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Hydrogen is considered a promising clean energy vector with the features of high energy capacity and zero-carbon emission. Water splitting is an environment-friendly and effective route for producing high-purity hydrogen, which contains two important half-cell reactions, namely, the anodic oxygen evolution reaction (OER) and the cathodic hydrogen evolution reaction (HER). At the heart of water splitting is high-performance electrocatalysts that efficiently improve the rate and selectivity of key chemical reactions. Recently, perovskite oxides have emerged as promising candidates for efficient water splitting electrocatalysts owing to their low cost, high electrochemical stability, and compositional and structural flexibility allowing for the achievement of high intrinsic electrocatalytic activity. In this review, we summarize the present research progress in the design, development, and application of perovskite oxides for electrocatalytic water splitting. The emphasis is on the innovative synthesis strategies and a deeper understanding of structure–activity relationships through a combination of systematic characterization and theoretical research. Finally, the main challenges and prospects for the further development of more efficient electrocatalysts based on perovskite oxides are proposed. It is expected to give guidance for the development of novel non-noble metal catalysts in electrochemical water splitting. [ABSTRACT FROM AUTHOR]

Energy crises, environmental pollution, and freshwater deficiency are critical issues on the planet. Electrolytic hydrogen generation from saline water, particularly from salt‐contained hazardous wastewater, is significant to both environment and energy concerns but still challenging due to the high energy cost, severe corrosion, and the absence of competent electrocatalysts. Herein, a novel strategy is proposed for energy‐efficient hydrogen production coupled with electro‐oxidation removal of ethanolamine pollutant in saline water. To achieve this, an active and durable heterostructured electrocatalyst is developed by in situ growing Ni@Ni3S2 core@shell nanoparticles in cross‐linked 3D carbon nanotubes' (CNTs) network, achieving high dispersibility and metallic property, low packing density, and enriched exposed active sites to facilitate fast electron/mass diffusion. The unique Ni@Ni3S2/CNTs nano‐heterostructures are competent for long‐term stably electro‐oxidizing environmental‐unfriendly ethanolamine at a high current density of 100 mA cm−2 in saline water, which not only suppresses oxygen and chloride evolution reactions but also decreases the energy consumption to boost hydrogen production. Associated with experimental results, density functional theory studies indicate that the collaborative adsorption of electrolyte ions and ethanolamine molecules can synergistically modulate the adsorption/desorption properties of catalytic active centers on Ni@Ni3S2/CNTs surface, leading to long‐term stabilized electrocatalysis for efficient ethanolamine oxidation removal and less‐energy hydrogen simultaneous production in saline water. [ABSTRACT FROM AUTHOR]

Highlights: B atoms modify the local electronic structure of Bi with positive valence sites. B doped Bi boosts highly efficient electroreduction of CO2 to formate. B dopant differentiates the proton participations in CO2 RR and HER processes. The dominant mechanistic pathway of B promoted formate generation is unraveled. Electrochemical reduction of CO2 to formate is economically attractive but improving the reaction selectivity and activity remains challenging. Herein, we introduce boron (B) atoms to modify the local electronic structure of bismuth with positive valence sites for boosting conversion of CO2 into formate with high activity and selectivity in a wide potential window. By combining experimental and computational investigations, our study indicates that B dopant differentiates the proton participations of rate-determining steps in CO2 reduction and in the competing hydrogen evolution. By comparing the experimental observations with the density functional theory, the dominant mechanistic pathway of B promoted formate generation and the B concentration modulated effects on the catalytic property of Bi are unravelled. This comprehensive study offers deep mechanistic insights into the reaction pathway at an atomic and molecular level and provides an effective strategy for the rational design of highly active and selective electrocatalysts for efficient CO2 conversion. [ABSTRACT FROM AUTHOR]

The performance of Sr2FeMoO6–σ double perovskites can be significantly enhanced by optimizing the ratio of Fe/Mo as a promising electrode material for solid oxide fuel/electrolysis cells. However, the intrinsic origin is still doubt for the improvement of Sr2FeMoO6–σ sluggish electrocatalytic reaction kinetics. Herein, their electronic structures are investigated by partial replacement of Mo with Fe ions. As the Fe content in Sr2Fe1+xMo1–xO6–δ is increased, its oxidation state increases, which enhances the metal–oxygen hybridization and shifts its bulk O p band energy toward the Fermi level. These electronic and structural variations decrease the O‐vacancy formation and migration energy, which, in turn, facilitates the formation of more oxygen vacancy defects and O ion transport, promoting the full contact between analytes and active B‐site transition metals and also the catalytic reaction kinetics. Consequently, the solid oxide cells with optimized Sr2Fe1.5Mo0.5O6–σ electrodes operating at 800 °C demonstrate high power density of 1.24 W cm−2 using H2 as fuel, and large CO2 electrolysis current density of 1.5 A cm−2 at 1.5 V, which are comparable with those of current state‐of‐the‐art Ni‐based catalysts. The findings provide a new understanding for the origin of the enhanced reaction kinetics of Sr2Fe1+xMo1–xO6–δ serial materials by increasing Fe doping. [ABSTRACT FROM AUTHOR]

The realization of large‐scale H2 production from electrocatalytic water splitting is severely impeded by the kinetically sluggish and economically less viable anodic oxygen evolution reaction. Here, an efficient strategy was established for the concurrent H2 production and oxidative alcohols refining into value‐added formate by utilizing self‐supported Ni2P−CoP bifunctional electrocatalysts. Benefiting from high intrinsic activity, abundant active sites, and synergistic promoting effects of bimetallic phosphides, the constructed two‐electrode electrolyzer required a cell voltage of around 1.3 V to achieve 10 mA cm−2, which is more than 200 mV lower than that of pure water splitting. Moreover, simultaneous productions of H2 with near‐unity conversion efficiency and formate at high faradaic efficiencies of 99.8 and 89.6 % oxidatively produced from methanol and glycerol, respectively, were achieved with excellent durability. This work presents a general and economic approach toward the fabrication of cost‐effective electrocatalysts for energy‐efficient and profitable large‐scale renewable energy integration. [ABSTRACT FROM AUTHOR]

