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The bulk Ni/Fe ratio is a crucial parameter that determines the catalytic performance of the NiFe alloys by affecting the surface Fe/Ni ratio and the oxygen vacancy (O V) content, and the Ni 4 Fe 1 alloy with well-tailored oxide/metal interface presents highly enhanced oxygen evolution reaction with an overpotential of 242 mV at 10 mA cm−2 and a small Tafel slope of 37 mV dec−1. [Display omitted] NiFe alloys are among the most promising electrocatalysts for oxygen evolution reaction (OER). However, a comprehensive study is yet to be done to reveal the surface structure-performance relationship of NiFe alloys. In particular, the role of the ultrathin surface oxide layer, which is unavoidable for pure NiFe alloys, is always neglected. Herein, a series of NiFe alloys with different Ni/Fe ratios are fabricated. It is found that different Ni/Fe ratios lead to significant differences in surface composition and structure of the NiFe alloys, and thus affect their catalytic performance. Then, the oxide/metal interface of the Ni 4 Fe 1 alloy is tailored by adjusting the hydrogenation temperature to further understand the surface structure-activity relationship, and the optimal OER performance is achieved at the oxide/metal interfaces that have suitable surface Fe/Ni ratio and an appropriate amount of oxygen vacancies. In - situ Raman characterization shows that the Ni 4 Fe 1 alloy with well-tailored oxide/metal interface facilitates the formation of active species. Density functional theory calculations demonstrate that the ultrathin surface oxide layers are responsible for the high catalytic activity of the NiFe alloys, and that the quantity of oxygen vacancies in the surface oxides affects the adsorption energy of O* and thus to a great extent determines the catalytic activity. [ABSTRACT FROM AUTHOR]

Intercalation-induced partial exfoliation of NiFe LDHs with tunable interlayer space has been achieved by a scalable synthesis method, and the optimal NiFe LDHs show an overpotential of 225 mV at 10 mA cm−2 and a small Tafel slope of 43 mA dec−1. [Display omitted] Edge sites and interlayer space of NiFe layered double hydroxides (LDHs) play an important role in water oxidation. However, the combined effect of interlayer expansion and partial exfoliation on the catalytic activity is yet to be investigated. Herein, scalable synthesis of partially exfoliated citrate-intercalated NiFe LDHs with tunable interlayer space have been achieved. The effect of citrate concentration on the phase, morphology, surface elemental composition, electronic states of surface metals, and electrochemical properties are comprehensively studied. The unique structure results in improved intrinsic catalytic activity and abundant active edge sites for oxygen evolution reaction. The optimal NiFe LDHs show an overpotential of 225 mV at 10 mA cm−2, which is much smaller than that (∼305 mV) of the single-layer NiFe LDH nanosheets reported in the literature. The high catalytic activity can be mainly attributed to the combined effect between the enlarged interlayer space and the partial exfoliation/nanosheet thickness. That is, the interlayer space is related to the reaction kinetics/mechanism, while the degree of exfoliation affects the magnitude of the current density at a certain potential. [ABSTRACT FROM AUTHOR]

Synergistic composite catalysts have always been the research focus of water splitting. Whereas, amorphous phases usually occurred on grain boundaries, which greatly hinders electron transfer and reduces the catalytic performance. Herein, a NiWSe@NF acicular nanowire electrode was fabricated by a simple hydrothermal strategy, affording outstanding activity and durability, requiring overpotentials of only 103 mV (HER) and 203 mV (OER) under 10 mA cm−2, respectively. Experimental studies and theoretical analysis demonstrate that the excellent catalytic activity is attributed to the interpenetrate structure, which eliminates the formation of amorphous phase and provides a high-speed channel for electron transmission. The crystal interpenetration on grain boundaries adjusts the electronic, promotes the intermediates adsorption and reduce reaction energy barrier. The super-hydrophilic arisen from crystal interpenetration would also reduce the adhesion of generated bubbles and avoid performance attenuation. This work provides a new perspective for the development of high-efficiency composite catalysts. NiWSe@NF electrode with crystal interpenetrating structure eliminates the amorphous phase between interfaces, effectively adjusts the electronic distribution of heterostructure, and achieve ultra-low overpotential bifunctional catalytic activity of HER and OER. [Display omitted] • Neoteric crystal interpenetration featured NiWSe@NF electrode has been prepared. • The NiWSe@NF acicular nanowires electrode shows super-hydrophilic ability. • Crystal interpenetrating structure promotes the intermediates adsorption and reduce reaction energy barrier. • The current density of 10 mA cm−2 can be reached by only 1.53 V of the overall water splitting. • The NiWSe@NF electrode exhibits excellent catalytic stability. [ABSTRACT FROM AUTHOR]

