Highly selective electrosynthesis of 3,4-dihydroisoquinoline accompanied with hydrogen production over three-dimensional hollow CoNi-based microarray electrocatalysts

Electrocatalytic oxidation reaction of biomass-based derivatives is an excellent candidate to replace water oxidation for obtaining both value-added products and hydrogen (H2), but the exploration of competent electrocatalysts is still highly challenging. Herein, two new types of three-dimensional self-supported hollow microarrays containing CoNi layered double hydroxide (CoNi-LDH) and N-doped carbon nanosheets decorated with CoNi alloyed nanoparticles (CoNi-NC) on carbon cloth (CC) are prepared, which are further used as efficient electrocatalysts for tetrahydroisoquinoline (THIQ) electrooxidation and hydrogen evolution reaction (HER), respectively. We demonstrate that the Co-modulated electronic environment for Ni(II)/Ni(III) redox-looping in CoNi-LDH is the main factor to boost the selectivity of 3,4-dihydroisoquinoline (DHIQ) for the indirect electrooxidation process of THIQ. Density functional theory (DFT) calculations reveal that the Ni(III)/Co(III) dual sites of CoNi-LDH exhibit enhanced adsorption for THIQ but poorer adsorption for DHIQ compared to pure Co(III) or Ni(III). Therefore, the Ni(III)/Co(III) dual sites can effectively inhibit the peroxidation of DHIQ to isoquinoline (IQ) over CoNi-LDH, thus improving the selectivity of DHIQ to nearly 100%, much higher than that of its pure Ni counterpart. Moreover, CC@CoNi-NC can deliver high HER activity with low overpotential (40 mV@10 mA·cm−2) and high exchange current density (3.08 mA·cm−2). Impressively, the assembled flow-cell device with CC@CoNi-LDH anode and CC@CoNi-NC cathode only requires low cell voltage and electricity consumption of 1.6 V and 3.50 kWh per cubic meter of H2 (@25 mA·cm−2).