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Alkaline electrochemical water oxidation powered by renewable energies is a promising and environmentally friendly way to produce hydrogen. The industrial water electrolyzers are commonly operated at a high current density, calling for abundant and durable active sites to participate in. The rational design of hierarchically structured electrocatalysts is thus essential to industrial water electrolyzers. Herein, we develop a Fe3+ induced nanosizing strategy for fabricating such a hierarchical FeCo LDH@Co3O4 (LDH: layered double hydroxide) nanostructure array for high-rate water oxidation. Density functional theory (DFT) simulations indicate that the introduction of Fe3+ with a small ion radius and high electrical repulsion in the LDH layer distorted the LDH layer, resulting in a reduced nanosheet size and enabling the formation of a hierarchical structure. Such structure cannot be achieved without the participation of Fe3+ cations. Benefiting from the significantly enhanced electrochemical surface areas and charge/mass transport due to the hierarchical structure together with the boosted intrinsic activity by electronic modulation of Fe3+, such FeCo LDH@Co3O4 electrode can deliver an industrial-level current density of 1,000 mA·cm−2 at a small overpotential of 392 mV for water oxidation. When assembled in a water electrolyzer, it delivers a current density of 100 mA·cm−2 at a low operation voltage of 1.61 V. Powered by solar light, the electrolyzer demonstrates high solar-to-hydrogen efficiency of 18.15% with stable and reproducible photoresponse. These results provide new insights for constructing hierarchical nanostructures for advanced water oxidation and other diverse applications. [ABSTRACT FROM AUTHOR]

Abstract: The development of cost‐effective and applicable strategies for producing efficient oxygen evolution reaction (OER) electrocatalysts is crucial to advance electrochemical water splitting. Herein, a kinetically controlled room‐temperature coprecipitation is developed as a general strategy to produce a variety of sandwich‐type metal hydroxide/graphene composites. Specifically, well‐defined α‐phase nickel cobalt hydroxide nanosheets are vertically assembled on the entire graphene surface (NiCo‐HS@G) to provide plenty of accessible active sites and enable facile gas escaping. The tight contact between NiCo‐HS and graphene promises effective electron transfer and remarkable durability. It is discovered that Ni doping adjusts the nanosheet morphology to augment active sites and effectively modulates the electronic structure of Co center to favor the adsorption of oxygen species. Consequently, NiCo‐HS@G exhibits superior electrocatalytic activity and durability for OER with a very low overpotential of 259 mV at 10 mA cm−2. Furthermore, a practical water electrolyzer demonstrates a small cell voltage of 1.51 V to stably achieve the current density of 10 mA cm−2, and 1.68 V to 50 mA cm−2. Such superior electrocatalytic performance indicates that this facile and manageable strategy with low energy consumption may open up opportunities for the cost‐effective mass production of various metal hydroxides/graphene nanocomposites with desirable morphology and competing performance for diverse applications. [ABSTRACT FROM AUTHOR]

The exploration of new efficient OER electrocatalysts based on nonprecious metals and the understanding of the relationship between activity and structure of electrocatalysts are important to advance electrochemical water oxidation. Herein, we developed an efficient OER electrocatalyst with nickel boride (Ni3B) nanoparticles as cores and nickel(II) borate (Ni-Bi) as shells (Ni-Bi@NB) via a very simple and facile aqueous reaction. This electrocatalyst exhibited a small overpotential of 302 mV at 10 mA cm−2 and Tafel slope of 52 mV dec−1. More interestingly, it was found that the OER activity of Ni-Bi@NB was closely dependent on the crystallinity of the Ni-Bi shells. The partially crystalline Ni-Bi catalyst exhibited much higher activity than the amorphous or crystalline analogues; this higher activity originated from the enhanced intrinsic activity of the catalytic sites. These findings open up opportunities to explore nickel(II) borates as a new class of efficient nonprecious metal OER electrocatalysts, and to improve the electrocatalyst performance by modulating their crystallinity. [ABSTRACT FROM AUTHOR]

