Abstract: Developing efficient non-noble metal catalysts is crucial for reducing costs and addressing the scarcity issues associated with noble-metal-based electrocatalysts for water splitting. In this study, metal-organic frameworks-derived C, N-doped In₂O₃ with abundant oxygen vacancies were synthesized by pyrolysis of NH₂-MIL-68(In). To enhance its performance, 3D flower-like xGd₂MoO₆ (x = 10, 20, 30, 40, and 50 wt%) was integrated with In₂O₃ and 5 % MXene, forming a composite denoted as x-GInMx. The bifunctional 4-GInMx@nickel foam (NF) electrocatalyst exhibited outstanding performance, achieving low hydrogen evolution reaction (HER) overpotentials (η) of 110 and 104 mV with Tafel slopes of 83 and 76 mV/dec at current density (J) of 10 mA/cm² in alkaline freshwater (FW) and natural seawater (SW), respectively. Additionally, it demonstrated low oxygen evolution reaction (OER) η of 160 and 200 mV, along with Tafel slopes of 97 and 77 mV/dec in FW and SW, respectively. Notably, 4-GInMx@NF outperformed IrO₂@NF and approached the performance of Pt/C@NF, while also demonstrating excellent stability in corrosive SW environments. The overall water-splitting electrolyzer assembled with 4-GInMx@NF||4-GInMx@NF electrode achieved low cell voltages of 1.56 (FW) and 1.62 V (SW) at 10 mA/cm², outperforming the benchmark Pt/C@NF||IrO₂@NF electrolyzer. Additionally, density functional theory calculations provide evidence of improved catalytic activity and reaction kinetics of the GInMx heterostructures by analyzing the underlying HER and OER pathways. The exceptional performance of 4-GInMx is attributed to its high surface area, synergistic effects, multiple active sites, enhanced electrical conductivity, and resistance to structural degradation. This work highlights 4-GInMx as a promising, cost-effective bifunctional electrocatalyst for sustainable H₂ production, reduced carbon emissions, and enhanced environmental protection.

Key words: Electrocatalyst, C, N-doped In₂O₃, Gd₂MoO₆, MXene, HER and OER, Seawater water splitting