The Co‐based electrocatalyst is among the most promising candidates for electrochemical oxidation of 5‐hydroxymethylfurfural (HMF). However, the intrinsic active sites and detailed mechanism of this catalyst remains unclear. We combine experimental evidence and a theoretical study to show that electrogenerated Co3+ and Co4+ species act as chemical oxidants but with distinct roles in selective HMF oxidation. It is found that Co3+ is only capable of oxidizing formyl group to produce carboxylate while Co4+ is required for the initial oxidation of hydroxyl group with significantly faster kinetics. As a result, the product distribution shows explicit dependence on the Co oxidation states and selective production of 5‐hydroxymethyl‐2‐furancarboxylic acid (HMFCA) and 2,5‐furandicarboxylic acid (FDCA) are achieved by tuning the applied potential. This work offers essential mechanistic insight on Co‐catalyzed organic oxidation reactions and might guide the design of more efficient electrocatalysts. [ABSTRACT FROM AUTHOR]

The development of highly efficient electrocatalysts toward the oxygen evolution reaction is imperative for advancing water splitting technology to generate clean hydrogen energy. Herein, a two dimensional (2D) nanosheet ammonium cobalt phosphate hydrate (NH4CoPO4·H2O) catalyst based on the earth‐abundant non‐noble metal is reported. When used for the challenging alkaline saline water electrolysis, the NH4CoPO4·H2O catalyst with the optimal thickness of 30 nm achieves current densities of 10 and 100 mA cm−2 at the record low overpotentials of 252 and 268 mV, respectively, while maintaining remarkable stability during the alkaline saline water oxidation at room temperature. X‐ray absorption fine spectra reveal that the activation of Co (II) ions (in NH4CoPO4·H2O) to Co (III) species constructs the electrocatalytic active sites. The 2D nanosheet morphology of NH4CoPO4·H2O provides a larger active surface area and more surface‐exposed active sites, which enable the nanosheet catalyst to facilitate the alkaline freshwater and simulated seawater oxidation with excellent activity. The facile and environmentally‐benign H2O‐mediated synthesis route under mild condition makes NH4CoPO4·H2O catalyst highly feasible for practical manufacturing. In comparison with noble metals, this novel electrocatalyst offers a cost‐effective alternative for economic saline water oxidation to advance water electrolysis technology. [ABSTRACT FROM AUTHOR]

Electrochemical nitrate reduction (NITRR) offers a promising alternative toward nitrogen recycling and ammonia production under ambient conditions, for which highly active and selective electrocatalyst is desired. In this study, metallic cobalt nanoarrays as facilely prepared from the electrochemical reduction of Co(OH)2 nanoarrays (NAs) are demonstrated to exhibit unprecedented NH3 producing capability from catalyzing NITRR. Benefitting from the high intrinsic activity of Co0, intimate contact between active species and conductive substrate and the nanostructure which exposes large number of active sites, the Co‐NAs electrode exhibits current density of −2.2 A cm−2 and NH3 production rate of 10.4 mmol h−1 cm−2 at −0.24 V versus RHE under alkaline condition and significantly surpasses reported counterparts. Moreover, the close‐to‐unity (≥96%) Faradaic efficiency (FE) toward NH3 is achieved over wide application range (potential, NO3− concentration and pH). Density function theory calculation reveals the optimized adsorption energy of NITRR intermediates on Co surface over Co(OH)2. Furthermore, it is proposed that despite the sluggish kinetics of Volmer step (H2O → *H + *OH) which provides protons in conventional hydrogenation mechanism, the proton‐supplying water dissociation process on Co surface is drastically facilitated following a concerted water dissociation–hydrogenation pathway. [ABSTRACT FROM AUTHOR]

Electrocatalysis plays a critical role in clean energy conversion, enabling great improvement for future sustainable technologies. Single atom catalysts (SACs) derived from metal–organic framework (MOF) are emerging extraordinary materials in electrochemical catalytic applications. Covering the merits of unique electronic structure, low‐coordination environment, quantum size effect, and metal–support interaction, SACs promise enhanced electrocatalytic activity, stability, and selectivity in the field of clean energy conversion. In this article, MOF synthesis routes to afford well‐dispersed SACs along with the respective synthesis mechanism are systematically reviewed first, and typical examples of each strategy are carefully discussed. Then the characterization techniques in understanding the isolated and spatial distribution, local electronic structure, coordination environment for SACs, and insights into stable mechanisms provided by density functional theory (DFT) calculations are summarized. In addition, several important electrocatalytic applications and electrocatalytic mechanisms of the MOF‐derived SACs, including for the oxygen reduction reaction, CO2 reduction reaction, nitrogen reduction reaction, hydrogen evolution reaction, oxygen evolution reaction, etc., are highlighted. To facilitate the future development of high‐performing SACs, several technical challenges and corresponding research directions are proposed. [ABSTRACT FROM AUTHOR]

Efficient electrocatalysts for the oxygen evolution reaction (OER) are highly desirable because of the intrinsically sluggish kinetics of OER. Herein, core–shell structured nanospheres of NiFexSn@NiFe (oxy)hydroxide (denoted as NiFexSn‐A) are prepared as active OER catalysts by a facile electrochemical strategy, which includes electrodeposition of NiFexSn alloy nanospheres on carbon cloth (CC) and following anodization. The alloy core of NiFexSn could promote charge transfer, and the amorphous shell of NiFe (oxy)hydroxide is defect‐rich and nanoporous due to the selective electrochemical etching of Sn in alkaline medium. The optimized catalyst of NiFe0.5Sn‐A displays a remarkable OER performance with a low overpotential of 260 mV to reach the current density of 10 mA cm−2, a small Tafel slope of 50 mV dec−1, a high turnover frequency of 0.194 s−1 at an overpotential of 300 mV, and a robust durability. Further characterizations indicate that the superior OER performance of the core–shell structured NiFe0.5Sn‐A nanospheres might originate from abundant active sites and small charge transfer resistance. This work brings a new perspective to the design and synthesis of core–shell structured nanospheres for electrocatalysis through a facile electrochemical strategy. [ABSTRACT FROM AUTHOR]

