Diatom derived hollow 3D Frame as a synergetic support for millerite nanoparticles: A unique hydrogen evolution electrocatalyst and its mechanistic insights

The embedding of metal nanoparticles (NPs) on/into porous supports, including alumina, zeolites, and porous carbon materials, has recently been widely studied to develop advanced catalysts for various energy-related applications. Unlike conventional support materials, diatoms (i.e., Bacillariophyceae), naturally available aluminosilicate materials with a hollow, three-dimensional (3D) porous, durable structure, provide unique opportunities as a support material of metal nanoparticle catalysts for energy-related catalytic applications. Here, we developed an environmentally benign diatom/NiS (Millerite (NiS)) hetero-catalyst for electrocatalytic application. The prepared hetero-composite material was characterized using various analytical methods to understand the structural features and the chemical nature. The diatom/NiS nanocatalyst demonstrated remarkable hydrogen evolution reaction (HER) activity, achieving a low overpotential (53.6 mV) and Tafel slope (55.1 mV dec⁻¹) in sulfuric acid (0.50 M) at −10 mA cm⁻² current density comparable to the commercial noble metal catalyst (Pt/C), which was significantly enhanced than pure NiS. The product (H₂) analysis proved the quantitative Faradaic efficiency (99.74 %). The results of the density functional theory (DFT) calculations allow a fundamental understanding of the unique catalytic activity of the material. The DFT calculation results revealed that embedding NiS nanoparticles in diatoms generated effective active sites, resulting in the low ΔG_H* (−0.05 eV) for the diatom/NiS heterostructure. Further experiments proved that the heterostructure showed a catalytic activity in oxygen evolution reaction (OER) in a basic medium. This work presents the unique cooperative catalytic behavior of diatom-supported NiS nanoparticle heterostructure, and the proposed strategy can represent the development of a noble eco-friendly electrocatalyst for energy conversion and harvesting.