Promoting electrocatalytic hydrogenation of 5-hydroxymethylfurfural using buffer electrolytes as proton-donating motifs: Theoretical predictions and experimental validations

Abstract

Electrocatalytic hydrogenation (ECH) represents a promising alternative to conventional hydrogenation techniques with high-pressure H2 as a reductant. The proton-donating motif is an important factor governing the reaction efficiency but is usually overlooked in the ECH process. Herein, on the basis of density functional theory (DFT) predictions and experimental validations, we demonstrate that proton-buffer salts such as phosphate, carbonate and borate can greatly promote ECH efficiency. The DFT results predict that the buffer species can outperform water in donating protons for *CO hydrogenation into *C-OH via the Langmuir-Hinshelwood or proton-coupled electron transfer (PCET) mechanism, thus promoting the hydrogenation of carbonyl compounds. The experimental results demonstrate that with the buffer-promoting effects, 5-hydroxymethylfurfural (HMF) can be effectively converted at an efficiency of 96 % into the value-added 2,5-dihydroxymethylfuran (DHMF) with a yield of 80 % over cobalt oxide (Co3O4) nanoarray catalysts under near-neutral buffer electrolyte. In situ Raman analysis and kinetic isotope experimental results reveal that the real mechanism is a combined Langmuir-Hinshelwood and PCET process. Such a buffer-promoting strategy also exhibits wide applicability in ECH of various other carbonyl compounds with different electrode catalysts. This work may provide a deep understanding of the ECH process and open up new opportunities to design effective systems for the conversion of HMF into value-added products.