The sluggish kinetics of oxygen evolution reaction (OER) is the main bottleneck for the electrocatalytic water splitting to produce hydrogen (H2), and the by‐product is worthless O2. Therefore, designing a thermodynamically favorable oxidation reaction to replace OER and coupling with value‐added product generation on the anode is of significance for boosting H2 generation under low electrolysis voltage. Herein, cobalt hydroxide@hydroxysulfide nanosheets on carbon paper (Co(OH)2@HOS/CP) are synthesized as bifunctional electrocatalysts to facilitate H2 production and convert methanol to valuable formate simultaneously. Benefiting from the influences/changes on the composition, surface properties, electronic structure, and chemistry of Co(OH)2, the as‐obtained electrodes exhibit very high selectivity for methanol to value‐added formate oxidation (MFO) and boost electrocatalytic performance with low overpotential of 155 mV for MFO and 148 mV for hydrogen evolution reaction at a current density of 10 mA cm−2. Furthermore, the integrated two‐electrode electrolyzer drives 10 mA cm−2 at a cell voltage of 1.497 V with united 100% Faradaic efficiency for anodic and cathodic reaction and continuous 20 h of operation without obvious decay. The electrocatalytic hydrogen production with the assistance of alternative oxidation by the robust electrocatalyst can be further used to realize the upgrading of other organic molecules with less energy consumption. [ABSTRACT FROM AUTHOR]

Oxygen evolution reaction (OER) over perovskite oxides, upon undergoing a lattice oxygen oxidation mechanism, is strongly oxygen vacancy‐correlated as determined by the oxygen ion diffusivity. Despite substantial efforts having been devoted to tuning the oxygen vacancy concentration in perovskite oxides, the impact of the concomitant altering of oxygen vacancy ordering is often underestimated. In particular, the underlying mechanism of how the ordering and the concentration of oxygen vacancy affect the lattice OER, and how to well balance them still remain inadequately understood. Herein, a series of Sr1−xCaxCo0.5Fe0.5O3−δ with gradually increased oxygen vacancy concentration and ordering are synthesized. Theoretical calculations indicated that a higher oxygen vacancy concentration promoted the lattice oxygen migration, whereas a higher oxygen vacancy ordering impeded it. Particularly, Sr0.5Ca0.5Co0.5Fe0.5O3−δ with a relatively higher oxygen vacancy concentration and a lower ordering displayed the maximum oxygen diffusion rate and the optimal OER activity, affording a current density of 10 mA cm−2 at a quite low overpotential of 310.2 mV, together with a small Tafel slope of 55.87 mV dec−1. This study sheds light on the critical influence of oxygen vacancy configuration on the lattice OER, and paves a compromised avenue to screen and design advanced electrocatalysts for various electrochemical devices. [ABSTRACT FROM AUTHOR]

Electrochemical CO2 reduction reaction (CO2RR) holds a great potential for converting CO2 into valuable carbon‐based chemicals and fuels. A promising strategy for enhancing CO2RR performance is the deliberate structural design of electrocatalysts, which can maximize the utilization of inherent structural advantages. In this work, SnO2 nanocubes (NCs) and nanorods (NRs) are synthesized using a surface energy‐driven growth orientation method, where the stable (110) facet and the highly energetic (001) facet constitute the SnO2 nanostructures. Leveraging the inherent structural merits of different facets on SnO2, theoretical calculations reveal that the (001) facet plays a primary role in inhibiting hydrogen evolution reaction (HER), while both (110) and (001) facets are highly favorable for CO2‐to‐formate conversion under the external bias. As a result, SnO2 NCs with a higher facet ratio of (001)/(110) achieve nearly 100% selectivity for the formation of carbonaceous products during CO2RR. More importantly, a maximum partial current density of about 1 A cm−2 with a formate Faradaic efficiency (FE) of over 90% is achieved in a flow cell, distinguishing it from most of the reported Sn‐based electrocatalysts. These results highlight the strategic advantages of leveraging the inherent structure of nanomaterials for efficient CO2RR. [ABSTRACT FROM AUTHOR]

NiFe x P@NiCo-LDH/CC nanosheet core-shell nanoarrays electrocatalysts are prepared by electrodeposition and phosphating methods for relatively low potential production of H 2 and value-added formate in methanol/water electrolysis systems. During the oxygen evolution reaction process, the over potential is 269 mA at the current density of 50 mA cm−2 and the Tafel slope is 97 mV dec−1. It also realizes the stable long-term electrocatalysis of methanol to formate under high current density and maintains a relatively high Faraday efficiency of 100%. Meanwhile, the energy saving is higher than 10% in the methanol oxidation and co-hydrogen production system that achieves great attention. The superior performance of NiFe x P@NiCo-LDH/CC bifunctional electrocatalysts might be beneficial from the interaction to Ni and Fe bimetallic extranuclear electrons that exposes more active sites. A highly active electrocatalyst NiFe x P@NiCo-LDH/CC is synthesized by a simple electrochemical deposition method. The catalyst has excellent catalyst activity because of the synergistic effect of Ni and Fe, and abundant active sites. The selectivity of the methanol oxidation reaction is high and the product is value-added formate. [Display omitted] • NiFe x P@NiCo-LDH was prepared using a simple electrochemical deposition method. • The NiFe x P@NiCo-LDH exhibits superior electrocatalytic activity and long-term stability. • The selectivity of the methanol oxidation reaction is high and the product is value-added formate. • The catalyst shows excellent catalyst activity because of the synergistic effect of Ni and Fe and abundant active sites. [ABSTRACT FROM AUTHOR]

