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[Display omitted] • Heterojunction of FeNi LDH/FeNi 2 S 4 was firstly constructed via one-step process. • Electrochemical bifunctional applications of the heterojunctions are investigated. • The heterojunctions exhibited excellent electrochemical catalytic ability for OER. • An improved specific capacitance was obtained with heterojunctions electrode. Construction of heterogeneous phases offers a promising strategy to tailor the physiochemical properties of electrode materials to improve their electrochemical performance toward energy conversion and capacitive storage. Herein, the hetero-phase combination of hexagonal FeNi layered double-hydroxide (FeNi-LDH) and spinel phase FeNi 2 S 4 microsphere assembled with nanosheets is synthesized via one-step solvothermal process. Owing to improved components, unique micro-structures and the construction of heterogeneous engineering between FeNi LDH and FeNi 2 S 4 with abundant active interface, FeNi LDH/FeNi 2 S 4 heterojunctions exhibit an excellent electrochemical performance for oxygen evolution reaction (OER) and hybrid capacitive storage. The heterojunctions show low overpotential of 259 mV at 10 mA cm−2, small Tafel slope of 75 mV dec−1, excellent cyclic stability in OER, as well as an improved specific capacity of 472.5C g−1 at 1 A g−1 in hybrid capacitors. The preparation and dual-function applications of FeNi LDH/FeNi 2 S 4 heterojunctions provide a new idea as the advanced electrode materials for electrocatalytic OER and hybrid capacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spinel offers great opportunities in electrocatalytic water oxidation. • Advances in engineering spinel-based catalysts for water oxidation are manifested. • Some advanced strategies for engineering spinels are highlighted. • Challenges and improvement directions in this field are also discussed. Fabricating advanced oxygen evolution reaction (OER) catalysts is of vital significance for the effectiveness of water splitting. Endowed with high catalytic performance toward OER, spinel-type materials are universally agreed to be one of most promising alternatives to the currently used noble metal-based electrocatalysts. Nonetheless, a major issue that limits the practical applications of spinel-type materials as OER catalysts is the high OER overpotential. Aiming to enable spinel-type materials to serve as practical OER electrocatalysts, intensive endeavors have been dedicated to the optimization of electrochemical properties by modifying their structures and compositions. Given that, summarizing the recent progress of spinel electrocatalysts with modified electronic configurations and their applications in OER is highly desirable. This review starts by introducing the OER mechanisms which involves with the conventional adsorbate evolution mechanism (AEM) and lattice oxygen mechanism (LOM). In addition, the OER pathways with spinel electrocatalysts and some important descriptors have also been summarized. Afterwards, many advanced strategies that have been demonstrated to be effective for optimizing the electrochemical properties of spinel electrocatalysts are predominately discussed. Finally, the perspective insights in advancing deep understanding and fabricating excellent spinel-type electrocatalysts are also manifested. [ABSTRACT FROM AUTHOR]

Ru doping and sulfur vacancy engineering synergistically modify the electronic structure of FeNi 2 S 4 to boost electrocatalytic oxygen evolution reaction. [Display omitted] • A facile ion doping and vacancy engineering strategy has been proposed for modifying the electronic structure. • Ru doping and S vacancy concurrently facilitate the surface reconstruction of FeNi 2 S 4. • The in situ formed Ni3+-rich oxyhydroxides are highly active toward OER. • The Ru-FeNi 2 S 4-x catalyst can exhibit outstanding electrocatalytic OER performance. Electronic structure engineering lies at the heart of the catalyst design, however, utilizing one strategy to modify the electronic structure is still challenging to achieve optimal electronic states. Herein, an advanced approach that incorporating both Ru dopants and sulfur vacancies into thiospinel-type FeNi 2 S 4 to synergistically modulate the electronic configuration, is proposed. Deep characterizations and theoretical study reveal that the in-situ formed Ni3+ species are real active centers. Ru doping and sulfur vacancies synergistically tune the electronic states of Ni2+ sites to a near-optimal value, leading to the formation of abundant oxygen evolution reaction (OER)-active Ni3+ species via electrochemical reconstruction. Consequently, the optimized Ru-FeNi 2 S 4 catalyst can exhibit superb electrocatalytic performance towards OER, delivering the overpotentials of 253 mV and 340.8 mV at 10 mA·cm−2 in alkaline water and seawater, respectively. The proper combination of vacancy and heteroatom doping in this work may unlock the catalytic power of conventional catalysts toward electrochemical reactions. [ABSTRACT FROM AUTHOR]