Developing highly effective and stable non-noble metal-based bifunctional catalyst working at high current density is an urgent issue for water electrolysis (WE). Herein, we prepare the N-doped graphene-decorated NiCo alloy coupled with mesoporous NiCoMoO nano-sheet grown on 3D nickel foam (NiCo@C-NiCoMoO/NF) for water splitting. NiCo@C-NiCoMoO/NF exhibits outstanding activity with low overpotentials for hydrogen and oxygen evolution reaction (HER: 39/266 mV; OER: 260/390 mV) at ± 10 and ± 1000 mA cm⁻². More importantly, in 6.0 M KOH solution at 60 °C for WE, it only requires 1.90 V to reach 1000 mA cm⁻² and shows excellent stability for 43 h, exhibiting the potential for actual application. The good performance can be assigned to N-doped graphene-decorated NiCo alloy and mesoporous NiCoMoO nano-sheet, which not only increase the intrinsic activity and expose abundant catalytic activity sites, but also enhance its chemical and mechanical stability. This work thus could provide a promising material for industrial hydrogen production.

Constructing heterojunction is an effective strategy to develop high-performance non-precious-metal-based catalysts for electrochemical water splitting (WS). Herein, we design and prepare an N-doped-carbon-encapsulated Ni/MoO₂ nano-needle with three-phase heterojunction (Ni/MoO₂@CN) for accelerating the WS under industrial alkaline condition. Density functional theory calculations reveal that the electrons are redistributed at the three-phase heterojunction interface, which optimizes the adsorption energy of H- and O-containing intermediates to obtain the best ΔG_H* for hydrogen evolution reaction (HER) and decrease the ΔG value of rate-determining step for oxygen evolution reaction (OER), thus enhancing the HER/OER catalytic activity. Electrochemical results confirm that Ni/MoO₂@CN exhibits good activity for HER (ƞ_-10 = 33 mV, ƞ_-1000 = 267 mV) and OER (ƞ₁₀ = 250 mV, ƞ₁₀₀₀ = 420 mV). It shows a low potential of 1.86 V at 1000 mA cm⁻² for WS in 6.0 M KOH solution at 60 °C and can steadily operate for 330 h. This good HER/OER performance can be attributed to the three-phase heterojunction with high intrinsic activity and the self-supporting nano-needle with more active sites, faster mass diffusion, and bubbles release. This work provides a unique idea for designing high efficiency catalytic materials for WS.

Water electrolysis is a promising approach for large-scale and sustainable hydrogen production; however, its kinetics is slow and requires precious metal electrocatalysts to efficiently operate. Therefore, great efforts are being undertaken to design and prepare low-cost and highly efficient electrocatalysts to boost the hydrogen evolution reaction (HER). This is because traditional transition-metal electrocatalysts and corresponding hybrids with nonmetal atoms rely mainly on the interaction of metal–H bonds for the HER, which inevitably suffers from corrosion in extreme acidic and alkaline solutions. And as a result of all this effort, novel nanostructured electrocatalysts, such as carbon-encapsulated precious metals and non-precious metals including single metals or their alloys, transition-metal carbides, phosphides, oxides, sulfides, and selenides have all been recently reported to exhibit good catalytic activities and stabilities for hydrogen evolution. Here, the catalytic activity is thought to originate from the electron penetration effect of the inner metals to the surface carbon, which can alter the Gibbs free energy of hydrogen adsorption on the surface of materials. In this review, recent progresses of carbon-encapsulated materials for the HER are summarized, with a focus on the unique effects of carbon shells. In addition, perspectives on the future development of carbon-coated electrocatalysts for the HER are provided.