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The controllable construction of non-noble metal based bifunctional catalysts with high activities towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of great significance, but remains a challenge. Herein, we reported an effective method to synthesize cobalt-nitrogen doped mesoporous carbon-based bifunctional oxygen electrocatalyst with controllable phosphorus content (Co-N-P X -MC, X = 0.5, 1.0, 1.5, 2.0). The mesoporous carbon substrate endowed the as-prepared samples with more exposed active surface (236.50 m 2 ·g −1 ) and the most appropriate doping ratio of phosphorus had been investigated to be 1.5 (Co-N-P 1.5 -MC). For ORR, Co-N-P 1.5 -MC exhibited excellent catalytic activity with more positive onset potential (1.01 V) and half-wave potential (0.84 V) than the other samples. For OER, Co-N-P 1.5 -MC also showed a low overpotential of 415 mV. Combining experimental results and density-functional theory (DFT) calculations, the outstanding bifunctional catalytic performance of Co-N-P 1.5 -MC was due to the synergistic cooperation between the P and N dopants, which could reduce the reaction barriers and was favorable for ORR and OER. Moreover, the Zn-air battery using Co-N-P 1.5 -MC as the cathode showed remarkable battery performance with high stability (could operate stably for over 160 h at 10 mA·cm −2 ) and maximum power density (119 mW·cm −2 ), demonstrating its potential for practical applications. This work could provide significant enlightenment towards the design and construction of bifunctional oxygen electrocatalyst for next-generation electrochemical devices.

The oxygen evolution reaction (OER) electrocatalysts, which can keep active for a long time in acidic media, are of great significance to proton exchange membrane water electrolyzers. Here, Ru-Co 3 O 4 electrocatalysts with transition metal oxide Co 3 O 4 as matrix and the noble metal Ru as doping element have been prepared through an ion exchange–pyrolysis process mediated by metal-organic framework, in which Ru atoms occupy the octahedral sites of Co 3 O 4 . Experimental and theoretical studies show that introduced Ru atoms have a passivation effect on lattice oxygen. The strong coupling between Ru and O causes a negative shift in the energy position of the O p-band centers. Therefore, the bonding activity of oxygen in the adsorbed state to the lattice oxygen is greatly passivated during the OER process, thus improving the stability of matrix material. In addition, benefiting from the modulating effect of the introduced Ru atoms on the metal active sites, the thermodynamic and kinetic barriers have been significantly reduced, which greatly enhances both the catalytic stability and reaction efficiency of Co 3 O 4 .

We have demonstrated the improved performance of oxygen evolution reactions（OER） using Au/nickel phosphide （Ni12P5） core/shell nanoparticles （NPs） underbasic conditions. NPs with a Ni12Ps shell and a Au core, both of which havewell-defined crystal structures, have been prepared using solution-based syntheticroutes. Compared with pure NiuP5 NPs and Au-Ni12P5 oligomer-like NPs, thecore/shell crystalline structure with Au shows an improved OER activity. Itaffords a current density of 10 mA/cm2 at a small overpotential of 0.34 V, in 1 MKOH aqueous solution at room temperature. This enhanced OER activity mayrelate to the strong structural and effective electronic coupling between thesingle-crystal core and the shell.

ABSTRACT Developing low‐cost and efficient catalysts for sustainable hydrogen (H2) production to the reliance on precious metal is an important trend in the future development of catalysts. Herein, a simple in‐situ one‐step hydrothermal strategy is employed to modify the outer layer of Ni3S2 crystals with amorphous MoS2 to construct core‐shell heterostructures and heterogeneous interfaces, which promotes the chemisorption of intermediates, including hydrogen and oxygen, and realizes the coupling enhancement of hydrogen‐evolution reaction (HER) and oxygen‐evolution reaction (OER) in alkaline water electrolysis process. In 1.0 M KOH electrolyte, the overpotentials of the electrodes are 78 mV (HER) and 245 mV (OER) at a current density of 10 mA cm−2, respectively. At the same time, the electrode has excellent stability for more than 100 h at a current density of 100 mA cm−2, due to the amorphous structure. In addition, when used as an anode and cathode to form an electrolyzer, a cell voltage of only 1.5 V is required to produce a current density of 10 mA cm−2. This study demonstrates that the constructed amorphous heterostructured interface synergistically promotes the dissociation of water and the adsorption of intermediates, providing a deep insight on how to accelerate the development of efficient catalysts. Developing low‐cost and efficient catalysts for sustainable hydrogen (H2) production is an important trend. Herein, a simple in situ one‐step hydrothermal strategy is employed to modify the outer layer of Ni3S2 crystals with amorphous MoS2 to construct core‐shell heterostructures and heterogeneous interfaces, which promotes the chemisorption of intermediates, including hydrogen and oxygen, and realizes the coupling enhancement of HER and OER in the alkaline water electrolysis process.

