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Carbon dioxide electroreduction reaction (CO2RR) can take full advantage of sustainable power to reduce the continuously increasing carbon emissions. Recycling CO2 to produce formic acid or formate is a technologically and economically viable route to accomplish CO2 cyclic utilization. Developing efficient and cost‐effective electrocatalysts with high selectivity towards formate is prioritized for the industrialized applications of CO2RR electrolysis. From the previous explored CO2RR catalysts, Sn, Bi and In based materials have drawn increasing attentions due to the high selectivity towards formate. However, there are still confronted with several challenges for the practical applications of these materials. Therefore, a rational design of the catalysts for formate is urgently needed for the target of industrialized applications. Herein, we comprehensively summarized the recent development in the advanced electrocatalysts for the CO2RR to formate. Firstly, the reaction mechanism of CO2RR is introduced. Then the preparation and design strategies of the highly active electrocatalysts are presented. Especially the innovative design mechanism in engineering materials for promoting catalytic performance, and the efforts on mechanistic exploration using in situ (ex situ) characterization techniques are reviewed. Subsequently, some perspectives and expectations are proposed about current challenges and future potentials in CO2RR research. [ABSTRACT FROM AUTHOR]

Water splitting is a critical process for the production of green hydrogen, contributing to the advancement of a circular economy. However, the application of water splitting devices on a large scale is primarily impeded by the sluggish oxygen evolution reaction (OER) at the anode. Thus, developing and designing efficient OER catalysts is a significant target. NiFe‐based catalysts are extensively researched as excellent OER electrocatalysts due to their affordability, abundant reserves, and intrinsic activities. However, they still suffer from long‐term stability challenges. To date, few systematic strategies for improving OER durability have been reported. In this review, various advanced NiFe‐based catalysts are introduced. Moreover, the OER stability challenges of NiFe‐based electrocatalysts in alkaline media, including iron segregation, structural degradation, and peeling from the substrate are summarized. More importantly, strategies to enhance OER stability are highlighted and opportunities are discussed to facilitate future stability studies for alkaline water electrolysis. This review presents a design strategy for NiFe‐based electrocatalysts and anion exchange membrane (AEM) electrolyzers to overcome stability challenges in OER, which also emphasizes the importance of long‐term stability in alkaline media and its significance for achieving large‐scale commercialization. [ABSTRACT FROM AUTHOR]

Atomically precise composite site‐based catalysts with new electrocatalytic synergistic mechanisms and enhanced electrocatalytic activities have emerged as a frontier in the electrocatalysis community. This topical review focuses on the recent research advances of atomically precise metal composite sites‐based electrocatalysts. This work first demonstrates an overview of the configurations of atomically precise composite sites, including a discussion of the advanced methods employed for understanding the composite sites. The review then provides a comprehensive organization of the previously reported methodologies of synthesizing electrocatalysts with atomically precise composite sites. Representative case studies are provided, starting from the simple one‐step pyrolysis strategy to the species‐by‐species multi‐step pyrolysis strategy. Based on the preceding discussions of the catalyst materials, the review further discusses the unique electrocatalysis mechanisms raised by the composite sites, that are different from the routine single species sites. The electrocatalytic systems mainly involve the oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, nitrogen reduction reaction, and carbon dioxide reduction reaction. The themes of this section include the true active center determination for composite sites and various types of electrocatalytic synergy mechanisms. Finally, critical unanswered questions and remaining challenges, as well as promising underexplored research directions are identified. [ABSTRACT FROM AUTHOR]

Facilitating the cleavage of a NN bond and suppressing the competition hydrogen evolution reaction is essential, and but still remains a challenge in nitrogen reduction reaction (NRR). Crystal phase tailoring is an effective approach to optimize the energy barrier during the NRR process to improve the catalytic efficiency. Herein, a boron‐doping strategy to induce phase transfer from hexagonal Mo2C to cubic Mo2C for regulating the electronic structure and catalytic properties of electrocatalysts toward NRR is reported. The B doped cubic Mo2C is found to increase the exposure of active sites, regulate the d band center of Mo for enhancing the adsorption and activation of nitrogen, and reduce the energy barrier of NRR pathway, giving rise to a high ammonia yield of 52.1 μg h−1 mg−1 at −0.6 V versus reversible hydrogen electrode under ambient conditions. More importantly, the hydrogen adsorption on the surface of electrocatalyst is significantly inhibited due to the B‐doping, further improving the faradic efficiency to 36.9%, which is 4 times that of hexagonal Mo2C (9%). This work not only sheds light on the atomic‐scale design of efficient NRR electrocatalysts, but also provides a promising avenue for synchronizing the catalytic activity and selectivity for catalytic reactions. [ABSTRACT FROM AUTHOR]