The efficiency of CdS-based photocatalysts for H 2 evolution is limited by the ultrafast charge recombination. Here, we demonstrated the one-pot synthesis of a novel MoS 2 /CdS photocatalyst with the structure of partially crystalline MoS 2 nanodots growing on single-crystalline CdS nanorods. This heterostructure not only effectively reduces the bulk and surface charge recombination owing to single-crystalline CdS nanorod matrix and efficient electron transfer, also provides plenty of active sites for hydrogen evolution reaction (HER) and accessible room for prompt hole extraction. The femtosecond transient absorption (TA) analysis reveals the effective electron transfer from CdS to MoS 2 in ~20 ps. As a result, MoS 2 /CdS exhibits extraordinary photocatalytic activity with a H 2 evolution rate of 60.28 mmol/g/h under visible light irradiation, far exceeding all previous HER photocatalysts with MoS 2 as cocatalysts. [ABSTRACT FROM AUTHOR]

Practical electrochemical water splitting requires cost‐effective electrodes capable of steadily working at high output, leading to the challenges for efficient and stable electrodes for the oxygen evolution reaction (OER). Herein, by simply using conductive FeS microsheet arrays vertically pre‐grown on iron foam (FeS/IF) as both substrate and source to in situ form vertically aligned NiFe(OH)x nanosheets arrays, a hierarchical electrode with a nano/micro sheet‐on‐sheet structure (NiFe(OH)x/FeS/IF) can be readily achieved to meet the requirements. Such hierarchical electrode architecture with a superhydrophilic surface also allows for prompt gas release even at high output. As a result, NiFe(OH)x/FeS/IF exhibits superior OER activity with an overpotential of 245 mV at 50 mA cm−2 and can steadily output 1000 mA cm−2 at a low overpotential of 332 mV. The water‐alkali electrolyzer using NiFe(OH)x/FeS/IF as the anode can deliver 10 mA cm−2 at 1.50 V and steadily operate at 300 mA cm−2 with a small cell voltage for 70 h. Furthermore, a solar‐driven electrolyzer using the developed electrode demonstrates an exceptionally high solar‐to‐hydrogen efficiency of 18.6%. Such performance together with low‐cost Fe‐based materials and facile mass production suggest the present strategy may open up opportunities for rationally designing hierarchical electrocatalysts for practical water splitting or diverse applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Water-dissociation-active FeOOH was coupled with MoS 2 on Ni3S 2 nanowire arrays to achieve a core-shell Ni3S 2 @MoS 2 /FeOOH heterostructure. • The as-prepared Ni3S 2 @MoS 2 /FeOOH exhibited a small overpotential of 95 mV for HER and 234 mV for OER at 10 mA cm −2 . • The enhanced activity for both OER and HER was ascribed to the coupling effect and electronic modulation between FeOOH and MoS 2. • The present strategy enlightens the development of new electrocatalysts by coupling OER-active component with highly-active HER catalysts. Abstract MoS 2 has emerged as an attractive electrocatalyst for hydrogen evolution reaction (HER) although its performance still needs to be further enhanced, especially in alkaline solution due to inferior ability for water dissociation. Herein, we discover that coupling water-dissociation-active FeOOH with MoS 2 grown on Ni 3 S 2 nanowire arrays to achieve a core-shell Ni 3 S 2 @MoS 2 /FeOOH heterostructure can not only significantly accelerate the HER of MoS 2 , but also appreciably promote the OER activity of the catalyst. Systematic investigations on Ni 3 S 2 @MoS 2 /FeOOH and a series of delicately designed control catalysts reveal that such synergistically enhanced electrocatalytic performance for both OER and HER should be ascribed to the coupling effect and electronic modulation between FeOOH and MoS 2. As a result, the prepared Ni 3 S 2 @MoS 2 /FeOOH exhibits small overpotentials of 95 mV for HER and 234 mV for OER at 10 mA cm−2. The alkaline electrolyzer using it as both anode and cathode only need a cell voltage of 1.57 V to output a stable current density of 10 mA cm−2, enabling it as an efficient bifunctional electrocatalyst for alkaline overall water splitting. The present strategy opens up opportunities to develop new efficient electrocatalysts for diverse applications by coupling OER-active electron-modulating component with highly-active HER electrocatalyst or vice versa. [ABSTRACT FROM AUTHOR]