Density functional theory (DFT) simulations of the oxygen evolution reaction (OER) are considered essential for understanding the limitations of water splitting. Most DFT calculations of the OER use an acidic reaction mechanism and the standard hydrogen electrode (SHE) as reference electrode. However, experimental studies are usually carried out under alkaline conditions using the reversible hydrogen electrode (RHE) as reference electrode. The difference between the conditions in experiment and calculations is then usually taken into account by applying a pH-dependent correction factor to the latter. As, however, the OER reaction mechanisms under acidic and under alkaline conditions are quite different, it is not clear a priori whether a simple correction factor can account for this difference. We derive in this paper step by step the theory to simulate the OER based on the alkaline reaction mechanism and explain the OER process with this mechanism and the RHE as reference electrode. We compare the mechanisms for alkaline and acidic OER catalysis and highlight the roles of the RHE and the SHE. Our detailed analysis validates current OER simulations in the literature and explains the differences in OER calculations with acidic and alkaline mechanisms.

Mixed ionic and electronic conductor double perovskites are very promising oxygen electrode materials for solid oxide cell technology. However, understanding their specific kinetic mechanism is a fundamental preliminary step towards detecting the best reachable performance, optimising the operation conditions and the electrode architecture. Indeed, the contributions of different rate-determining steps can vary as a function of the working point. In this framework, after a detailed experimental campaign devoted to the study of SmBa 0.8 Ca 0.2 Co 2 O 5+ δ (SBCCO) oxygen electrode behaviour, the authors propose a theoretical analysis of oxygen reduction and oxygen evolution reaction paths that couples a preliminary study through equivalent circuit analysis with a physics-based model to predict the operation of SBCCO as a reversible oxygen electrode. Following a semi-empirical approach, the kinetics formulation was derived from thermodynamics and electrochemistry fundamental principles and was tuned on electrochemical impedance spectroscopy (EIS) spectra in order to retrieve the unknown kinetic parameters. The successful cross-checking of the simulated results with the experimental data obtained by direct current measurements validated the proposed model, here applicable in further works on full cells to simulate the SBCCO oxygen reversible electrode performance.

HighlightsThe crystal facets featured with facet-dependent physical and chemical properties can exhibit varied electrocatalytic activity toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) attributed to their anisotropy.The highly active exposed crystal facets enable increased mass activity of active sites, lower reaction energy barriers, and enhanced catalytic reaction rates for HER and OER.The formation mechanism and control strategy of the crystal facet, significant contributions as well as challenges and perspectives of facet-engineered catalysts for HER and OER are provided.The electrocatalytic water splitting technology can generate high-purity hydrogen without emitting carbon dioxide, which is in favor of relieving environmental pollution and energy crisis and achieving carbon neutrality. Electrocatalysts can effectively reduce the reaction energy barrier and increase the reaction efficiency. Facet engineering is considered as a promising strategy in controlling the ratio of desired crystal planes on the surface. Owing to the anisotropy, crystal planes with different orientations usually feature facet-dependent physical and chemical properties, leading to differences in the adsorption energies of oxygen or hydrogen intermediates, and thus exhibit varied electrocatalytic activity toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this review, a brief introduction of the basic concepts, fundamental understanding of the reaction mechanisms as well as key evaluating parameters for both HER and OER are provided. The formation mechanisms of the crystal facets are comprehensively overviewed aiming to give scientific theory guides to realize dominant crystal planes. Subsequently, three strategies of selective capping agent, selective etching agent, and coordination modulation to tune crystal planes are comprehensively summarized. Then, we present an overview of significant contributions of facet-engineered catalysts toward HER, OER, and overall water splitting. In particular, we highlight that density functional theory calculations play an indispensable role in unveiling the structure–activity correlation between the crystal plane and catalytic activity. Finally, the remaining challenges in facet-engineered catalysts for HER and OER are provided and future prospects for designing advanced facet-engineered electrocatalysts are discussed.

