Ligand-induced room-temperature synthesis of NiCoSe nanostructures: a highly efficient electrocatalyst for hydrazine-assisted hydrogen production

Abstract

Transition metal selenides are considered to be promising electrode materials to catalyze various electrocatalytic reactions. The synthesis of these metal selenides involves harsh synthetic conditions and multistep routes. Herein, a room-temperature ligand-assisted strategy has been developed to synthesize NiSe, CoSe, and NiCoSe in a pure phase. This study delves into the significant impact of ligands on nanoparticle synthesis, with a particular focus on their pivotal role in finely adjusting the crystalline phase of the resulting nanomaterials. We have focused on identifying the specific ligands that can effectively manipulate nucleation and growth processes for the synthesis of specific crystal structures of MSe (M = Ni, Co). The role of functional groups in ligands was probed, and it was found that the carboxylic acid groups play a key role in facilitating the synthesis of pure-phase NiSe, CoSe, and NiCoSe. Through a detailed examination of the existing literature and theoretical calculations, we have investigated the mechanism and role of carboxylate ligands in MSe (M = Ni, Co) formation. Computational investigations suggest that the formation of a metastable metal–carboxylate intermediate complex optimizes the reaction condition, makes it more favorable for reorientation, and allows selenium to approach the nickel center. Furthermore, the synthesis of NiCoSe aims to enhance the electrocatalytic performance of NiSe and CoSe, as the bimetallic (NiCoSe) material exhibits superior electrochemical properties compared to its monometallic counterparts. The electrocatalytic activities of the synthesized transition metal selenides were evaluated for hydrazine-assisted water splitting. Bimetallic NiCoSe displays superior electrocatalytic performance toward hydrazine oxidation and hydrogen evolution reactions compared to the monometallic phases of NiSe and CoSe. The bimetallic component requires a potential of 0.20 V vs. RHE and an overpotential of 0.20 V to attain 10 mA cm⁻² for the HzOR and HER, respectively. Moreover, NiCoSe displays excellent activity as a bifunctional catalyst, and it requires a very low cell voltage of 0.45 V to attain a current density of 10 mA cm⁻² for H₂ production. The free energy profile of the stepwise HzOR has been investigated in detail. The computational results reveal the enhanced feasibility of the HzOR on NiCoSe (1 : 1) compared to NiSe. Therefore, briefly, this work offers an innovative synthesis protocol for the ligand-induced room-temperature synthesis of transition metal selenide nanostructures and their application for hydrazine-assisted hydrogen production.