Highly efficient electrocatalysts play an integral part in developing renewable energy conversion and storage technologies. Despite considerable efforts devoted to synthesizing electrocatalysts with superior performance, the identification of active moieties and understanding of reaction mechanisms under practical conditions still remain elusive. Herein, the substantial progresses in unraveling the local electronic and atomic structure optimizations of nanocatalysts for gas‐involved electrocatalysis, disclosing real active sites, and clarifying their relationships with intrinsic activities by combining advanced characterization techniques with computational simulations are summarized. The continuous development of in situ and ex situ characterization tools, particularly at multi‐scale resolution, to monitor or even directly observe the active center structure is systematically discussed, which is divided into four main categories based on the type of active sites: atomically dispersed active sites, vacancies, heteroatom doping sites, and edge sites. Current challenges and perspectives in both fundamental area and industrial application are finally proposed for the future research direction of next‐generation electrode materials. The aim of this review is to provide mechanistic insights into the real catalytically active structure with the assistance of newly developed characterization techniques, guiding the rational design and structure engineering of advanced functional materials with outstanding activity, selectivity, and durability. [ABSTRACT FROM AUTHOR]

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Abstract: As an emerging battery technology, metal–air flow batteries inherit the advantageous features of the unique structural design of conventional redox flow batteries and the high energy density of metal–air batteries, thus showing great potential as efficient electrochemical systems for large‐scale electrical energy storage. This review summarizes the operating principles and recent progress of metal–air flow batteries from a materials and chemistry perspective, with particular emphasis on the latest advanced materials design and cell configuration engineering, which the authors divide into three categories based on the anode species: vanadium–air, zinc–air, and lithium–air flow batteries. Since some of the capabilities developed for metal–air static batteries can be leveraged for next‐generation flow systems, classical works on conventional metal–air batteries are selected and compared with the metal–air flow systems, highlighting the prominent advantages of the latter in achieving high energy capacity and long cycle performance. At the end, a general perspective on current challenges/opportunities and future research directions to promote the commercial application of the metal–air flow battery technology is provided. The aim is to provide a comprehensive overview and to set up a road map for guiding development from conventional static to advanced flow technologies of metal–air batteries. [ABSTRACT FROM AUTHOR]

Abstract: The platinum (Pt) particle electrocatalysts were fabricated by a surfactant-free, electro-deposition technique in the cyclic voltammetric mode for electro-oxidation of ammonia in aqueous solutions. The hierarchical Pt nanoparticles with various morphologies, including sheet-, flower-, prickly sphere- and cauliflower-like shapes, were obtained by controlling the electrodepositing parameters. The amount of Pt loading was determined by an inductively coupled plasma method, and the electrocatalytic activity of the prepared nano-Pt electrocatalysts for the ammonia oxidation was characterized by cyclic voltammetry. The results showed that there is a remarkable effect of the surface morphology of Pt particles on the electrocatalytic activity. In particular, the hierarchical Pt particles have a much higher electrocatalytic activity for the ammonia oxidation than the smooth, spherical Pt particles. The improved electrocatalytic activity is attributed not only to the large electrochemically active surface area (ECSA) achieved, but also to the high electrocatalytic activity per unit ECSA. Electro-deposition technique provides a promising alternative to fabricate high-performance electrocatalysts for oxidation of ammonia in aqueous solutions. [Copyright &y& Elsevier]

Palladium catalysts have attracted widespread attention as advanced electrocatalysts for the formic acid oxidation (FAO) due to their excellent electrocatalytic activity and relatively high abundance. At present, electrodeposition methods have been widely developed to prepare small-sized and highly-dispersed Pd electrocatalysts. However, the customary use of surfactants would introduce heterogeneous impurities, which requires complicated removal processes. In this work, we reported a two-step electrochemical method that employed square-wave potential treatment (SWPT) to modify electrodeposited Pd particles without the use of capping agents. Under the SWPT with a mixed frequency, Pd particles show significantly reduced size and more dispersed distribution, exhibiting a high mass activity of 1.43 A mg−1 toward FAO, which is 4.6 times higher than the counterpart of commercial Pd/C. The increase in electrocatalytic activity of FAO is attributed to the highly developed surface of palladium particles uniformly distributed over the support surface. [ABSTRACT FROM AUTHOR]

