Heterostructure of NiCo2O4@Ni-CeO2 for High Current Density Water Splitting

Abstract

This study investigates the synthesis and characterization of NiCo₂O₄@Ni–CeO₂ heterostructures for enhanced electrolysis applications. Seven different electrodeposition approaches were systematically evaluated, including stepwise and co-electrodeposition methods, to understand the relationship between synthesis methodology and electrochemical performance. The research addresses the critical need for cost-effective, earth-abundant electrocatalysts to replace expensive noble metals in water splitting technology for green hydrogen production. Our findings demonstrate that synthesis approach dramatically influences catalytic performance. Sample S7, synthesized via co-electrodeposition, achieved exceptional oxygen evolution reaction (OER) performance with an overpotential of 297 mV at 20 mA cm⁻², significantly outperforming individual components and demonstrating competitive performance against literature benchmarks. However, this sample showed poor hydrogen evolution reaction (HER) activity (404 mV at -10 mA cm⁻²), highlighting the inherent challenges in bifunctional catalyst design. Conversely, samples S2 and S4 exhibited excellent HER performance (136 mV each) but relatively poor OER activity. Comprehensive characterization using scanning electron microscopy, Raman spectroscopy, and electrochemical impedance spectroscopy revealed that co-electrodeposition creates uniform heterostructures with enhanced interfacial contact and optimal charge transfer properties (Rct = 1.5 Ω). Surface wettability analysis confirmed superhydrophilic properties (0° contact angle) for the co-electrodeposited sample, facilitating improved electrolyte-catalyst interaction. Light- enhanced measurements demonstrated photocatalytic enhancement across all samples, indicating potential for solar-driven applications. Overall water splitting analysis revealed that sample S4 achieved the lowest total cell voltage (1.727 V), emphasizing that balanced bifunctional performance is more critical than excellence in single half-reactions. The results highlight fundamental trade-offs in heterostructured catalyst design, where optimization for one reaction often compromises performance in the other. This work provides valuable insights into structure-performance relationships and demonstrates the potential of electrodeposited NiCo₂O₄@Ni–CeO₂ heterostructures for practical water splitting applications.