Joule heating synthesis of NiFe alloy/MoO2 and in-situ transformed (Ni,Fe)OOH/MoO2 heterostructure as effective complementary electrocatalysts for overall splitting in alkaline seawater

Abstract

Designing highly-efficient and stable bifunctional seawater splitting electrocatalyst is fascinating, but still face challenges. Guided by unique interfacial properties within heterostructures, we herein reported on a rapid Joule heating method to integrate NiFe alloy on surface of MoO2 as a bifunctional electrocatalyst for seawater splitting. Benefited from the synergistic effects at interfaces of NiFe alloy/MoO2 (denoted as FeMoNi/NF), as-prepared samples exhibited Pt similar HER activity (20 mV @ 10 mA cm−2) in alkaline seawater. Moreover, surface reconstruction could occur on NiFe alloy to generate active (Ni,Fe)OOH/MoO2 heterojunction under OER conditions, which achieved superior activity (250 mV @ 50 mA cm−2) in alkaline seawater. Notably, with the rapid Joule heating, the FeMoNi/NF showed face-centered cubic phase for Fe0.5Ni0.5 alloy, which could further modulate the Fe-Ni bonds, improve electrical conductivity and provide more oxygen defects, thus causing better electrochemical properties than FeMoNi/NF-C (synthesized by conventional method). Of particular note, the extremely low cell voltage (1.45 V @ 10 mA cm−2) without IR compensation was obtained for practical membrane electrode assembly (MEA) electrochemical reactor. In addition, with the introduction of FeMoNi/NF, corresponding high solar-to-hydrogen (STH) conversion efficiency is up to 12.47 % for photovoltaic (PV)-assisted water electrolysis system under simulated sun (AM 1.5-G 100 mW·cm−2) illumination. DFT calculations demonstrated the synergetic interactions at the interfaces of alloy-metal oxides as well as the mechanistic research on catalytic sites towards HER/OER.