Pt monolayers (PtML) supported on nanoparticles with different compositions (i.e., Ru, Rh, Pd, Ir, and Au) were synthesized by the surface–limited redox replacement of underpotentially deposited Cu monolayers on nanoparticle supports. Nanoparticle supports with different compositions were directly deposited on the conducting substrate by a clean and one-step electrodeposition method with controlled deposition potential and time. The whole synthesis process of the electrode was free of surfactants, binders, capping agents and reductants, and without an additional coating process of electrocatalysts. The results show that the specific activity (SA) of PtML electrocatalysts depended strongly on the composition of the nanoparticle support. For example, the PtML supported on the Au nanoparticle exhibited 8.3 times higher SA than that supported on the Ru and Pd nanoparticles. The change in the SA of the PtML supported on different nanoparticles was related to the substrate–induced strain in the PtML resulting from the lattice mismatch between the PtML and the nanoparticle support. As the strain in the PtML changed from the tensile strain to the compressive strain, the SA of the PtML electrocatalysts decreased remarkably. [ABSTRACT FROM AUTHOR]

Abstract One-dimensional transition metal phosphides with large specific surface areas and efficient conductivity have the great potential in both hydrogen and oxygen evolution reaction (HER and OER) as bifunctional catalysts, which are at the heart of water splitting. Herein, we firstly report the controllable synthesis of Co 2 P nanorods through a substrate- and template-free facile phosphating reaction. Electrochemical test results reveal that the synthesized Co 2 P nanorods exhibit superior bifunctional activity with overpotentials of 87 mV for HER and 310 mV for OER at 10 mA cm−2, respectively, relative to Co 2 P/CoP branched nanostructure, CoP nanoparticles and commercial Co 2 P in alkaline media. In addition, the bifunctional Co 2 P nanorods catalysts enable overall water splitting with a cell voltage of 1.65 V to achieve 10 mA cm−2 and stabilized potentials at different current densities testing over 24 h. Further analysis demonstrate that the remarkably bifunctional activity is contributed to high charge transfer efficiency, large contact area with electrolyte and a large number of exposed active sites provided by the rod-like nanostructure. This work should shed light on an industrialized pathway for the future design of phosphide catalysts to apply to overall water splitting even other emerging energy devices. Graphical abstract Image 1 Highlights • Co 2 P nanorods with the diameter and length of around 200 nm and 10–20 nm. • Firstly prepared via a substrate- and template-free facile phosphating reaction. • With the increase in active area and the minimum in charge transfer resistance. • Displaying superior bifunctional activity and stability for water splitting. • Paving the way to in large scale obtain highly active and durable TMPs. [ABSTRACT FROM AUTHOR]

Nickel phosphide has been shown to be active toward hydrogen evolution reaction (HER). In this paper, we demonstrate the phase and composition controllable synthesis of nickel phosphide-based nanoparticles (Ni P-based NPs) via a low-temperature phosphidation reaction (250 °C) using NaH 2 PO 2 as the phosphorus source and the as-prepared Ni(OH) 2 precursor as the nickel source. Interestingly, by changing the NaOH concentration and nickel source used to fabricate Ni(OH) 2 precursors, we could adjust the phases and compositions of as-synthesized Ni P-based nanocatalysts from Ni 5 P 4 , Ni 2 P to Ni 12 P 5 . The different steric hindrance and the electrostatic repulsion of synthesized β-Ni(OH) 2 precursors result in the formation of three Ni P phases with various Ni:P ratios. Electrochemical characterizations reveal that the Ni P-based NPs with P-rich phase (Ni 5 P 4 +Ni 2 P) exhibit remarkable electrocatalytic HER property, with low overpotential ( η ) of 111 mV to reach a current density of 10 mA cm −2 in a 0.5 M H 2 SO 4 media, which is superior than those of pure Ni 2 P ( η = 118 mV) and the Ni-rich Ni P-based counterpart (Ni 12 P 5 +Ni 2 P) ( η = 131 mV). This is attributed to the stronger ensemble effect of P and more active sites provided by P-rich Ni P-based NPs. Our results demonstrate that by tailoring the surface properties of Ni(OH) 2 precursors, the phases and compositions of Ni P-based nanoparticles could be easily tuned, which provides a simple, economic, and green strategy to optimize the HER performance of transition metal phosphide-based electrocatalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • The iodine-doped cobalt-N-C structure on carbon-encapsulated Co nanocrystals were synthesized via a chemical vapor deposition process. • Doping iodine induce the formation of highly active and stable C–pyridinic-N–Co centers as the most vital active sites for oxygen reduction reaction. • The catalyst shows a high half-wave potential of 0.85 V and negligible change even after 10,000 cycles. • For ORR process, the doped halogen atoms can promote the O 2 adsorption strength and generate OOH* on C–pyridinic-N–Co sites. Although transition metal and N co-doped carbon (M-N-C) materials are regarded as the promising electrocatalysts for oxygen reduction reaction (ORR), they still suffer from unsatisfactory activity and stability. Herein, a novel strategy for halogen atom inducing the formation of highly active and stable C–pyridinic-N–Co sites is presented. The iodine doped Co-N-C catalysts formed via a chemical vapor deposition process, which shows a high half-wave potential of 0.85 V and remarkable durability. The introduction of iodine not only lowers the d band center of surface Co atoms and also makes the electronic rearrangement of Co-N-C structure. The unique structure promotes O 2 adsorption strength and generate of OOH*, accelerating the ORR process on the surface of catalytically active sites surface. Moreover, as an air electrode in rechargeable Zn-air battery, the catalyst shows a large peak power density of 120 mW cm−2 and high stable cyclability. Even as flexible batteries, the cathode exhibits good stability and flexibility under different bending states. [ABSTRACT FROM AUTHOR]

