Trifunctional noble-metal-free multi-site electrocatalysts based on NiMn-LDH/CuCo2S4/rGO for energy-saving hydrogen generation via the UOR/HER/OER

Abstract

The need to produce eco-friendly and renewable energy sources has encouraged researchers to develop efficient non-noble electrocatalysts for urea-splitting systems. The current study seeks to create ternary composites – NiMn layer double hydroxide (NiMn-LDH) and CuCo₂S₄ nanorods on reduced graphene oxide (rGO) as catalysts for the urea oxidation reaction (UOR). The highest electrocatalytic performance towards the UOR was observed for the NiMn-LDH/CuCo₂S₄/rGO@NF electrode, due to its unique structural profile, quick charge transfer, and greater exposure of active sites. Only a low potential of 1.27 V was required to achieve a 10 mA cm⁻² current density for this composite, which exhibited a low Tafel slope of 136 mV dec⁻¹. In addition, the overpotential of 220 mV has been reported for the oxygen evolution reaction (OER) at 10 mA cm⁻² current density. Besides these features, the ternary NiMn-LDH/CuCo₂S₄/rGO@NF is remarkably durable and stable in OER and UOR processes over long time periods. The NiMn-LDH/CuCo₂S₄/rGO@NF electrocatalyst also showed the lowest activation energy of 7.78 kJ mol⁻¹ and 5.08 kJ mol⁻¹ and a TOF of 0.017 s⁻¹ and 0.124 s⁻¹ for the OER and UOR, respectively. The presented strategy allows for the improvement of the composites' electron configuration while simultaneously providing several phase interfaces by incorporating active sites of binary NiMn-LDH/CuCo₂S₄ anchored on rGO, leading to subsequent enhancement in inherent conductivity and electron transport. This study introduces a facile strategy for fabricating trifunctional electrocatalysts, potentially useful for large-scale hydrogen production and efficient future in energy technology.