Designing anodic electrocatalysts with high activity and robust stability for acidic oxygen evolution reaction (OER) is significant for the large-scale promotion of sustainable proton exchange membrane water electrolysis (PEMWE). Most reported Ru-based electrocatalysts tend to further improve activity at the expense of stability. Herein, we report the synthesis of crystalline Mn 3 O 4 supported Ru-RuO 2 nano-heterostructures as the anodic electrocatalyst that only requires a low overpotential of 182 mV (10 mA cm−2) for acidic OER, accompanied with a record stability of 400 h in 0.5 M H 2 SO 4. The results of XPS, ICP-MS, and XAS indicate that the Mn 3 O 4 substrate plays a crucial role in stabilizing Ru-RuO 2 nano-heterostructure by preventing Ru from over-oxidation and dissolution. Meanwhile, DEMS with isotope labeling reveals that the Ru-RuO 2 nano-heterostructure contributes to suppressing lattice oxygen oxidation mechanism (LOM) and concurrently expediting the involvement of adsorbate evolution mechanism (AEM) for boosting the acidic OER performance. [Display omitted] • The constructed Ru-RuO 2 /Mn 3 O 4 /CP only requires a low overpotential of 182 mV (10 mA cm−2) in 0.5 M H 2 SO 4. • Long-term stable acidic oxygen evolution reaction (400 h) is achieved in a membrane-free electrolyzer. • Experimental studies demonstrate that the Mn 3 O 4 substrate can protect Ru sites from over-oxidation and dissolution. • The modulation of OER pathways is deeply investigated by the experimental and calculation results. • It successfully brings about an effective strategy to maintain active Ru sites on the Mn 3 O 4 substrate. [ABSTRACT FROM AUTHOR]

A novel electrocatalyst of ZnS anchored on an N,S-codoped carbon support (ZnS/NSC-NaCl) is fabricated via a vulcanization-assisted methodology. ZnS/NSC-NaCl is used for highly efficient oxygen reduction reaction and Al-air battery. [Display omitted] The development of non-precious based oxygen reduction reaction (ORR) catalysts with outstanding catalytic performance is desirable but still a grand challenge for practical Al-air battery. Herein, we report a vulcanization-assisted pyrolysis strategy for creating zeolitic imidazolate framework-derived catalysts with a N, S co-doped carbon support and highly exposed ZnS and Zn-N x sites. The trithiocyanuric acid (TCA) is found not only to introduce S into the carbon derived from ZIF-8 and ZnS to adjust the electronic structure of carbon matrix during the pyrolysis, but also result in a shrinkage of carbon framework with a hierarchical porous structure. Such an architecture boosts abundant active sites exposed and accelerates remote mass transportation. As a result, the optimized 3.5ZnS/NSC-NaCl-900 delivers an impressive enhanced performance toward ORR in alkaline medium with a high half-wave potential of 0.905 V (vs. reversible hydrogen electrode), which is superior to most of non-precious metal-based catalysts. Density functional theory calculations unveil that the ZnS in 3.5ZnS/NSC-NaCl-900 can effectively lower the Gibbs energy barrier of crucial steps and therefore promotes the reaction kinetics. Furthermore, 3.5ZnS/NSC-NaCl-900 also displ ays greater power density and specific capacity than Pt/C in Al-air batteries. [ABSTRACT FROM AUTHOR]

Porous boron-bearing Fe-nitrogen doped carbon electrocatalysts (Fe-BNC) are prepared by pyrolysis treatment of Fe/B co-doped zeolitic imidazolate frameworks (ZIFs). The as-obtained Fe-BNC catalysts with a high surface area (1300 m2 g−1) favor a 4-electron reduction pathway for efficient oxygen reduction reaction (ORR). The Fe-BNC catalysts demonstrate a half-wave potential of ∼0.85 V vs RHE comparable to that of Pt/C catalyst and high stability in 0.1 M KOH. The dopant of little boron and iron into nitrogen-doped carbon results in the high surface area, enhanced surface polarities, electronic properties and exposing more active sites to introduce a synergistic effect for enhanced ORR performance. Moreover, Fe-BNC electrocatalysts used as air cathode for Al-air batteries exhibit a high peak power density of 195.2 mw cm−2 and excellent stability even after discharging for 24 h at room temperature, revealing an excellent performance in application of metal-air batteries and other energy converting devices. Porous boron-bearing Fe-nitrogen doped carbon electrocatalysts (Fe-BNC) with low loading of Fe and B species prepared by pyrolysis treatment demonstrate efficient electrocatalytic oxygen reduction and excellent metal-air battery performance. [Display omitted] • The Fe-BNC is successfully fabricated by a facile chemical doping method. • The ZIF structure is maintained even after high temperature pyrolysis process. • The Fe-BNC catalyst displays high ORR activity and stability. • It confirms the incorporating of B, Fe into N -doped carbon improves ORR activity. • The Fe-BNC as electrode for Al-air battery also delivers excellent performance. [ABSTRACT FROM AUTHOR]

