Bifunctional Nickel Cobalt Phosphorus Sulfide Electrocatalyst for Simultaneous Hydrogen Evolution and 5-Hydroxymethylfurfural Oxidation

The replacement of the O₂ evolution reaction of electrocatalytic water splitting with a thermodynamically more favorable reaction has attracted considerable attention for simultaneous value-added feedstock formation coupled with H₂ production. The electrocatalytic oxidation of renewable biomass platform chemical 5-hydroxymethyl furfural (HMF) to 2,5-furandicaroxylic acid (FDCA), a valuable bio-monomer of polyethylene furanoate (PEF), has emerged as a promising sustainable route for biomass valorization. In this work, bifunctional nickel cobalt phosphorous sulfide nanosheet arrays (NCPS) were constructed on Ni foams as the electrodes of a two-electrode electrolytic H cell for simultaneous electrocatalytic hydrogen evolution and HMF oxidation (HMFOR) to FDCA in 0.1 m KOH. With the addition of 5 mM HMF in the electrolyte, the cell voltage required to afford the current density of 10 mA cm^-2 is less 153 mV than water electrolysis. It indicates the superior energy conversion efficiency of NCPS for electrocatalytic HER and HMFOR compared to water splitting. The amounts of H₂ and FDCA produced over NCPS in the two-electrode configuration were measured at a constant cell voltage of 2.12 V (the anode potential of 1.6 V vs. RHE) for 78 min to pass the charge of ~ 34.8 C. In the anodic chamber of the H cell, the HMF conversion is 95.01%, and the selectivity for forming FDCA is 89.06% with the Faradaic efficiency of FDCA is 86.83%. The generated H₂ in the cathodic chamber reaches a Faradaic efficiency of 96.07%. The XPS analyses indicate that the Ni²⁺/Ni³⁺ and Co²⁺/Co³⁺ ratios in the NCPS couples alter after the HER and HMFOR, suggesting that the Ni and Co cites play crucial roles in the electrocatalytic reactions. The influences of chemical and electronic structures on the electrocatalytic activity of NCPS will be discussed in this presentation.