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Designing effective and low-cost bifunctional electrocatalysts for the alkaline hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential to achieve green development of the hydrogen economy. Herein, we have developed Mo-doped Ni3S2 nanosheet array catalysts with excellent electrochemical properties. Only 85 mV (HER) and 230 mV (OER) overpotentials are required under alkaline conditions at 10 mA cm–2 and remain undegraded for 100 h. In addition, it only required 1.52 V at 10 mA cm–2 in an alkaline electrolyzer, and it remained unchanged for more than 100 h in stability tests, outperforming most reported electrocatalysts. Experiments and density functional theory (DFT) calculations confirmed that the doping of Mo could expose more active sites of Ni3S2 and optimize the adsorption free energy of the intermediate, which in turn improves its intrinsic activity. This work reveals the key role of Mo in Ni3S2 electrocatalytic performance enhancement at the atomic scale. [ABSTRACT FROM AUTHOR]

Boosting the hydrogen evolution reaction (HER) process with highly efficient non-noble metal catalysts is crucial for hydrogen-powered fuel cells. Pyrite-type NiSe2 is one of the most promising HER catalysts due to its inexpensive cost and good conductivity, although its intrinsic activity is moderate. Using a plasma etching method on a carbon cloth substrate material, we created a large number of selenium vacancies on NiSe2 nanosheets (NiSe2-VSe/CC). With a low overpotential of 91 mV and a Tafel slope of 91 mV dec–1 at 10 mA cm–2, as well as a durability of 20 h at high current (100 mA cm–2), the NiSe2-VSe/CC demonstrates superior HER performance for its catalytic activity and long-term stability. Cross-validated by measurement analyses and density functional theory calculations, the introduction of vacancies reduces the resistivity of NiSe2 and optimizes its hydrogen adsorption energy (GH*) and water adsorption energy (GH2O*). Based on defect engineering, this study proposes an approach to designing improved electrocatalysts for alkaline HER. [ABSTRACT FROM AUTHOR]

Abstract Developing efficient, non-noble electrocatalysts toward hydrogen evolution reaction (HER) in alkaline electrolytes is of important significance for future energy supplement but still a challenge. Recently, pyrite-type NiSe 2 nanomaterial has been considered as an idea HER electrocatalyst due to its high conductivity, strong corrosion resistance and low cost. However, the HER performance of NiSe 2 in alkaline electrolytes is still unsatisfactory, which is possibly limited to the activate water dissociation in alkaline media. Herein, a novel hybrid electrocatalyst of Ni(OH) 2 /NiSe 2 nanosheet arrays on carbon cloth (Ni(OH) 2 /NiSe 2 /CC) is fabricated, exhibiting excellent HER catalytic activity with a low overpotential of 82 mV to drive a current density of 10 mAcm−2 as well as maintaining a long-term durability for 12 h in 1.0 M KOH, which is 77 mV less than that of NiSe 2 /CC and superior to most recently reported non-noble HER electrocatalysts. In addition, the Tafel slope of Ni(OH) 2 /NiSe 2 /CC (60 mV dec −1) is also much smaller than that of NiSe 2 /CC (112 mV dec −1), suggesting a promotion kinetics of HER process for Ni(OH) 2 /NiSe 2 /CC. Our further experimental results show that the significantly improved activity of Ni(OH) 2 /NiSe 2 /CC electrode should ascribe to its enlarged active surface, good conductivity and interfacial synergy between Ni(OH) 2 and NiSe 2. The synergetic strategy may provide an efficient way to promote the HER activity of other non-noble transition metal selenides in alkaline electrolyte. Highlights • The Ni(OH) 2 /NiSe 2 nanosheet arrays was fabricated for the first time. • Ni(OH) 2 /NiSe 2 exhibits excellent HER activity in alkaline media. • The hybrid catalyst also displays excellent long-term durability. [ABSTRACT FROM AUTHOR]

• A novel self-supported Ni 2 P-NiSe 2 heterostructure catalyst was fabricated. • Ni 2 P-NiSe 2 catalyst exhibits excellent HER activity (66 mV@10 mA cm−2) in 1 M KOH. • Ni 2 P-NiSe 2 shows excellent durability with barely degradation for 12 h. • XPS and DFT results confirm the strongly electronic interaction in the interface. • The optimized hydrogen/water adsorption energy are responsible for enhanced HER. Developing earth-abundant transition-metal phosphides electrocatalysts with high activity and good durability toward alkaline hydrogen evolution reaction (HER) is crucial for sustainable hydrogen energy economy. However, their intrinsic activity is limited by the inadequate hydrogen adsorption energy. Herein, we reported a novel self-supported heterostructure catalyst in the form of Ni 2 P-NiSe 2 , which is obtained by phosphorization of NiSe 2 nanosheet arrays grown on the carbon cloth. The heterostructure catalyst exhibits excellent HER performance in 1 M KOH, only requiring an overpotential of 66 mV at a current density of 10 mA cm−2 with a Tafel slope of 72.6 mV dec-1 and showing excellent long-term durability. The experimental and theoretical calculation results demonstrate the strongly electronic interaction between Ni 2 P and NiSe 2 , resulting in the optimized Gibbs free energy of hydrogen and water adsorption. This work concerning the regulation of electronic structure through interface engineering may offer a deep insight to explore superior catalysts. [ABSTRACT FROM AUTHOR]