Electrochemical nitrate reduction (NITRR) offers a promising alternative toward nitrogen recycling and ammonia production under ambient conditions, for which highly active and selective electrocatalyst is desired. In this study, metallic cobalt nanoarrays as facilely prepared from the electrochemical reduction of Co(OH)2 nanoarrays (NAs) are demonstrated to exhibit unprecedented NH3 producing capability from catalyzing NITRR. Benefitting from the high intrinsic activity of Co0, intimate contact between active species and conductive substrate and the nanostructure which exposes large number of active sites, the Co‐NAs electrode exhibits current density of −2.2 A cm−2 and NH3 production rate of 10.4 mmol h−1 cm−2 at −0.24 V versus RHE under alkaline condition and significantly surpasses reported counterparts. Moreover, the close‐to‐unity (≥96%) Faradaic efficiency (FE) toward NH3 is achieved over wide application range (potential, NO3− concentration and pH). Density function theory calculation reveals the optimized adsorption energy of NITRR intermediates on Co surface over Co(OH)2. Furthermore, it is proposed that despite the sluggish kinetics of Volmer step (H2O → *H + *OH) which provides protons in conventional hydrogenation mechanism, the proton‐supplying water dissociation process on Co surface is drastically facilitated following a concerted water dissociation–hydrogenation pathway. [ABSTRACT FROM AUTHOR]

Exploring noble-free electrocatalyst for hydrogen evolution by electrolysis of water is significant. Herein, porous Ni(OH) 2 @Ni spherical particles are electrodeposited on carbon papers as efficient electrocatalysts for hydrogen evolution reaction (HER) from water. Due to the porous and composite structure, the HER activity of Ni(OH) 2 @Ni/CP is better than the single phase Ni or Ni(OH) 2 particles on the carbon paper. The overpotential of Ni(OH) 2 @Ni/CP is 106 mV at the current density of 10 mA cm−2 and the Tafel slope is 88 mV dec−1. Moreover, the stability of the catalysts tested for 12 h is also good for HER. Furthermore, the small R ct (1.65 Ω) of Ni(OH) 2 @Ni/CP provides the evident for its excellent catalytic performance. The method of electrodeposition provides the controllable uniform size for porous spherical Ni(OH) 2 @Ni particles. Moreover, the Faradaic efficiency for hydrogen evolution is 100%. Image 1 • The overpotential of Ni(OH) 2 @Ni/CP is 106 mV (10 mA cm−2). • The Tafel slope is 88 mV dec−1 and the stability are good for 12 h. • One-pot preparation of Ni(OH) 2 @Ni/CP via through cyclic voltammetry (CV). [ABSTRACT FROM AUTHOR]

[Display omitted] • Facile fabrication of IrO x -MoO 3 nano-heterostructure on Ti mesh. • Low Ir content, high acidic OER activity and stability of c-IrO x -MoO 3 /Ti electrode. • Highly dispersive IrO x nanoparticles related to intertwined MoO 3 sheets. • Optimized absorption energies of oxygen intermediates on active sites from electronic interaction of IrO x -MoO 3 heterostructure. Rational design of Ir-based electrocatalyst with high performance and low cost remains as an urgent requirement to speed up the sluggish acidic water oxidation to produce hydrogen in renewable energy conversion and storage systems. In this work, the highly dispersed IrO x nanoparticles are fabricated on MoO 3 sheets coated Ti meshes (c-IrO x -MoO 3 /Ti) as efficient electrocatalytic electrodes for acidic water oxidation. The heterogeneous c-IrO x -MoO 3 /Ti catalysts show much higher acidic oxygen evolution reaction activity (∼200 mV overpotentials at 10 mA cm−2) and long-term stability (longer than 130 h at 100 mA cm−2) with extremely low Ir content (∼28.35 μg Ir cm−2) as compared to the IrO x /Ti and commercial IrO 2 catalysts. The special intertwined formation of MoO 3 sheets through electrodeposition effectively promotes the uniform dispersion of IrO x nanoparticles and the electrocatalytic performance. Theoretical calculations reveal that the electronic modulation on the MoO 3 -IrO x heterogeneous interface optimized the adsorbed energies for oxygen intermediates on the active Ir sites of the catalysts. The self-assembled proton exchange membrane single-cell electrolyzer test further verifies that the fabricated c-IrO x -MoO 3 /Ti catalysts demonstrate a greatly lower voltage and higher stability for water electrolysis than the commercial IrO 2 catalysts. This work provides a new pathway to designing highly active and acid-resistant Ti-supported water oxidation catalysts with ultra-low Ir content. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) plays a significant role in energy conversion technologies such as metal-air batteries and fuel cells. The development of efficient ORR electrocatalyst is highly desirable to achieve the fast oxygen reduction. In this work, the bimetallic Cu and Co embedded nitrogen-doped carbon (CuCo-N/C) is fabricated as efficient electrocatalyst for ORR. The incorporation of Cu-precursor into Co-based zeolitic imidazolate frameworks (ZIF) is innovated here to synergistically enhance the activity of Co. Surprisingly, the addition of Cu can also increase the nitrogen content in the CuCo-N/C catalysts, which could generate more active sites and result in the improvement of ORR activity. The optimized CuCo-N/C catalysts exhibit superior ORR performance with a half-wave potential of 0.85 V (vs. RHE), a limiting current density of 5.61 mA cm−2 and enhanced long-term durability comparing with the state-of-the-art Pt/C catalysts. Benefiting from the unique structure, the as-made CuCo-N/C catalysts as electrode for Zn-air battery delivers excellent performance with a peak power density of 66.9 mW cm−2, a high open circuit voltage of 1.468 V, and a voltage degradation of about 1.4% after 12 h discharging, which is much better than that of Pt/C catalysts. • A CuCo-N/C catalyst is obtained by a fast and efficient microwave-assisted method. • High N content and bimetallic Cu/Co contribute to the enhanced ORR performance. • The CuCo-N/C electrode delivers excellent performance in Zn-air battery. [ABSTRACT FROM AUTHOR]