It has been a great challenge to directly deposit uniform metal particles onto pristine graphene due to its low surface energy and chemical inertness. Without any surfactant or functionalization, we have developed a unique synthesis of high-quality PtRuNi trimetallic nanoparticles supported on pristine graphene via a simple but effective supercritical route. Due to excellent wettability between supercritical carbon dioxide and the carbon surface, ultrafine metal particles are uniformly and firmly anchored on the graphene sheets. While well retaining its intrinsic structure and outstanding electronic conductivity, the pristine graphene with well-dispersed PtRuNi trimetallic nanoparticles shows significantly improved catalytic activity towards methanol oxidation, which is at least ten times higher than those of the commercial Pt/C and homemade Pt/XC-72 catalysts. The resulting trimetallic hybrid also exhibits high stability as compared to Pt and PtRu/pristine graphene composites and the reduced graphene oxide counterparts. In principle, the supercritical method can be applied to other metal nanoparticles in fabrication of high-performance graphene-based nano-catalysts. [ABSTRACT FROM AUTHOR]

A unique synthesis was developedto immobilize Pd nanoparticleson pristine graphene (PG) sheets via a facile supercritical carbondioxide route. Pristine graphene was obtained by sonication-assistedexfoliation of graphite in an organic solvent. Finely dispersed worm-likePd nanoparticles are homogeneously deposited on the hydrophobic graphenesurfaces. The combination of pristine graphene sheets and well-dispersedPd nanoparticles provided large electrochemically active surface areas (ECSA) for bothdirect formic acid fuel cell (DFAFC) and methanol fuel cell (DMFC).The ECSA values are more than twice as large as those of reduced grapheneoxide and carbon nanotube based counterparts or six times those ofconventional XC-72 carbon black. Significant enhancements were alsoobserved in the electrocatalytic activity and stability measurements.The excellent electrochemical property of Pd/PG is attributable tothe well-preserved graphene structure that ensures electrical conductivityand stability of the composite. Its large surface area also allowsfor the deposition of small size and high dispersion of the Pd nanoparticles.This straightforward synthesis offers a new pathway for developinghighly active electrocatalysts based on pristine graphene with fullyoptimized properties. [ABSTRACT FROM AUTHOR]

Developing active, stable and cost-effective bifunctional electrocatalysts is critical for energy storage and conversion application. Constructing heterogeneous structures can integrate distinct individual properties into one entity and can yield exceptional functionalities. Herein, we report heterogeneous NiS 2 /CoS 2 nanohybrids that are synthesized by successive ion injection method. Benefiting from the synergistic effect, the weak lattice distortion and the electronic modulation, the NiS 2 /CoS 2 electrode exhibits much more catalytic active sites and faster electronic transfer rate, thus leading to better oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) performances in KOH solution than the individual NiS 2 and CoS 2. Moreover, the solid state Zn-air battery (SSZAB) with NiS 2 /CoS 2 as the air electrode exhibits a peak power density of 101 mW cm−2 and a specific capacity of 734 mAh g−1. For practical application, the two-series-connected NiS 2 /CoS 2 -based SSZABs can power light-emitting diode (LED) screens and water splitting system efficiently. In addition, the electrocatalytic properties of NiS 2 /CoS 2 in solid state electrolyte deserve further investigation. This work opens a new way for developing high efficient bifunctional electrocatalysts in KOH solution for electronic device utilization. Image 1 • NiS 2 /CoS 2 nanohybrids were synthesized using successive ion injection method. • The interface structure and lattice distortion increased the catalytic active sites. • NiS 2 /CoS 2 displays efficient bifunctional catalytic properties in KOH solution. • NiS 2 /CoS 2 -based solid state Zn-air battery exhibits excellent power density. [ABSTRACT FROM AUTHOR]