Bifunctionality behavior of phase controlled nickel selenides in alkaline water electrolysis application

Insight into selenium vacancies enhanced CoSe2/MoSe2 heterojunction nanosheets for hydrazine-assisted electrocatalytic water splitting

The integration of interface engineering and vacancy engineering was a feasible way to develop highly efficient electrocatalysts toward water electrolysis. Herein, we designed CoSe2/MoSe2 heterojunction nanosheets with abundant Se vacancies (VSe-CoSe2/MoSe2) for electrocatalytic water splitting. In the VSe-CoSe2/MoSe2 electrocatalyst, the electrons more easily transferred from CoSe2 to MoSe2, and interface engineering not only modulated the electronic structure, but also supplied more heterointerfaces and catalytic sites. After chemical etching, partial Se atoms were eliminated, which further activated the inert plane of the VSe-CoSe2/MoSe2 electrocatalyst and induced electron redistribution. The removal of surface Se atoms was also beneficial to expose inner reactive sites, which promoted adsorption toward reaction intermediates. Density functional theory calculations revealed that interface engineering and vacancy engineering collaboratively optimized the adsorption energy of the VSe-CoSe2/MoSe2 electrocatalyst toward the intermediate H* during the hydrogen evolution reaction process, leading to better electrocatalytic activity. The density of state diagram manifested the refined electronic structure of the VSe-CoSe2/MoSe2 electrocatalyst, and it exhibited a higher electronic state near the Fermi level, which indicated superior electronic conductivity, facilitating electron transport during the catalytic process. In alkaline media, the VSe-CoSe2/MoSe2 electrocatalyst delivered low overpotentials of merely 74 and 242 mV to obtain 10 mA cm-2 toward hydrogen evolution reaction and oxygen evolution reaction. This work illustrated the feasibility of combining two or more strategies to develop high-performance catalysts for water electrolysis.

Regulable in-situ autoredox for anchoring synergistic Ni/NiO nanoparticles on reduced graphene oxide with boosted alkaline electrocatalytic oxygen evolution

To develop ideal alternatives to noble metal catalysts, transition metal catalysts supported on graphene have been receiving extensive attention in the field of electrochemical energy. In this work, using graphene oxide (GO) and nickel formate as precursors, Ni/NiO synergistic nanoparticles with regulable composition are anchored on reduced graphene oxide (RGO) to prepare Ni/NiO/RGO composite electrocatalysts through in-situ autoredox. Thanks to the synergistic effect of Ni³⁺ active sites and Ni electron donors, the as-prepared Ni/NiO/RGO catalysts exhibit efficient electrocatalytic oxygen evolution performance in 1.0 M KOH electrolyte. The optimal sample has an overpotential of only 275 mV at a current density of 10 mA cm^-2 and a small Tafel slope of 90 mV dec^-1, which are very comparable to those of commercial RuO₂ catalyst. Additionally, the catalytic capacity and structure remain stable after 2000 cyclic voltammetry cycles. For the electrolytic cell assembled with the best-performing sample as anode and commercial Pt/C as cathode, the current density can reach 10 mA cm^-2 at a low potential of 1.57 V and remains stable after 30 h of continuous work. It would be expected that the as-developed Ni/NiO/RGO catalyst with high activity should have broad application prospects.

Electronic modulation and proton transfer by iron and borate co-doping for synergistically triggering the oxygen evolution reaction on a hollow NiO bipyramidal prism

Designing an Earth-abundant and inexpensive electrocatalyst to drive the oxygen evolution reaction (OER) for high-purity hydrogen production is of great importance. Herein, the cation (iron) and anion (borate) co-doping strategy was proposed to effectively trigger the OER performance on a low-cost NiO material. The optimal hollow Fe/B_i-NiO bipyramidal prism shows superior OER performance, and displays a low overpotential (261 mV) at 10 mA cm^-2, accompanied by a low Tafel slope (46 mV dec^-1), excellent intrinsic activity and robust stability. The overall alkaline water splitting using Fe/B_i-NiO/NF as an anode affords low cell voltages of 1.50 and 1.63 V at 10 and 100 mA cm^-2, and operates steadily at a high current density of 100 mA cm^-2 for 55 h without decay. The excellent electrocatalytic activity could be ascribed to the hollow structure to shorten the mass transfer pathway, the electronic modulation by Fe doping, the increased accessible electroactive sites created by oxygen vacancies through borate doping, and the formation of BO₃^3--OH^- to accelerate the deprotonation of OH_ads.