The development of efficient, stable and low-cost bifunctional oxygen electrocatalysts is critical to the realization of practically viable rechargeable Zn-air batteries. Herein, we report a strongly cooperative spinel nanohybrid as a promising air electrode catalyst for rechargeable Zn-air batteries. Ultrafine sub-10 nm MnFe 2 O 4 crystals are in situ grown on the ultrathin NiCo 2 O 4 nanosheets, leading to a highly effective surface area and a strong synergistic chemical coupling effect. The distinct architecture and complex composition endow an excellent bifunctional oxygen electrocatalytic activity in alkaline condition. The practical rechargeable Zn-air battery with the hybrid electrocatalyst demonstrates a high round-trip efficiency (a low discharge-charge voltage gap of 0.81 V at a reversible current density of 10 mA cm −2 ) and an outstanding durability, which outperforms the commercial Pt/Ru/C electrocatalyst. The resulting hybrid (MnFe 2 O 4 /NiCo 2 O 4 ) shows great promise as an alternative bifunctional electrocatalyst to the precious metals for the application in Zn-air batteries. [ABSTRACT FROM AUTHOR]

Extensive research has been devoted to the development of advanced oxygen reduction reaction (ORR) catalysts with functionally diverse active sites. Herein, we show a smart approach to advancing the ORR catalytic activity of a 3D porous perovskite. The facile oxidative-reductive-oxidative (O-R-O) thermal treatment cycle executed on Ag doped LaFeO 3 could stepwise switch on three different reaction sites (exsolved Ag-NPs, oxygen deficiency and Fe 4+ with optimal electron configuration) for ORR. Detailed characterizations illustrate that the ORR activity is basically derived from the hierarchically porous scaffold which provides a large surface area and enough pore volumes for mass and ion diffusion. More importantly, the unique synergistic effects among three separate kinds of reaction sites endow the speed-up of oxygen adsorption, activation and O 2− transportation. The exemplified results set out new design principles for the optimization of alternative catalysts. [ABSTRACT FROM AUTHOR]

NiCo x P @ NiCo-LDH catalysts are prepared by phosphating NiCo nanosheets on NiCo-layered double hydroxide (LDH) with multi-layer heterostructure. The NiCo x P @ NiCo-LDH could undergo electrocatalytic hydrogen evolution from the methanol/water mixture and value-added formate co-production. During the electrocatalytic reactions, the phosphating NiCo x P nanosheets could greatly improve the electron transfer efficiency, and it has a synergistic effect with heterostructures to enhance the electrocatalytic performance. During the hydrogen evolution and methanol oxidation reactions, the potential is only 0.132 and 1.23 V when the current density reaches 10 mA cm−2. Meanwhile, the NiCo x P @ NiCo-LDH symmetric two-electrode electrolyzer has a lower potential of only 1.43 V at a current density of 10 mA cm−2 and the Faraday efficiency of the production of formate and H 2 is nearly 100%. The electrocatalysts also display excellent stability during the water/methanol co-electrolysis. [Display omitted] • NiCo x P @ NiCo-LDH was prepared using a simple electrochemical deposition method. • The NiCo x P @ NiCo-LDH exhibits superior electrocatalytic activity and long-term stability. • The selectivity of the methanol oxidation reaction is high and the product is value-added formate. • The catalyst shows excellent catalyst activity because of the synergistic effect of Ni and Co and abundant active sites. [ABSTRACT FROM AUTHOR]

Surface re-construction was a common phenomenon for non-oxide compound electrocatalysts in anodic oxidation reaction in alkaline electrolyte but surface deactivation arising from excessive oxidation/hydroxylation was critical hindrance to the long-term stability. Herein, a unique anode-cathode interchangeable electrocatalysis strategy is proposed for methanol upgrading reaction (MUR) and hydrogen co-generation in membrane-free electrolyzer. A periodical electrolysis is taken place for the Ni 3 S 2 /CNTs electrode at positive/negative currents over time. Compared with the traditional chronopotentiometry mode, the MUR-HER coupled reactions by periodically switching anode/cathode per hour present an excellent long-term stability at high current densities of ± 100 mA cm−2, in which the Faradaic efficiencies for both H 2 and value-added formate are greater than 95%. Substantial experimental results and deep theoretical DFT studies signify that the successful application of this strategy is mainly due to the reversible modulation of oxidation/hydroxylation status on Ni 3 S 2 surface, which effectively prevent the surface active structures of electrocatalysts from over-oxidation. [Display omitted] • A periodical electrolysis is taken place with Ni 3 S 2 /CNTs electrode at positive or negative current over time. • Long-term stable methanol upgrading and hydrogen co-generation are achieved in a membrane-free electrolyzer. • Substantial XPS, XAFS and DFT studies indicate that the surface critical active sites can be in situ revived. • Such unique anode-cathode interchangeable strategy effectively prevents catalyst surface from over-oxidation. • It successfully brings about the reversible modulation of oxidation/hydroxylation status on Ni 3 S 2 surface. [ABSTRACT FROM AUTHOR]

• Binder-free electrode is obtained by a dip coating and calcination two-step method. • Ultrasmall Bi nanoparticles are confined in the in‐situ‐formed carbon nanosheets. • High durability is achieved at a remarkable high current density for nearly 40 h. • The electrode exhibits excellent CO 2 RR activity in a synergistic way. • PVP-derived carbon nanosheet facilitate interface charge-transfer capability. Developing high-efficient and durable electrocatalysts for CO 2 electroreduction reaction (CO 2 RR) at high current density is attractive but still challenging. In this study, ultrasmall Bi nanoparticles confined in carbon nanosheets are successfully prepared by directly annealing of dipped carbon cloth. Benefited from the uniform distribution of the ultrasmall Bi nanoparticles and the in‐situ‐formed carbon nanosheets, the resultant self-supported electrocatalysts exhibit excellent CO 2 RR activity in a synergistic way. The optimized Bi-PVP/CC600 exhibits high formate faradaic efficiency of over 81 % at high current densities in a wide potential range. Impressively, high durability is also achieved for this binder-free electrode, with a remarkable high current density of 54 mA∙cm−2 for nearly 40 h. The high performance associated with this facile and potentially scalable synthetic method suggests the great application potential of ultrasmall Bi nanoparticles in CO 2 RR. The strategy developed herein is versatile and can be extended to prepare other high‐performance ultrasmall metal nanoparticles catalysts. [ABSTRACT FROM AUTHOR]

