials also exhibit intrinsic physical and electrochemical features. However, their potential for use in fuel cells is constrained by low ORR activity and slow kinetics. Carbon nanomaterials can be functionalized and doped with heteroatoms to change their morphologies and generate a large number of oxygen reduction active sites to lessen the problems. Doping the carbon lattice with heteroatoms like N, S, and P and functionalizing the carbon structure with −OCH3, −F, −COO−, −O− are two of these modifications that can change specific properties of the carbon nanomaterials like expanding interlayer distance, producing a large number of active sites, and enhancing oxygen reduction activity. When compared to pristine carbon‐based nanomaterials, these doped and functionalized carbon nanomaterials, including their composites, exhibit accelerated rate performance, outstanding stability, and higher methanol tolerance. This article summarizes the most recent developments in heteroatom‐doped and functionalized carbon‐based nanomaterials, covering different synthesis approaches, characterization methods, electrochemical performance, and oxygen reduction reaction mechanisms. As cathode materials for fuel cell technologies, the significance of heteroatom co‐doping and transition metal heteroatom co‐doping is also underlined. [ABSTRACT FROM AUTHOR]

Highly efficient electrocatalysts play important roles in electrochemical water splitting for hydrogen production, including the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Metal‐organic frameworks (MOFs) are porous crystalline materials, exhibiting strong potential as precursors for obtaining outstanding electrocatalysts. MOF‐based electrocatalysts, including MOFs and MOF‐derived electrocatalysts, have become an increasingly important part of catalysts in the field of electrochemical water splitting, but their catalytic performance, especially their activity and stability, still have a lot of room for improvement. In this paper, the preparation strategy of MOF‐based electrocatalysts and improvement methods of catalytic properties were reviewed, including morphology‐controlled methods and composition‐controlled methods. We also focused on the structure–property relationships, which determine the electrocatalytic activity for water splitting reactions. Finally, the challenges and development prospects were discussed for the MOF‐based electrocatalysts, which might provide some insight for future applications in electrochemical water splitting. [ABSTRACT FROM AUTHOR]

The shift towards cheaper, non‐platinum group metal electrocatalyst materials for clean energy technologies is coupled with challenges in maintaining long‐term performance. For practical purposes, electrocatalytic stability typically focuses on catalyst electrochemical performance over time. However, a deeper understanding of catalyst material property changes during operation is needed to enable material‐specific design strategies for long‐term stabilization. In the last several decades, improvements in material characterization techniques have made it possible to probe the composition, structure, and degradation products of catalysts in situ/operando. Herein we review the current understanding of in situ/operando material stability of Co‐based electrocatalysts for the oxygen evolution (OER) and reduction reactions (ORR) in acidic and alkaline environments. We focus on in situ/operando materials characterization of three categories of Co‐based OER/ORR catalysts: oxides and (oxy)hydroxides, mixed‐metal catalysts, and non‐oxide materials. This review aims to compile and compare the results from multiple studies and techniques to provide insight into the role that the starting material, pH, and applied potential have on the active surface and stability of Co‐based materials. We conclude by highlighting directions that have been underexplored with opportunities for continued research including improving in situ/operando characterization, methods to probe long‐term material changes, and the development of operando studies on full‐scale devices. Using Co‐based materials as a case study, this review shows the vital role that in situ/operando characterization must play in the future of improving electrocatalyst stability. [ABSTRACT FROM AUTHOR]

The Cover Feature illustrates the use of electrochemical paper‐based analytical devices (ePADs); the image focuses on the possible coupling of the electrode with smartphones to perform in situ analysis in different fields. This Review focuses on several aspects that are required to prepare an efficient ePAD, such as paper choice and characterization, device construction, applications, and the difficulties that still need to be surpassed. More information can be found in the Review by W. J. Paschoalino et al. on page 10 in Issue 1, 2019 (DOI: 10.1002/celc.201800677). [ABSTRACT FROM AUTHOR]

In fuel cells, the generally low oxygen reduction reactions (ORR) rate at the cathode is a major factor limiting the overall performance of fuel cell, so the development of high‐performance, stable and inexpensive ORR electrocatalysts is a major researching direction. Nano‐electrocatalysts, especially one‐dimensional (1D) electrocatalysts, exhibit good catalytic behavior in fuel cell reactions due to their unique anisotropic structure, large specific surface area, high elasticity and excellent stability. To date, many advanced 1D electrocatalysts have been reported for optimizing the cathode ORR of fuel cells. Therefore, a comprehensive review of the structural design of 1D nano‐electrocatalysts and a systematic analysis of their enhanced performance still need further summarized and concluded. In this review, we firstly introduce the main synthetic methods of 1D electrocatalysts, and then discuss the recent advances and advantages of different structured 1D electrocatalysts involving nanofibers, nanotubes, nanorods, nanochains, nanowires, nanobelts, nanoneedles, nanowhiskers, and coaxial nanocables. In addition, we also introduce 1D electrocatalysts while highlighting advanced strategies and preparation methods for these different structured 1D electrocatalysts to improve ORR performance. Finally, we prospect the future development of 1D ORR electrocatalysts. [ABSTRACT FROM AUTHOR]

