Insights into Hydrogen Spillover via Heterointerface Engineering and Spin State Density Modulation in CoO-Co<sub>3</sub>O<sub>4</sub>/rGO@NiP Hybrids for Alkaline Hydrogen Evolution
Muraleedharan Sheela Meera, Sarika Sasidharan, Sneha George, S.M.A. Shibli
Abstract
Heterointerface and defect engineering, coupled with electronic structure modulation, are powerful strategies for designing advanced electrocatalysts for sustainable energy. Herein, we integrate CoO-Co 3 O 4 /rGO onto a NiP matrix, leveraging their synergistic properties to enhance alkaline HER performance. The presence of heterointerfaces, defects, oxygen vacancies, and synergistic interactions within CoO-Co 3 O 4 /rGO@NiP modulates the overall electronic spin state density and enhances the net electronic conductivity among the electron-donating channels. The present in situ synthesis strategy reduces GO to rGO and deposits CoO-Co 3 O 4 on rGO layers, preventing rGO restacking and maximizing the exposure of the active sites in mixed-valence metal oxides. During the multistep HER process, the electron-enriched Co 2+ at CoO sites facilitates H + adsorption, and the high-valence Co 3+ in Co 3 O 4 promotes H 2 O activation and dissociation. The HER activity of the hybrid coating has a low overpotential (η 10 = 106.2 mV), low Tafel slope (107.9 mV dec –1 ), diminished R CT value, and long-term durability in 1.0 M NaOH electrolyte. This stems from the oxygen vacancies as well as Jahn–Teller-active e g orbitals with high spin state density at the heterointerface, enabling the fast charge transfer kinetics of HER on CoO-Co 3 O 4 /rGO@NiP.