Preparation of hydrophobic three-dimensional hierarchical porous zinc oxide for the promotion of electrochemical CO2 reduction

The construction of three-dimensional hierarchical porous and hydrophobic-aerophilic interfaces facilitates mass transport and CO2 enrichment by kinetically accelerating the CO2 electrochemical reduction reaction (CO2RR). Inspired by the process of baking bread, in which pores that connect the interior of the bread to its exterior are created, we propose a template-free metal carbonate-porous metal oxide (MC-PMO) strategy to synthesize porous metal oxides with tunable pore size. Using this strategy, a series of porous metal oxides with different morphologies and different metals was successfully developed. Furthermore, the effect of catalyst mass transport on the CO2RR was explored. The porous catalysts with suitable pore size promoted mass transfer, which significantly enhanced the activation and transformation of CO2. In addition, based on a hydrophobic group-modified metal oxide surface (HG-MO) strategy, a hydrophobic-aerophilic interface microenvironment was constructed to reduce the water dissociation activity and effectively inhibit the hydrogen evolution reaction (HER). HP-ZnO500 @ 2-NTL was obtained by modifying hierarchical porous zinc oxide (HP-ZnO-500) with the hydrophobic 2naphthalenethiol (2-NTL). The hydrophobic surface of HP-ZnO-500 @ 2-NTL was easily enriched with CO2 gas under the influence of the "plastron effect", and the surface hydrophobic film stabilized the M-H bond. Thus, HER was suppressed. At - 1.0 V vs. RHE, HP-ZnO-500 @ 2-NTL achieved a faradaic efficiency of CO (FECO) as high as 83.0%, and displayed high catalytic activity in a wide potential range. The "MC-PMO" strategy and "HGMO" strategy reported herein are universal and are expected to guide the further preparation and modification of different metal-based porous metal oxides for sustainable CO2RR.