In this paper, Bi2O3 electrocatalysts for the electroreduction of CO2 to formate were synthesized with different morphologies, including nanoparticles and thin nanorods. Comparatively, Bi2O3 nanoparticles have higher catalytic activity than Bi2O3 thin nanorods. The Faradaic efficiency of formate formation at a moderate potential of −1.2 vs. RHE in aqueous solution could reach 91 %. In addition, a maximum current density for formate production of up to 22 mA cm−2 was achieved, which is almost 3 times higher than that of Bi2O3 thin nanorods. In particular, the catalytic activity of the Bi2O3 nanoparticle catalyst was almost stable over a 23‐hour period of electrolysis, exhibiting its application prospect in the electroreduction of CO2 to formate. Upcycling: nanoparticles and thin nanorods of Bi2O3 as catalysts for the electroreduction of CO2 to formate are synthesized. The Bi2O3 nanoparticles show higher catalytic activity than the thin nanorods. A Faradaic efficiency of 91 % at a moderate potential of −1.2 vs. RHE is found in aqueous solution. A maximum current density of up to 22 mA cm−2 is achieved, with a stable activity over a 23‐hour period of electrolysis. [ABSTRACT FROM AUTHOR]

Mg‐air batteries are regarded as one of the most promising electrochemical energy storage and conversion devices. Developing high‐performance, low‐cost and durable non‐noble metal electrocatalysts for oxygen reduction reaction (ORR) at cathode is extremely critical for promoting the practical applications of Mg‐air batteries. The bimetallic M−N−C catalysts possess the superior ORR activity and stability due to the synergetic effect of metal atoms. Herein, prussian blue analogues (PBA) were employed as precursors to prepare bimetallic M−N−C electrocatalysts. The CuCo@N/C and Co@N/C were derived from CuCo−PBA and CoCo−PBA calcined under different temperatures. The bimetallic CuCo@N/C nanoparticles pyrolyzed at 800 °C (CuCo@N/C‐800) displays superior ORR performances and outstanding stability in alkaline and neutral electrolytes. The primary Mg‐air batteries assembled with the CuCo@N/C‐800 as the cathode catalyst displays better discharge performances than that of Co@N/C‐800. This work provides an effective strategy to synthesize bimetallic and non‐noble ORR catalysts for Mg‐air batteries. [ABSTRACT FROM AUTHOR]

Transition metal (TM)‐based catalysts are widely studied for their unique advantages in water splitting. Despite significant progress, efficient kinetic regulation strategies for TM‐based materials in electrocatalysis and real‐time monitoring of the dynamic evolution of reaction processes are still in the initial stages. Introducing heterogeneous components into the TM‐based catalyst and forming a specific interface are beneficial to adjust the catalyst interface environment and chemical adsorption behavior, thereby accelerating the kinetic process. In this review, the kinetic improvement strategies of TM‐based electrocatalysts are timely and comprehensively summarized, including interface engineering, defect engineering, doping engineering and crystal face engineering. The main in‐situ/in‐operando characterization methods, including Raman spectroscopy, X‐ray photoelectron spectroscopy, synchrotron X‐ray absorption spectroscopy and infrared spectroscopy, are further summarized. Finally, we outline the current challenges and identify the opportunities facing this emerging area. [ABSTRACT FROM AUTHOR]

One of the most important current topics in the renewable and sustainable energy scenario is the CO2 electro‐reduction reaction (CO2RR), which is an alternative and important route for its conversion into various high value‐added chemicals, therefore making up a CO2 recycling process. Despite its importance and the works already developed in this field, many challenges still need to be overcome for CO2RR to reach high values of efficiency and selectivity. This is even more challenging considering that this reaction occurs with the transfer of several electrons, making the investigation and elucidation of the reaction mechanism a real need. Thus, several characterization techniques have been employed, and specially, the on‐line Electrochemical Mass Spectrometry (EC‐MS) technique emerges as a powerful tool, thus making possible to improve the understanding of reaction pathways, through the identification of products and intermediaries, and allowing the screening of electrocatalyst potentials for CO2RR. Herein, we present the evolution of adaptations of general electrochemical cell designs for the study of the CO2RR. [ABSTRACT FROM AUTHOR]

Pyrolysis is a necessary procedure for synthesizing carbon‐based nonprecious metal electrocatalysts via stimulating interaction and carbonization of precursors. In this work, ramping rates that correlated with thermal gradient has been investigated to reveal the configuration evolution of the precursors. Spectra characterizations demonstrated that ramping rates affected decomposition and aromatization of precursors. Increasing ramping rates improved the percentage of doped nitrogen and defects, promoting dispersion of Co atoms in the carbonaceous matrix and increasing density of active sties. In addition, the size variation of NaCl template under different ramping rates modifies the porous structure of Co/N−C electrocatalysts, greatly increasing the percentage of macropores and micropores at rapid ramping rates. As a result, electrocatalysts obtained at 5 °C min−1 exhibit comparable catalytic activity to that of Pt/C due to highly dispersed active sites and rational percentage of porosity, facilitating the sufficient reaction of oxygen along the catalysts. These results shed lights on regulating physical properties of carbonaceous electrocatalysts. [ABSTRACT FROM AUTHOR]

