Water-soluble nickel and iron salts for hydroxymethylfurfural (HMF) and water oxidation: the simplest precatalysts?

Abstract

Electrochemical production of large-scale chemicals and fuels is critical to reaching carbon neutrality. However, the required anodic oxidation reactions, namely the oxygen evolution reaction (OER) or the oxidation of organics into value-added products, suffer from large overpotentials. To address this challenge, researchers have been widely investigating non-water-soluble (pre)catalysts to operate in the aqueous electrolyte. On the contrary, in this work, we approach a rapid, easy, and green carbon cloth electrode preparation using merely water-soluble nitrate precursors and ethanol as chemicals and no heating steps. The drop-coated, water-soluble transition metal salts reconstruct rapidly into the respective oxyhydroxides under OER conditions, with the oxyanion acting as a beneficial sacrificial reagent. This approach is shown herein for nickel(–iron) catalysts and their successful application for the OER (220 mV overpotential at 10 mA cm⁻², long-term stability of 40 h at 100 mA cm⁻²) and the oxidation of 5-hydroxymethylfurfural (HMF, quantitative faradaic efficiency). We compare both reactions with both electrodes closely and find that the iron-free sample is more active for the HMF oxidation in regimes where mass transport is not the main limiting factor. We anticipate that this simple electrode preparation approach can find wide application in electrocatalysis and beyond.