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Rational design of highly conductive and hydrophilic electrocatalysts are extremely important to promote their oxygen evolution reaction (OER). In this work, a homogeneously dispersed carbon-based cobalt/iron catalyst (Co/Fe–C) with abundant oxygen vacancies and favorable hydrophilicity is fabricated via a facile metal-polyphenol complexes strategy. The tannic acid (TA) and fulvic acid (FA) derived 0.3 Co/Fe–C catalysts show greatly similar morphologies, as well as the performance optimization process of electrocatalytic OER. Specifically, the TA-derived 0.3 Co/Fe–C catalyst exhibits an overpotential of 284 mV at 10 mA cm−2 for OER in alkaline electrolyte. Combined a series of characterization techniques suggest that abundant oxygen vacancies and favorable surface hydrophilicity can improve electronic conductivity of the catalyst and accelerate reactant adsorption and charge transfer rate on the catalyst surface, thus promoting OER activity of the catalysts. This study might provide a new perspective to construct advanced electrocatalysts with oxygen vacancies and hydrophilic surface for electrocatalytic applications. [Display omitted] • A facile metal-polyphenols complexes strategy for synthesizing Co/Fe–C catalysts. • Oxygen vacancies and hydrophilicity result in highly activity of Co/Fe–C catalyst. • 0.3 TA−Co/Fe–C catalyst revealed excellent OER activity of 284 mV at 10 mA cm−2. • This work realizes low-temperature synthesis of conductive and hydrophilic catalysts. [ABSTRACT FROM AUTHOR]

Ni3S2 has been validated as an effective electrocatalyst for the oxygen evolution reaction, attributable to its suitable electronic configuration. However, pure Ni3S2 towards the hydrogen evolution reaction (HER) exhibits relatively low catalytic activity. Herein, a one-step annealing strategy is demonstrated for the synthesis of Ni3S2 nanowires on nickel foam (NF) through N doping towards vigorous HER performance both in acid and alkaline solution. The 1D N-Ni3S2 nanowires, integrated onto a 3D NF electrode, show a high catalytic current density of 10 mA cm−2 at a low overpotential of 196 mV and a small Tafel slope of 63 mV dec−1 in an acid electrolyte. In an alkaline medium, the N-Ni3S2 NWs exhibit a low overpotential of 105 mV at the current density of 10 mA cm−2, which is lower than other reported Ni3S2-based HER catalysts. The superior HER catalytic performance is attributed to its unique structural features, both the morphology and electronic structure. Our work provides profound guidance for the design and optimization of electrocatalysts for an efficient HER. [ABSTRACT FROM AUTHOR]

[Display omitted] • A unit cell activation strategy to prepare MoO x in MoNi alloy for promoting HER activity. • MoO 4 tetrahedrons as the unit cell of NiMoO 4 can be transformed into MoO x under HER. • MoO x instead of self-dissolution and restructure of Mo in MoNi alloy for stabilizing HER. • MoO x /MoNi performs an excellent HER activity even surpasses commercial Pt/C. • MoO x has the capacity to weaken bonding energy barrier of hydrogen desorption on Ni. MoNi alloys as excellent alkaline hydrogen evolution reaction (HER) electrocatalysts benefit from activated Mo-based polymerides for optimizing hydrogen desorption of Ni site. Mo-based polymerides are transformed from adsorbed MoO 4 2−, which is formed by dissolved Mo. However, the dissolution behavior of Mo is uncontrollable and adsorbed MoO 4 2− is limited, resulting in reduced activity of the MoNi alloys. Herein, we reported a unit cell activation strategy to prepare activated MoO x species in MoNi (MoO x /MoNi) alloy for boosting performance in alkaline HER. Characterization by Raman spectroscopy shows that activated MoO x species in MoNi alloy are mainly derived from MoO 4 tetrahedrons of the β-NiMoO 4 under HER, which have strong correlation with the HER performance of the catalyst. The obtained MoO x /MoNi performs a brilliant HER activity with a low overpotential and Tafel slope of 35 mV@10 mA cm−2 and 58 mV dec−1, respectively, even surpassing commercial Pt/C. As revealed by a series of characterization techniques and theoretical methods, the brilliant HER activity can be ascribed to both the capacity of MoO x on adjusting the hydrogen desorption of Ni site and the intrinsic property of the MoNi alloy. Significantly, activating MoO 4 tetrahedrons to MoO x species is an efficient way to replace the self-dissolution and restructure of Mo in MoNi alloy, which could effectively minimize the adverse effect of dissolved Mo on the catalytic activity of MoNi alloy. This work demonstrates the activation process of MoO 4 tetrahedrons to MoO x species, providing a new insight into designing and fabricating high-performance HER catalysts by unit cell activation instead of self-dissolution and restructure. [ABSTRACT FROM AUTHOR]

The synergistic achievement of low-cost earth-abundant electrocatalysts and high efficiency to meet renewable energy need is highly desirable yet challenging. Here, we developed a simple Ni foam self -templating route for V-doped Ni 3 S 2 nanosheet arrays through in situ formation of metal-organic frameworks (MOFs) combined with subsequent conversion. The as-prepared MOF-V-Ni 3 S 2 /NF catalyst delivers outstanding electrocatalytic performance in the alkaline solution, which requires low overpotentials of 118.1 mV @10 mA cm−2 and 268 mV @10 mA cm−2 for hydrogen evolution reaction and oxygen evolution reaction, respectively. The V-doping and MOF-derived 3D hieratical nanostructure play a vital role in the catalytic process, which provides efficient active sites and large surface areas. Furthermore, an alkaline electrolyzer was assembled with two pieces of MOF-V-Ni 3 S 2 /NF, which achieves efficient water splitting at 1.58 V @10 mA cm−2. This strategy opens up new channels to synthesize MOF-based bifunctional electrocatalysts toward overall water spitting. Image 1 • Combining metal doping with nanostructuring for efficient water splitting in alkali. • Ni-MOF-derived V-doped Ni 3 S 2 hieratical nanostructure was successful synthesized. • Providing optimized η 10 of 118 mV and 268 mV for HER and OER, respectively. [ABSTRACT FROM AUTHOR]

In this paper, a facile hydrothermal synthetic strategy was developed for MoS 2 nanoflowers with enlarged interlayer spacing on the carbon cloth (CC) as a high efficiency cathode electrode for hydrogen evolution reaction (HER) under wide pH condition. It was observed that the loading amount of MoS 2 has a major impact on the HER performance, where the optimized MoS 2 /CC exhibited a low onset potential of 94 mV and a small Tafel slope of 50 mV dec −1 in strong acid solution (pH = 0). The improved HER performance can be contributed to the enlarged interlayer spacing, abundant defects and more exposed active sites in the small size MoS 2 nanosheets as revealed by XRD and HRTEM. Meanwhile, it also exhibited relatively good performance for HER under basic and neutral conditions with the overpotentials of 188 (pH = 14) and 230 (pH = 7) mV to achieve current density of 10 mA cm −2 and the Tafel slopes of 52 and 84 mV dec −1 , respectively. [ABSTRACT FROM AUTHOR]