Paired Alkaline Electrolyzer with Furfural Oxidization and Hydrogen Evolution Over Noble Metal-Free Nife/Ni and Co/Mxene Catalysts

Abstract

Green hydrogen produced from water electrolysis utilizing renewable energy sources is promising for a sustainable future, however, current challenges are encountered owing to the energy-intensive oxygen evolution reaction (OER) and the potential hazards associated with the mixing of H2 and O2. To address these challenges, substituting the OER with more thermodynamic favorable aldehyde oxidation to produce carboxylic acids has attracted enormous attention. In this work, we integrated a novel two-dimensional MXene supported cobalt catalyst (Co/Mo2TiC2Tx-700) for hydrogen evolution reaction (HER) and a NiFe/Ni foam fabricated by an electrodeposition method for furfural oxidation reaction (FOR) to design a paired flow electrolyzer. In H-type half-cell tests, the NiFe/Ni foam anode catalyst demonstrated an FE of ~50% towards 2-FA with 50 mM furfural at 65 mA/cm2, which increased to ~100% with 150 mM furfural. The optimized Co/Mo2TiC2Tx-700 cathode catalyst exhibited remarkable HER performances: 100% FE to H2, and low overpotential of 243.99 mV, 320.56 mV at 100 mA/cm2 and 400 mA/cm2, respectively. These can be attributed to high conductivity, stability of MXene substrate, large surface area of Co-nanoparticles, and the special metal-support interaction (SMSI) between MXene and Co. A two-electrode flow cell (4 cm2) was then constructed for the concurrent electrochemical furfural oxidation and hydrogen evolution. Remarkably, Co/Mo2TiC2Tx-700 outperformed a commercial Pt/C electrode with the same loading of 0.5 mg-metal/cm2 by lowering cell voltage by 150 mV at a high current density of 300 mA/cm2, while maintaining the FE-to-H2 at >90%. The overall faradaic efficiency increased from 144% to 151% at an industrial-relevant current density of 400 mA/cm2 at a cell voltage of 3.582 V and 3.899 V for the electrolyzer with the Pt/C and Co/Mo2TiC2Tx-700 cathode, respectively.

Keywords: furfural, hydrogen production, alkaline electrolysis, noble metal-free, MXenes, electrocatalysis