The highly efficient energy conversion of the polymer‐electrolyte‐membrane fuel cell (PEMFC) is extremely limited by the sluggish oxygen reduction reaction (ORR) kinetics and poor electrochemical stability of catalysts. Hitherto, to replace costly Pt‐based catalysts, non‐noble‐metal ORR catalysts are developed, among which transition metal–heteroatoms–carbon (TM–H–C) materials present great potential for industrial applications due to their outstanding catalytic activity and low expense. However, their poor stability during testing in a two‐electrode system and their high complexity have become a big barrier for commercial applications. Thus, herein, to simplify the research, the typical Fe–N–C material with the relatively simple constitution and structure, is selected as a model catalyst for TM–H–C to explore and improve the stability of such a kind of catalysts. Then, different types of active sites (centers) and coordination in Fe–N–C are systematically summarized and discussed, and the possible attenuation mechanism and strategies are analyzed. Finally, some challenges faced by such catalysts and their prospects are proposed to shed some light on the future development trend of TM–H–C materials for advanced ORR catalysis. [ABSTRACT FROM AUTHOR]

Theoretical calculations unveil the charge redistribution over abundant interfaces and the enhanced electronic states of Ru/RuS2 heterostructure. The resulting surface electron‐deficient Ru sites display optimized adsorption behavior toward diverse reaction intermediates, thereby reducing the thermodynamic energy barriers. Experimentally, for the first time the laminar Ru/RuS2 heterostructure is rationally engineered by virtue of the synchronous reduction and sulfurization under eutectic salt system. Impressively, it exhibits extremely high catalytic activity for both OER (201 mV @ 10 mA cm−2) and HER (45 mV @ 10 mA cm−2) in acidic media due to favorable kinetics and excellent specific activity, consequently leading to a terrific performance in acidic overall water splitting devices (1.501 V @ 10 mA cm−2). The in‐depth insight into the internal activity origin of interfacial effect could offer precise guidance for the rational establishment of hybrid interfaces. [ABSTRACT FROM AUTHOR]

• The surface of La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3 perovskite oxides was modified using diluted HNO 3. • Sr cations on A-sites can be selective dissolved by diluted HNO 3. • Surface area and oxygen vacancies were increased with etching time. • The OER performance was enhanced by selective dissolution of the A-site Sr cations. Perovskite oxide is a potential alternative to precious metal oxides like IrO 2 and RuO 2 as electrocatalysts in the oxygen evolution reaction (OER), mostly for its cost-effectiveness and adequate stability. However, the low catalytic activity in the OER limits its practical application. This paper deals with the preparation of perovskite oxides (by the sol-gel method) with enhanced electrocatalytic activity through selective dissolution of A-site cations of La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3 (LSCF) in order to tune the A-site cation deficiency. Additionally, a thorough investigation of the catalysts' OER performance was performed in a 0.1 mol⋅L−1 KOH solution. Based on the results of XRD, SEM, TEM, XPS and ICP-AES, it can be concluded that selective dissolution of Sr cations on A-sites can be achieved using a HNO 3 etching remaining the perovskite structure. The OER catalytic activity of LSCF can be effectively promoted after acid etching for 6 h, which can be attributed to the higher surface area (BET result) and ratio of the high oxidative oxygen species (O2−/O−) and surface oxygen species (OH−/O 2). Moreover, the LSCF catalysts maintains an appropriate electrochemical stability after acid etching. Our work offers a simple but effective way to modify the perovskite surface so as to boost the OER performance. [ABSTRACT FROM AUTHOR]

Single atom catalysts (SAC) have the potential to achieve large-scale production of NH 3 through electrochemical nitrate reduction reaction (NO 3 -RR). Tailoring the coordination structure of the SAC can effectively tune their electronic structure and thus promote their catalytic selectivity and activity. In this work, Fe SAC with unique FeN 2 O 2 coordination was fabricated through direct pyrolysis of metal-organic frameworks that have pre-organized FeN 2 O 4 environment. Fe SAC exhibits both high faradaic efficiency (~92%) and high ammonia yield rate (46 mg h−1 mg cat. −1) in neutral electrolytes. Density functional theory calculations reveal that the O atoms in FeN 2 O 2 can tune the d -band center of Fe and thus adjust the adsorption energies of the NO 3 -RR intermediates. Compared to FeN 4 , FeN 2 O 2 structure has higher conductivity and selectivity to NH 3 and can spontaneously trigger the transformation of *NOH to N * , thus promoting the NO 3 -RR. This work provides a simple method to fabricate O, N-coordinated Fe SAC and may stimulate the flourishing development of asymmetric SAC for electrocatalysis. [Display omitted] ● A novel nut-like MOF was fabricated through the self-assembly of metal ions and ligands. ● Fe single atom catalyst with FeN 2 O 2 configuration can be obtained through the one-step pyrolysis of the as-prepared MOFs. ● Fe single atom catalysts exhibits a high faradaic efficiency of 92%, and a high NH 3 yield rate of 46 mg h−1 mg cat. -1. ● FeN 2 O 2 structure owns the enhanced conductivity and optimized rate-limiting steps compared with FeN 4 structure. [ABSTRACT FROM AUTHOR]