Combined effect of nitrogen-doped carbon and NiCo₂O₄ for electrochemical water splitting

Electrocatalytic water splitting for green hydrogen production necessitates effective electrocatalysts. Currently, commercial catalysts are primarily platinum-based. Therefore, finding catalysts with comparable catalytic activity but lower cost is essential. This paper describes spinel-structured catalysts containing nickel cobaltite NiCo₂O₄, graphene, and additionally doped with heteroatoms. The structure and elemental composition of the obtained materials were analyzed by research methods such as TEM, SEM-EDX, XRD, XPS, and Raman spectroscopy. The electrochemical measurements showed that hybrid materials containing nickel cobaltite NiCo₂O₄ doped with graphene are highly active catalysts in the hydrogen evolution reaction (Tafel slopes = 91 mV dec^-1, overpotential = 468 mV and onset potential = -339 mV), while in the oxygen evolution reaction (Tafel slopes = 51 mV dec^-1, overpotential = 1752 mV and onset potential = 370 mV), bare NiCo₂O₄ without the addition of carbon has a worse activity (for HER: Tafel slopes = 120 mV dec^-1, overpotential - does not achieve and onset potential = -404 mV, for OER: Tafel slopes = 54 mV dec^-1, overpotential = 1796 mV and onset potential = 410 mV). In terms of stability, comparable results were obtained for each synthesized compound for both the HER and OER reactions.