Carbon nanomaterials, such as carbon nanotubes and graphene doped with heteroatoms, have drawn much attention, owing to their activity as a fuel cell electrocatalyst. This discovery is very important, as the wide application of low- and intermediate-temperature fuel cells is partly hindered by the need for precious-metals, such as platinum, as the electrocatalyst. Here, we report multi-walled carbon nanotubes (MWCNTs) as the active electrode component for the oxygen reduction reaction (ORR) in solid acid fuel cells (SAFCs) and their in operando changes of surface chemistry and structure. We show, for the first time with fuel cell measurements, the effective (time-dependent) electrocatalytic behavior of MWCNTs in SAFC cathodes. For all measurements, the MWCNTs were platinum free and were not doped with heteroatoms during or after the synthesis. AC impedance spectroscopy of the electrochemical cells, MWCNT|CsH2PO4|MWCNT, with and without a DC bias, were performed and the long-term stability was evaluated over a 20 day period. Scanning electron microscopy, Raman, and XPS spectroscopy, before and after the electrochemical measurements, show significant changes in the surface chemistry and structure of the MWCNTs. We observe an increase in the surface oxygen concentration and an increased electrochemical activity. However, this active state is transient in nature, as other chemical degradation processes become more dominant. We conclude that carbon nanomaterials are promising as electrochemically active SAFC materials; however, challenges with stability need to be overcome for a realistic application. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen production plays a major role in technologies for renewable energy storage. Water and urea electrolysis (WE, UE) are promising processes in this regard. The oxygen evolution reaction (OER) and urea oxidation reaction (UOR), respectively, are limiting the efficiency of the overall process. As catalysts for these reactions, metal‐organic frameworks (MOF) have gained increasing attention due to their combinations and co‐existence of metal and organic moiety properties. Here, we investigated the catalytic behavior of Ni MOF (1,3,5‐Benzenetricarboxylic acid (BTC)) towards OER and UOR in alkaline medium on carbon paper (CP) as a support. The Ni MOF exhibits 346 mV overpotential (η) at a current density of 10 mA cm−2, 79.03 A g−1 specific‐mass activity at 400 mV of η than compared to wet chemically prepared (WCP) NiO and RuO2 for OER in 1 M KOH. Meanwhile, ≈230 mV of η at 10 mA cm−2 current density with appreciable stability for 12 hours for Ni MOF in 30 % KOH was also observed. For UOR in UE, Ni MOF shows an onset potential of 1.34 V vs. RHE and 63.15 mA cm−2 current density at 1.5 V vs RHE in 1 M KOH in the presence of 1 M urea. The observed results of OER and UOR catalytic behavior are better than wet chemically prepared (WCP) NiO and noble benchmark RuO2 catalyst under identical conditions. The results suggested that the MOF plays a major role in enhancing the catalytic activity by the facile formation of Ni(OH)2/NiOOH, stability and electronic properties due to their porous and interconnected structure. [ABSTRACT FROM AUTHOR]

Abstract: Lithium‐oxygen (Li−O2) batteries show great potential to become one of the most promising energy‐storage and conversion systems owing to their ultrahigh theoretical specific energy (∼3505 Wh kg−1). However, commercialization of Li‐O2 batteries is constrained by a large charging overpotential caused by the sluggish electrode kinetics and low conductivity of the discharge product, resulting in unsatisfied energy efficiency and poor cyclability. In this paper, aiming to address these issues, we propose unique orderly arranged three‐dimensional (3D) flower‐like MoS2 nanospheres combined with carbon nanotubes (f‐MoS2@CNTs) as an efficient cathode catalyst for Li−O2 batteries. Homogeneously dispersed CNTs on the surface of MoS2 can not only increase the electrical conductivity and thereby lowering the charge overpotential, but also maintain the structural integrity of the cathode, improving the cyclic reversibility. Benefiting from the unique 3D flower‐like structure with an interconnected porous network and the excellent catalytic activity of MoS2, the Li−O2 battery with a f‐MoS2@CNTs catalyst achieved a lower charge overpotential (1.02 V) and exhibited excellent cyclic reversibility with 141 cycles until the terminal voltage decreased below 2 V at a current density of 500 mA g−1. The reasonable design of the f‐MoS2@CNTs‐based cathode thus provides a promising solution for practical applications of Li−O2 batteries. [ABSTRACT FROM AUTHOR]

