Trifunctional noble-metal-free multi-site electrocatalysts based on NiMn-LDH/CuCo2S4/rGO for energy-saving hydrogen generation via 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 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 1.27V was required to achieve a 100mA cm-2 benchmarking 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 a 100 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 when undergoing 72-hour experiments. 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 the TOF of 0.017 s-1 and 0.124 s-1 for OER and UOR, respectively. In a two-electrode system, the NiMn-LDH/CuCo2S4/rGO||Pt/C exhibited cell voltages of 1.34 V at 10 mA cm−2 and 1.65 V at 100 mA cm−2. 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 technolog.