Developing stable and efficient electrocatalysts is vital for boosting oxygen evolution reaction (OER) rates in sustainable hydrogen production. High-entropy oxides (HEOs) consist of five or more metal cations, providing opportunities to tune their catalytic properties toward high OER efficiency. This work combines theoretical and experimental studies to scrutinize the OER activity and stability for spinel-type HEOs. Density functional theory confirms that randomly mixed metal sites show thermodynamic stability, with intermediate adsorption energies displaying wider distributions due to mixing-induced equatorial strain in active metal-oxygen bonds. The rapid sol-flame method is employed to synthesize HEO, comprising five 3d-transition metal cations, which exhibits superior OER activity and durability under alkaline conditions, outperforming lower-entropy oxides, even with partial surface oxidations. The study highlights that the enhanced activity of HEO is primarily attributed to the mixing of multiple elements, leading to strain effects near the active site, as well as surface composition and coverage. Efficient and durable electrocatalysts are essential for boosting oxygen evolution reaction toward hydrogen production. Here, the authors report a combined theoretical and experimental study on high-entropy spinel oxide with element mixing and strains providing superior activity and stability.

HighlightsSynthesis protocols, design engineering, theoretical calculations, and energy applications for metal–organic frameworks (MOFs)-derived electrocatalysts are systematically analyzed.Synthesizing methods of MOF-derived catalysts and their oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction electrocatalysis are discussed.The current status, ongoing challenges, and potential future outlooks of MOFs-derived electrocatalysts are highlighted.The core reactions for fuel cells, rechargeable metal–air batteries, and hydrogen fuel production are the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), which are heavily dependent on the efficiency of electrocatalysts. Enormous attempts have previously been devoted in non-noble electrocatalysts born out of metal–organic frameworks (MOFs) for ORR, OER, and HER applications, due to the following advantageous reasons: (i) The significant porosity eases the electrolyte diffusion; (ii) the supreme catalyst–electrolyte contact area enhances the diffusion efficiency; and (iii) the electronic conductivity can be extensively increased owing to the unique construction block subunits for MOFs-derived electrocatalysis. Herein, the recent progress of MOFs-derived electrocatalysts including synthesis protocols, design engineering, DFT calculations roles, and energy applications is discussed and reviewed. It can be concluded that the elevated ORR, OER, and HER performances are attributed to an advantageously well-designed high-porosity structure, significant surface area, and plentiful active centers. Furthermore, the perspectives of MOF-derived electrocatalysts for the ORR, OER, and HER are presented.

Dedicating to the exploration of efficient electromagnetic (EM) absorption and electromagnetic interference (EMI) shielding materials is the main strategy to solve the EM radiation issues. The development of multifunction EM attenuation materials that are compatible together EM absorption and EMI shielding properties is deserved our exploration and study. Here, the graphene-wrapped multiloculated NiFe 2 O 4 composites are reported as multifunction EM absorbing and EMI shielding materials. The conductive networks configurated by the overlapping flexible graphene promote the riched polarization genes, as well as electron transmission paths, and thus optimize the dielectric constant of the composites. Meanwhile, the introduction of magnetic NiFe 2 O 4 further establishes the magnetic-dielectric synergy effect. The abundant non-homogeneous interfaces not only generate effective interfacial polarization, also the deliberate multiloculated structure of NiFe 2 O 4 strengthens multi-scattering and multi-reflection sites to expand the transmission path of EM waves. As it turns out, the best impedance matching is matched at a lower filled concentration to achieve the strongest reflection loss value of −48.1 dB. Simultaneously, green EMI shielding based on a predominantly EM absorption and dissipation is achieved by an enlargement of the filled concentration, which is helpful to reduce the secondary EM wave reflection pollution to the environment. In addition, the electrocatalytic properties are further examined. The graphene-wrapped multiloculated NiFe 2 O 4 shows the well electrocatalytic activity as electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), which is mainly attributed to the interconnected structures formed by graphene and NiFe 2 O 4 connection. The structural advantages of multiloculated NiFe 2 O 4 expose more active sites, which plays an important role in optimizing catalytic reactions. This work provides an excellent jumping-off point for the development of multifunction EM absorbing materials, eco-friendliness EMI shielding materials and electrocatalysts.