Abstract: Composites of graphitic carbon layers and transition metals or metal alloys have received considerable attention for use as non‐precious‐metal catalysts for ecofriendly energy devices. In this paper, we report graphitic carbon‐supported NiCo alloys (NiCo@GC) that function as non‐precious‐metal electrocatalysts for the oxygen reduction reaction under alkaline conditions. In particular, we examined the effect of the pyrolysis temperature on the oxygen reduction activity. The catalyst prepared at 600 °C provided an oxygen reduction half‐wave potential (E1/2) of 0.81 V – only 10 mV less than that of a commercial Pt/C catalyst (0.82 V) – with the transfer of almost four electrons. Structural and chemical studies indicated that the excellent activity and stability of the NiCo@GC catalysts resulted from the strong interactions between (and the combined effects of) the metal and the carbon, dictated by the annealing temperature. [ABSTRACT FROM AUTHOR]

Electrochemical CO2 reduction (ECO2RR) is a promising way to convert CO2 into valuable products, while requiring highly active and selective electrocatalysts. Herein, we synthesize a series of AgIn/In2O3 catalysts with AgIn bimetallic core and In2O3 shell structure for ECO2RR to produce formate. The AgIn bimetallic core improved the conductivity of the catalysts and the In2O3 shell was reduced to In that served as active sites during the electrochemical reduction process. The activity and selectivity of formate production is related to the indium content in the AgIn/In2O3 catalyst. The optimized Ag50In50@In2O3 catalyst exhibited a high faradaic efficiency of 83 % at −0.9 V and −1.0 V vs. RHE for formate and the corresponding H2 selectivity was largely suppressed to below 10 % of the applied potentials. There was no significant decay in current density and faraday efficiency of formate after 12 hours of stability testing. Density functional theory calculations indicated that the adsorption energy of *OCHO intermediate on the In shell was reduced due to the Ag−In interface interaction and enhanced charge transfer compared with pure In surface, which lead to the increased selectivity of formate. [ABSTRACT FROM AUTHOR]

Discovery of new catalysts is crucial for future growth and development of environmentally friendly energy conversion processes e. g. the production of hydrogen by water electrolysis. We developed an aerosol‐based synthesis technique as a comparatively fast and facile method to prepare multi‐metal catalysts. 22 different quinary metal compositions were synthesized and investigated with respect to their activity for the oxygen evolution (OER) and the glycerol oxidation (GOR) reactions. The impact of the element composition and the homogeneous distribution of the elements in the particles on catalytic performance were evaluated. The highest activity for OER was found for Co20Cu20Ni20Fe20Zn20. For GOR, Ag‐containing catalysts were the most active, however, in most cases Ag was locally enriched and not homogeneously mixed with the other metals in the particles. Ag‐based catalysts outperformed similar compositions containing one or more noble metals. The GOR selectivity of selected catalysts during long‐term electrolysis was also investigated and it was shown that varying the catalyst composition via aerosol‐based synthesis is a potential way to modulate the GOR selectivity. [ABSTRACT FROM AUTHOR]

The physical and chemical properties of inorganic materials significantly depend on their crystal structures. Therefore, precise design of structures can promote the development of highly active electrocatalysts. Due to the present environmental issues, it is desirable to establish a structural factor that regulates the anodic oxygen evolution reaction (OER) in water splitting. Herein, we demonstrate structural descriptors using nine kinds of unreported iron‐based multimetal oxides with complicated structures and 15 kinds of previously reported iron‐based oxides. Density functional theory simulations find that their OER activities cannot be explained by the electronic descriptor, i. e. charge‐transfer energy. In contrast, the OER activities exhibit clear correlations with structural descriptors. To objectively determine the most dominant structural descriptor for OER electrocatalysis on iron‐based oxides, data‐driven machine learning (ML) is exploited. Thus, ML analysis reveals that Fe−O bond length is the most dominant structural descriptor for electrocatalytic OER on iron‐based oxides. [ABSTRACT FROM AUTHOR]

Taking cognizance of the United Nations Sustainable Development Goal 7 "affordable and clean energy", metal–organic frameworks (MOFs) and derived materials have spurred research interest in electrocatalysis. New findings have made headway in water splitting (oxygen evolution reaction and hydrogen evolution reaction) and other electrocatalysis, including the oxygen reduction reaction and electrochemical CO2 reduction. Thanks to their structural versatility and compositional modularity, MOFs offer bespoke design paradigms for electrocatalyst development. Albeit most advances in this area are predicated upon direct carbonization (pyrolysis) of MOFs/MOF composites, eschewing these energy‐intensive and high‐cost methods, this review summarizes all recent advances in MOF‐based electrocatalysts exclusively prepared through indirect post‐treatments. [ABSTRACT FROM AUTHOR]

