Two-dimensional conjugated metal-organic frameworks as electrocatalysts for boosting glycerol upgrading coupled with hydrogen production

Renewable electricity-driven valorisation of glycerol is recognised as an effective and alluring approach to generate high value-added compounds from biomass by-products. Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) are promising for electrocatalysis due to their diverse and predictable structures, high electronic conductivity, and efficient utilisation of well-defined active centers. Herein, we report the first systematic investigation of 2D c-MOFs with Ni-X4 (X = O or N) moieties for glycerol oxidation reaction (GOR) to investigate factors impacting both electrocatalytic activity and selectivity. The study involves [Ni3(HHTQ)2]n (HHTQ = 2,3,7,8,12,13-hexahydroxytricycloquinazoline), [Ni3(HHTP)2]n (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene), [Ni3(HITP)2]n (HITP = 2,3,6,7,10,11-hexaiminotriphenylene), and [Ni3(HATI)2]n (HATI = 2,3,7,8,12,13-hexaiminotriindole), revealing superior GOR performance of Ni3(HHTQ)2. In situ-13C electrochemical nuclear magnetic resonance (NMR) and Raman spectroscopies provide insights into the GOR mechanism and identify Ni-O4 sites as active centers. Theoretical exploration further demonstrates that the high GOR activity of Ni3(HHTQ)2 originates from strong adsorption of intermediates and weak interlayer interactions, which improve the transfer process and overall kinetics. Our research proves the feasibility of exploiting 2D c-MOFs as remarkable GOR catalysts, opening up an inspiring avenue for the elaborate design of advanced electrocatalysts, which is of great significance for the development of renewable energy conversion and storage technologies.