• Ni(OH) 2 nanosheet arrays were formed on nickel foam spontaneously by a simple method. • Energy consumption of H 2 production was reduced via methanol-water electrolysis. • The oxidation product of methanol on the Ni(OH) 2 /NF was formic acid instead of CO 2. • The value-added formate and H 2 could be co-produced efficiently. Ni(OH) 2 nanosheet arrays are in situ prepared on Ni foam through very straightforward ultrasonication in HCl solution and the following rinsing and drying procedures. Value-added formate and hydrogen could be co-produced by selective oxidation of methanol without carbon dioxide emissions and water reduction over Ni(OH) 2 nanosheet arrays bifunctional electrocatalysts. Energy depletion for hydrogen evolution from water could be reduced by integrating with selective methanol oxidation rather than oxygen evolution. The prepared Ni(OH) 2 nanosheet arrays exhibits high activity for selective methanol oxidation in alkaline methanol-water solution. It gives a low potential of only 1.36 V (vs. reversible hydrogen electrode) to drive the current density of 100 mA cm−2. The faradaic efficiencies of formate are approximately 100% with the current densities from 10 mA cm−2 to 100 mA cm−2. Moreover, it is easy to separate the anodic and cathodic products without help of any membrane, which greatly simplifies the electrolysis system. [ABSTRACT FROM AUTHOR]

Solid oxide cells (SOCs) including solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs) are advanced electrochemical energy storage and conversion devices. However, the lack of highly active and stable fuel electrode materials impedes their practical applications. Herein, in-situ exsolved CoFe nanoparticles on perovskite matrixes with abundant defects are developed as bifunctional fuel electrocatalysts for SOCs from the Sr 2 FeMo 1-x Co x O 6−δ (x = 0, 0.15, 0.25, 0.45) precursor. Increasement of Co doping promotes CoFe alloy exsolution and the formation of more defects in the remaining perovskite matrix under reducing atmosphere at high temperatures. Consequently, with increasing Co dopant content, the electrocatalytic activity towards CO 2 electrolysis and hydrogen (H 2) fuel oxidation are both significantly enhanced for the reduced Sr 2 FeMo 1-x Co x O 6−δ. The reduced Sr 2 FeMo 1-x Co x O 6−δ with high Co doping content of x = 0.45 electrocatalysts also exhibits respectable coking resistance and excellent long-term stability. The high performance may be owing to the unique simultaneously in-situ formed nanoalloy-oxide heterostructure and electron-ion mixed conductive perovskite matrixes with abundant defects. Image 1 • Co doping promotes phase evolution and CoFe nanoparticles exsolution. • Phase evolution and CoFe exsolution facilitate the formation of oxygen vacancy defects. • Oxygen vacancy defects enhances the CO 2 adsorption and charge transfer processes. • The electrocatalytic activity for CO 2 electrolysis and H 2 oxidation is improved. [ABSTRACT FROM AUTHOR]

Design and synthesis of multi-functional electrocatalysts with high efficiency and low cost to replace noble metals are significantly important to realize new energy technologies. Herein, we report CuCo 2 S 4 hollow nanoneedle arrays as efficient trifunctional electrocatalysts for overall water splitting and aluminium-air batteries. CuCo 2 S 4 hollow nanoneedle arrays are grown on Ni foam (NF) via a facile hydrothermal method. Benefiting from the porous and hollow structure to expose more active sites, the CuCo 2 S 4 /NF hollow nanoneedle arrays exhibit superior electrocatalytic performance for hydrogen evolution (HER), oxygen evolution (OER), oxygen reduction reactions (ORR) in alkaline electrolytes. The corresponding experimental HER and OER overpotentials of CuCo 2 S 4 /NF catalyst are 61 mV and 189 mV at 10 mA cm−2 in 1.0 M KOH. In an assembled primary Al-air battery, the CuCo 2 S 4 /NF catalysts demonstrate an outstanding peak power density of 160 mW cm−2. This work provides a new strategy for developing non-noble metal multiple-functional catalysts for energy conversion and energy storage devices. Image 1 • Hollow nanoarrays copper-cobalt intermetallic sulfide on Ni foam are synthesized. • CuCo 2 S 4 exhibit synergistic electrocatalytic activity for HER, OER and ORR. • Al-air batteries self power the two-electrode configuration during water splitting. [ABSTRACT FROM AUTHOR]

• 'Nanoplatelet-on-nanoarray' electrocatalyst is obtained from MOF nanoarrays. • The Electrochem-assisted transformation greatly increases the surface active sites. • Synergy between Ni/Co and unique structure contribute to superior anodic activity. • The electrode shows universal robustness towards oxidation of organic molecules. • HMF and bio-glycerol are upgraded to value-added FDCA and formate with high FE. Replacing oxygen evolution reaction with thermodynamically more favorable organic oxidation reactions is considered as attractive approach to enhance the energy conversion efficiency in electrochemical water splitting. Herein, 'Nanoplatelet-on-Nanoarray' NiCo hydroxide-based electrocatalysts (t-NiCo-MOF) fabricated from the facile transformation of bimetallic metal-organic framework nanoarrays is reported to exhibit rich surface active sites and unprecedented activity towards the oxidation of organic molecules including 5-hydroxymethylfurfural, urea, methanol and glycerol. Benefitting from the synergy between Ni/Co and unique nanostructure which facilitates the charge and mass transfer, the optimal electrode exhibits current densities of 600∼730 mA/cm2 at 1.4 V vs RHE and the Tafel slopes are in the range of 35∼58 mV/dec depending on the oxidized species. Value-added chemicals such as 2,5-furandicarboxylic acid and formate are produced from HMF and methanol/glycerol (main constituents of 'bio-glycerol') with high FE and superior stability, demonstrating its promises in high-throughput electrochemical biomass upgrading. [ABSTRACT FROM AUTHOR]