Mitigating high energy costs related to sustainable H2 production via water electrolysis is important to make this process commercially viable. Possible approaches are the investigation of low‐cost, highly active oxygen evolution reaction (OER) catalysts and the exploration of alternative anode reactions, such as the electrocatalytic isopropanol oxidation reaction (iPOR) or the glycerol oxidation reaction (GOR), offering the possibility of simultaneously lowering the anodic overpotential and generating value‐added products. A suitable class of catalysts are non‐noble metal‐based perovskites with the general formula ABO3, featuring rare‐earth metal cations at the A‐ and transition metals at the B‐site. We synthesised a series of LaFe1‐xCoxO3 materials with x=0–0.70 by automated co‐precipitation at constant pH and subsequent calcination at 800 °C. X‐ray diffraction studies revealed that the phase purity was preserved in samples with x≤0.3. The activity towards the OER, iPOR, and GOR was investigated by rotating disk electrode voltammetry, showing a relation between structure and metal composition with the activity trends observed for the three reactions. Additionally, GOR product analysis via high‐performance liquid chromatography (HPLC) was conducted after 24 and 48 h electrolysis in a circular flow‐through cell setup, pointing out a trade‐off between activity and selectivity. [ABSTRACT FROM AUTHOR]

After a century of research on electrocatalytic reactions, a universal theory of electrocatalysis is still not established due to limited understanding of complex energy conversion processes at electrified electrode‐electrolyte interfaces. Most of the research efforts directed toward the acceleration of important electrocatalytic reactions (e. g. hydrogen evolution reaction) were in the direction of minimizing activation energy by tuning the adsorption energies of key intermediates. This kind of approach is well‐established and, importantly, in some cases it was valuable by predicting the design of electrocatalysts with advanced properties. However, in some very important research endeavors, advancement in performance of newly designed electrocatalysts could not be attributed to altered/minimized activation energy. Important to note is that modern electrocatalysis almost completely disregards influence of the preexponential factor on reaction rate. In this work, we open some important questions relevant for future of electrocatalysis and electrochemical energy conversion, with special focus on preexponential factor as major contributor to electrocatalytic reaction rate. [ABSTRACT FROM AUTHOR]

Ammonia is an important chemical and a potential carbon‐free hydrogen‐storage material. Currently, the industrial synthesis of ammonia is mainly achieved via the Haber‐Bosch method, which requires high energy, temperatures, and pressures. An alternative method involves the electrocatalytic nitrogen reduction reaction (NRR), which uses an aqueous solution as a medium and requires mild reaction conditions. The key to the NRR is to select an appropriate catalyst to increase the ammonia yield and Faradic efficiency. With their diverse structures and easy regulation, carbon‐based materials can provide abundant active sites for nitrogen absorption and excitation. Moreover, they are abundant, low cost, and readily available, making them promising for use in NRR applications. Accordingly, we review the latest progress in using carbon‐based materials in the NRR, and the future development prospects of NRR catalysts are discussed. Finally, challenges and perspectives of the future research of NRR catalysts are provided. [ABSTRACT FROM AUTHOR]

Exploring highly efficient, durable and low‐cost catalysts for hydrogen evolution reaction (HER) is crucial to promoting the development of electrochemical water splitting systems but remains challenging. In this work, the Ru‐modified CoP nanoflakes on carbon clothes (Ru‐CoP/CC) are fabricated via an in‐situ hydrothermal method, followed by low‐temperature phosphatized treatments. According to X‐ray photoelectron spectroscopy (XPS) measurements, the Ru doping induces the electron deviation from Ru to Co−P, and makes Co ions be an electron‐rich state. It is revealed that the introduction of Ru can effectually reconstruct the electron coordination environment of Co−P. The resultant Ru‐CoP/CC catalyst shows outstanding HER performance with an ultralow overpotential of 45 mV at 10 mA cm−2. Moreover, the obtained catalyst exhibits long‐term durability at 20 mA cm−2 for 20 h in the alkaline solution. This work opens a new avenue to lower the usage of noble metal in electrocatalyst and helps to developing a high‐performance electrocatalyst for HER. [ABSTRACT FROM AUTHOR]

The N‐dedoping‐based defect engineering strategy has been designed as an efficient method to develop advanced defective carbon electrocatalysts for the oxygen reduction reaction (ORR). However, the defective structures, especially the defect density of carbon materials fabricated by this method, were significantly suppressed by the limited N doping level. Herein, an in situ activation/N‐dedoping strategy was proposed to fabricate a controllable defective carbon sponge (DCS) for ORR electrocatalysts, during which a Schiff‐base polymer with a high N content was employed as the carbon precursor and N source while zinc oxide (ZnO) nanoparticles were the thermally removable structure template and activator. As a result, the optimized DCS1100 with a high specific surface area of 1198 m2/g and a low nitrogen content of 2.81 at.% delivered a comparable activity and four‐electron selectivity but superior stability to commercial 30 % Pt/C in 0.1 M KOH electrolyte. [ABSTRACT FROM AUTHOR]

