MXene-Mediated RuCo Heterostructures with Built-In Electric Field Enable High-Efficiency Hydrogen Evolution toward Seawater-Based Self-Powered Energy Systems

Abstract

The pursuit of low-cost, efficient, and durable electrocatalysts for the hydrogen evolution reaction (HER) is crucial to advancing sustainable green hydrogen production. Herein, we tailor the RuCo alloy electronic structure via an MXene-mediated reconstruction strategy for the resultant RuCo-MXene heterostructure electrocatalyst supported on pretreated cobalt foam (denoted as RuCo-MXene-Co/CF) with a strong built-in electric field (BIEF) to enable high-current-density HER in alkaline seawater for self-powered energy devices. The optimized catalyst achieves overpotentials of only 118 and 202 mV to deliver current densities of 100 and 500 mA·cm–2 in alkaline freshwater and 139 and 222 mV to reach 100 and 400 mA·cm–2 in alkaline seawater. Systematic experiments and density functional theory (DFT) calculations reveal that the remarkable HER performance stems from two synergistic effects: (i) trace Co doping into the Ru matrix reduces the water dissociation barrier and optimizes hydrogen adsorption; and (ii) a pronounced BIEF at the RuCo-MXene heterointerface, driven by the Fermi-level difference, boosts electron transfer and promotes nucleophilic region formation. Consequently, these cooperative effects effectively lower the kinetic barriers for both water dissociation and hydrogen adsorption steps. Furthermore, the RuCo-MXene-Co/CF||RuO2-Co/CF electrolyzer delivers 100 mA·cm–2 at low cell voltages of 1.64 V (alkaline freshwater) and 1.68 V (alkaline seawater) with excellent durability. An integrated Zn-H2O/seawater battery built on this electrolyzer delivered peak power densities of 5.7 and 3.9 mW·cm–2 and powered a self-driven water splitting unit, demonstrating off-grid feasibility. This work provides key insights into interfacial electric field effects and establishes a practical pathway toward efficient self-powered energy systems.