Theoretical calculations prove that the Sn 3 O 4 lowers the activation barrier of producing HCOOH benefitting from moderate adsorption energies of intermediates (HCOO* and *H) among SnO, SnO 2 and Sn 3 O 4. As a result, a faradic efficiency for carbonaceous products over 97.7 % at −0.9 V RHE is obtained on the Sn 3 O 4 electrocatalyst. This combination of rigorous experimental and theoretical studies clearly elucidates the advantages of Sn 3 O 4 and sheds light on the rational design of SnO x -based electrocatalysts with special electronic structure for efficient CO 2 RR utilizations. • DFT calculations are performed to decipher the behaviors of SnO, SnO 2 and Sn 3 O 4 toward electroreduction of CO 2. • Sn 3 O 4 possesses the lowest activation barrier for the formation of HCOOH. • Flower-like Sn 3 O 4 delivers a FE carbonaceous of 97.7% and a partial current density of 16.6 mA/cm2 at −0.9 V RHE. • An onset overpotential of 190mV, the lowest reported thus far, is achieved on Sn 3 O 4. • The up-shifted electronic structure of Sn 3 O 4 plays an essential role for the boosted production of carbonaceous products. The catalytic performance of electrocatalyst on carbon dioxide reduction reaction (CO 2 RR) heavily depends on the adsorption strength of intermediates and electronic structure. For the first time, Sn 3 O 4 is identified as the most effective electrocatalyst for CO 2 RR among SnO x -based materials towards carbonaceous products by density functional theory calculation and experimental work. An optimized adsorption strength of intermediates is achieved on Sn 3 O 4 owing to the originally synergistic Sn2+ and Sn4+ effect resulted from the unique electronic structure of Sn 3 O 4. Additionally, with an up-shifted band structure, Sn 3 O 4 imparts the moderate adsorption energies of *H and HCOO* intermediate, which suppresses the hydrogen evolution reaction and promotes the intrinsic catalytic efficiency of CO 2 RR. The synthesized Sn 3 O 4 electrocatalyst delivers a carbonaceous faradic efficiency of ∼97.7% with a partial current density of 16.6 mA/cm2 at −0.9 V RHE. The corresponding overpotential of 190 mV is lower than the values from most of the reported SnO x -based electrocatalysts. [ABSTRACT FROM AUTHOR]

FeCo nanoparticles wrapped in N-doped carbon is developed as efficient oxygen reduction electrocatalysts for Al-air batteries • N-doped graphitic carbon embedded with FeCo nanoparticles has been prepared. • The PD-800 is an efficient ORR catalyst and comparable with Pt/C. • Al-air battery for PD-800 surpasses that of Pt/C catalyst. Developing highly active and durable electrocatalysts with low-cost for the oxygen reduction reaction (ORR) is of paramount importance for promoting economical and high-performance Al-air batteries. Herein, nitrogen-doped carbon decorated with FeCo nanoparticles catalysts is prepared by a low-cost and facile approach employed Prussian blue analogue and dicyandiamide as precursors. The obtained catalyst exhibits remarkable ORR activity with an onset potential (0.981 V vs. RHE) and a high half-wave potential (0.848 V vs. RHE), as well as superior stability in alkaline conditions. The outstanding electrocatalytic performance of electrocatalysts might be resulted from the hierarchical porous structure and synergetic effect between FeCo alloy and N-doped graphitic carbon species. As a demonstration, the optimized catalysts are employed as the cathode catalysts in a Al-air battery, which shows remarkable discharge performance with higher open-circuit voltage of 1.67 V and large power density of 98.62 mW cm−2 which exceeding commercial Pt/C electrocatalysts (1.65 V, 90.81 mW cm−2), and exceptional cycle stability of 40 h (4 cycles). This work will provide a chance to explore scalable advanced catalysts in Al-air battery. [ABSTRACT FROM AUTHOR]

Anode materials with excellent catalytic activity, good stability, and enhanced tolerance to carbon deposition are highly desired for solid oxide fuel cells (SOFCs). Herein, CoFe (CF) nanoalloy catalysts are homogeneously in-situ embedded on Sr 3 FeMoO 7 (RP-SFM) efficient electrically conductive perovskite matrix through reduction of Sr 2 FeMo 2/3 Co 1/3 O 6−δ precursor. The particle size of CoFe alloy is in the range of 10–50 nm, and the electrical conductivity enhances from about 8 to 17 S cm−1 to 49-63 S cm−1 after Sr 2 FeMo 2/3 Co 1/3 O 6−δ reduction. The maximum power density of SOFCs with the RP-SFM@CF-SDC(Sm 0.2 Ce 0 · 8 O 1.9) composite anode in H 2 fuel reaches to 2.12 W cm−2 at 850 °C, which is about 1.4 times than that of the SOFCs with traditional Ni-SDC anode. Moreover, the RP-SFM@CF-SDC anodes also demonstrate excellent resistance to carbon deposition and high power density when C 3 H 8 hydrocarbon is used as fuel. The improved catalytic activity results from the efficient electronic/ion conductive paths, abundant CoFe active sites, together with the enlarged trip phase boundaries (TPBs). Image 1 • CoFe(CF) nanoalloy are homogeneously embedded on the layered perovskite RP-SFM. • RP-SFM@CF anode exhibits excellent catalytic activity and good structural stability. • RP-SFM@CF-SDC anode exhibits higher electrochemical performance than Ni-SDC. • The improved performance results from the abundant CoFe active sites and TPBs. [ABSTRACT FROM AUTHOR]