Electrocatalytic water splitting involving the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a crucial and effective pathway to obtain clean and renewable energy resources. The advanced electrocatalysts can significantly reduce the reaction energy barrier to realize high‐efficiency energy conversion. In this regard, noble‐metal catalysts display excellent catalytic performance for the water splitting reaction, but the high cost hinders its large‐scale application. As a low‐cost candidate for noble‐metal catalysts, tungsten oxide is endowed with the variable crystalline phase and adjustable composition, which provide more opportunities to achieve satisfactory catalytic activity by engineering crystal structure and modulating surface electronic states. To promote the reaction activity and stability, some effective strategies have been developed to optimize the surface crystal and electronic structure of tungsten oxide electrocatalysts for overall water splitting. In this review, we especially highlight the latest advances and progress in the exploration of tungsten oxide electrocatalysts for HER and OER, and systematically classify these strategies into several design principles involving adjustable surface morphology, engineering defects, and synergistic catalysis, providing a deep understanding of the relationship between the catalytic activity and crystal structure in the tungsten oxide. Some perspectives are also proposed to guide a rational design of tungsten oxide electrocatalyst for water splitting. [ABSTRACT FROM AUTHOR]

Developing powerful and tolerant catalysts toward hydrogen evolution reaction (HER) is fairly meaningful and critical for the conversion and utilization of green energy. In this work, we exploit an improved, reliable, and convenient strong electrostatic adsorption strategy to synthesize Ru‐based electrocatalysts containing ultra‐small Ru nanoparticles (NPs). As verified by experimental studies and characterization analysis, the optimized treatment can strengthen the powerful interaction for anchoring ultra‐small Ru NPs dispersed on carbon substrate and prevent the migration and agglomeration of Ru NPs during catalytic reactions. It is demonstrated that the designed Ru−KB−H−6H exhibits exceptional HER performance with low overpotential (η10) and Tafel slope (52 mV and 41.5 mV dec−1 in 0.5 M H2SO4, 53 mV and 61.0 mV dec−1 in 1.0 M KOH). As expected, Ru−KB−H−6H displays dramatical stability with no unacceptable decline of LSV performance after 8000 cycles and long‐term test. This finding paves a practical way to fabricate high‐efficient, and steady electrocatalysts toward HER for industrial applications. [ABSTRACT FROM AUTHOR]

Industrial synthesis of ammonia (NH3) involves high energy consumption resulting in intense pollution. Alternatively, electrochemical nitrogen reduction reaction (NRR) to NH3 can be carried out under mild conditions, which is a new green NH3 synthesis method. Herein, cerium zirconium solid solutions (ZrxCe1‐xO2) with different proportions were synthesized by NH3 precipitation method and employed as electrocatalysts for NRR. The performance of the different catalysts in 0.1 mol L−1 Na2SO4 was evaluated with H2O and N2 as reactants. The results show that Zr0.9Ce0.1O2 has the highest Faraday efficiency (FE) of 62.68 % at −1.3 V (vs. Ag/AgCl) and the highest yield rate of NH3 −9.34×10−11 mol cm−2 s−1 at −1.35 V (vs. Ag/AgCl). The impressive FE is due to more oxygen vacancies in Zr0.9Ce0.1O2 introduced by Ce3+, which is more prone to the adsorption of N2 on the catalyst surface and facilitates the electrochemical reaction. [ABSTRACT FROM AUTHOR]

With continuously increasing energy requirements, electrochemical water splitting is a solution to generate hydrogen as a carbon‐free fuel for future energy demands. Water splitting reaction is made up of two half electrochemical reactions ‐ hydrogen evolution (HER) and oxygen evolution (OER). The principal components of these electrochemical reactions are electrode materials, which are currently facing challenges in performance improvement, thus developing advanced electrode materials or electrocatalysts is essential. Metal‐organic frameworks (MOFs) are crystalline porous materials that have recently exhibited great potential as precursor for designing excellent water splitting electrocatalysts. These MOF‐derived materials are not attractive just because of high‐performance in electrocatalysis but also owing to their fascinating nanostructures, which are difficult to achieve by other synthetic methods. Search for well‐shaped nanostructured materials using MOF as a precursor for water splitting have attracted the attention in recent time and is a rapidly growing research area. This review summarizes the progress towards MOF‐derived electrocatalysts for water electrolysis especially focusing on nanostructure engineering, structure‐property correlations, and their bifunctional HER/OER performances. Performance of these bifunctional catalysts in two‐electrode electrolyzers are also discussed. Finally, existing obstacles and the future prospects of MOF‐derived bifunctional water splitting electrocatalysts are elaborated. [ABSTRACT FROM AUTHOR]

Redox flow batteries (RFBs), which are based on the redox reaction of vanadium ions, are expected to be a promising energy buffer for renewable energy because of their large‐scale potential. However, the reaction overvoltage associated with the redox of vanadium ions is large, and highly active electrocatalysts are urgently needed. In this study, we prepared thin‐film model electrodes to evaluate the catalytic activities of tungsten oxide, which is known to be an electrocatalyst for accelerating the redox of vanadium ions and investigated the reaction mechanism. The results showed that tungsten oxide only catalyzed the reduction of VO2+, while carbon only catalyzed the oxidation of VO2+, but not both redox reactions. Our results revealed for the first time that the catalytic sites active in the charging and discharging of RFB are different, which is an important finding for the construction of highly active electrocatalysts. [ABSTRACT FROM AUTHOR]

Designing bifunctional electrocatalytic sites with outstanding activity and durability in one component toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is quite essential for rechargeable Zn‐air batteries. Herein, a novel core‐shell composition of Co9S8/Co embedded multi‐channel carbon nanofiber was successfully developed as efficient electrocatalysts for ORR and OER by step pyrolysis. The precursor of polystyrene was degraded while polyacrylonitrile was cross‐linked to hexatomic ring during the pro‐oxidation process, therefore, endowing the longitudinal and parallel channels along the fibers' skeleton in the subsequent carbothermal reduction steps, which affords the superhighway for competent mass transmission and outstanding electrochemical specific area. On the other hand, the potent synergistic effect from precision‐designed core–shell species of Co9S8/Co allows the composite multi‐channel carbon fiber excellent ORR/OER bifunctional catalytic activities, with a gap of 0.89 V between the half‐wave potential toward ORR and potential of OER at a current density of 10 mA/cm2. Additionally, the rechargeable Zn‐air batteries were capable of operating steadily over 500 discharging/charging cycles at a constant current density of 5 mA/cm2. [ABSTRACT FROM AUTHOR]

Heteroatoms doped carbon‐based metal‐free catalysts are important candidates as alternatives for precious group metal (PGM) catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) – two of the most important reactions in electrochemical energy conversion and storage areas. Despite the significant efforts in developing heteroatoms doped metal‐free electrocatalysts with enhanced electrocatalytic activity, few studies focus on their bifunctional activities for ORR and OER due to the unclear catalytic mechanism and complicated active sites configurations. Herein, a series of nitrogen and phosphate co‐doped carbon‐based catalysts (NP/C) are successfully synthesized via a precursor modulation strategy. In this method, 5‐aminouracil, 2, 6‐diaminopyridine and 1, 3‐diaminobenzene are selected to modulate pyridinic N (NP), graphitic N (NG) and pyrrolic N (NPY) sites, respectively, while phytic acid is used as P sites. The results demonstrate that the N and P co‐doped graphene with NP+NG+P configuration shows increased ORR performance, and on the other hand, the NP+NPY+P configuration enhances OER. Density functional theory (DFT) calculation demonstrates that different NP configurations formed by precursor modulation induce different electronic structure on surrounding carbon atoms, providing a possibility to manipulate intermediates energy in reaction pathway for ORR and OER. This study sheds new light on revealing the intrinsic correlation between active site configurations and catalytic bifunctional activity and selectivity of graphene based electrocatalysts for oxygen redox reactions. [ABSTRACT FROM AUTHOR]

This paper describes the preparation and electrocatalytic activity of nanocomposites composed of reduced graphene oxide and Au25 clusters. Well-defined nanocomposites are prepared by coating the surface of reduced graphene oxide with multiple layers of Au25 film, the thickness of which can be precisely controlled according to the preparation conditions. The electrocatalytic activity of the nanocomposites are examined for the reduction of [Ru(NH3)6]3+ and in the oxygen reduction reaction by chronoamperometry and electrochemical impedance spectroscopy as a function of Au25 thickness. Whereas the catalytic rate constants obtained for the reduction of [Ru(NH3)6]3+ are found to be rather constant with varying Au25 thickness, those for the oxygen reduction reaction increased drastically with an increasing number of Au25 layers. This increase can be ascribed to the porous structures generated in the nanocomposites. The porous channels generated in the nanocomposites offer confined space surrounded by electrified surface, greatly enhancing the electrocatalytic activity for the oxygen reduction reaction. Additional rotating disk electrode and rotating ring-disk electrode voltammetry show that the nanocomposites support an efficient four-electron reduction of oxygen. [ABSTRACT FROM AUTHOR]

Abstract: Carbon and transition metals have emerged as promising candidates for many energy storage and conversion devices. They facilitate charge transfer reactions whilst showing a good stability. These materials, fabricated as freestanding electrodes pose the potential of simplified electrode manufacturing procedures whilst demonstrating excellent electrocatalytic, mechanical, and structural properties, resulting from interconnected (via chemical or van der Waals force bonded) network structures. In such freestanding configuration, the lack of a binder leads to a better conductivity, ease in the manufacturing processing, and allows a lower catalyst mass loading, all of which lead to obvious benefits. This Minireview summarizes different fabrication techniques of freestanding non‐precious‐metal oxygen electrocatalysts along with their performance towards the oxygen evolution reaction (OER) and/or oxygen reduction reaction (ORR). Here, we discuss electrocatalysts produced by using freestanding substrates and those obtained through the self‐assembly of different precursors. The advantages of using freestanding versus non‐freestanding configurations are also pondered. Challenges and perspectives for freestanding electrocatalysts are presented at the end of the Minireview as a guideline for future studies in the field. This work is expected to serve as inspiration for science colleagues to develop further studies into design, processing and testing strategies of freestanding low‐cost oxygen electrocatalysts. [ABSTRACT FROM AUTHOR]

Water electrolysis over a wide pH range offers promising technology for hydrogen production, which requires highly stable and active electrocatalysts for the hydrogen evolution reaction (HER). Herein, polyallylamine (PA)-functionalized ultrafine rhodium nanoparticles (Rhô€€€ uNPs) uniformly anchored on three-dimensional graphene aerogel (GA) nanocomposites (PA@Rhô€€€ uNPs/GA) are synthesized by using a facile surface adsorption-chemical reduction method at room temperature. Physical characterization shows that the PA@Rhô€€€ uNPs/GA nanocomposites have three-dimensionally porous architecture and that PA@Rhô€€€ uNPs with a 1.3 nm size are uniformly dispersed on the GA surface. Electrochemical measurements show that the molecular weight of PA affects the HER activity of PA@Rh- uNP nanocomposites. The molecular weight-optimized PA@Rh- uNPs/GA nanocomposites with 10% Rh mass show higher HER activity than the commercial 20% Pt/C electrocatalyst over a wide pH range, which originates from proton or water enrichment at the electrode/solution interface due to the specific function of - NH2 groups at PA molecules. [ABSTRACT FROM AUTHOR]

Understanding the structure-property relations of non-precious metal heteroatom co-doped carbon electrocatalysts exhibiting high activity as well as long-term durability for both ORR and OER remains challenging but is indispensable for the development of bifunctional ORR/OER electrocatalysts. We propose BN-co-doped graphitic 2D carbon nanostructures impregnated with controlled amount of transition metals (M-BCN; M=Co, Ni, Fe, Cu) as bifunctional ORR/OER electrocatalysts. Co-BCN outperformed the Ni-, Fe-, Cu-based BCN catalysts exhibiting potential values of 0.87 V and 1.62 V at 1 mA/cm² and 10 mA/cm² during ORR and OER, respectively. Importantly, Co-BCN shows bifunctional cyclic stability (??; EOER EORR=0.75 V) of up to 300 cycles in 1 M KOH for a duration of 20 h with total activity loss of only 10.2% (ORR) and 6.2% (OER), respectively. A low loading of the metal precursors was used to preserve porosity and to facilitate the formation of metal nanoparticles or M-NxB/C type species embedded in the graphitic carbon layers. The B-N-co-doped graphitic layers also protect the embedded metal nanoparticles explaining the observed longterm stability. [ABSTRACT FROM AUTHOR]

High‐performance electrocatalysts have been deeply investigated and widely explored to improve the energy conversion efficiency in advanced electrochemical technologies. As a vital rare‐earth oxide, CeO2 has shown great promise in catalysis for its feasible redox feature, high oxygen storage capacity, abundant surface oxygen defects, and structural robustness. The structural characteristics will boost the electrocatalytic activity and durability of CeO2‐based hybrids. In this Review, relevant research results focusing on recent hybrid materials between CeO2 and other functional species, including metal, metal oxides/hydroxides, metal sulfides and phosphides, towards the oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and nitrogen reduction reaction (NRR) are summarized. This Review also highlights the key role of CeO2 and the structural design strategies in the hybrid electrocatalysts, including ion doping, interface and defect engineering, electronic structure optimization, and morphology control for catalytic output enhancement. Lastly, some scientific challenges and perspectives have been proposed, aiming to promote the development of other CeO2‐based hybrids for energy related electrocatalysis. [ABSTRACT FROM AUTHOR]

Nitrogen‐doped porous carbon (NPC) materials have attracted increased attention for zinc‐air battery (ZAB) applications because of their comparable electrocatalytic activity to precious metals. However, few metal‐free NPC catalysts exhibit an oxygen reduction reaction performance better than Pt catalysts, together with high oxygen evolution reaction catalytic activity. Herein, an efficient oxygen electrocatalyst based on highly integrated carbon nanofiber (CNF) and NPC aerogels, with CNF as the core and NPC as the shell, is demonstrated. The NPC@CNF aerogels are prepared through a large‐scale, direct pyrolysis of metal‐organic frameworks and bacterial cellulose hybrids. This mono‐doped carbon material with nitrogen heteroatoms displays outstanding bifunctional performance compared to the individual counterparts, which demonstrates the effectiveness of morphological and structural engineering. Density functional theory calculations reveal that the active sites with the participation of multi‐electrons weaken the O−O bond and facilitate the four‐electron oxygen reduction in the dissociation pathway. The ZAB based on the NPC@CNF air electrode exhibits a peak density of 96 mW cm−2 and a stable charge–discharge durability of over 420 cycles with an overpotential increase of only 0.10 V, indicating that the mono‐doped NPC@CNF performs as one of the best bifunctional catalysts among those recently reported metal‐based and metal‐free catalysts. [ABSTRACT FROM AUTHOR]