Reactivity and Mechanism of Photo- and Electrocatalytic Hydrogen Evolution by a Diimine Copper(I) Complex

Abstract

The tetrahedral copper(I) diimine complex [Cu(pq)2]BF4 displays high photocatalytic activity for the H2 evolution reaction with a turnover number of 3564, thus representing the first type of a Cu(I) quinoxaline complex capable of catalyzing proton reduction. Electrochemical experiments indicate that molecular mechanisms prevail and DFT calculations provide in-depth insight into the catalytic pathway, suggesting that the coordinating nitrogens play crucial roles in proton exchange and hydrogen formation.

Electrocatalytic CO2 Reduction and H2 Evolution by a Copper (II) Complex with Redox-Active Ligand

“…Beyond this finding, in the absence of complex 1, the current density at −1.97 V is negligible, which suggests that no catalytic reaction occurs without complex 1. According to Equation (1), Equations (S1) and (S2), the calculated TOF of H 2 evolution is 0.33 s −1 , and FE is shown in Figure S16 (Supplementary Materials), which is comparable with those reported copper based homogeneous catalysts [8,[32][33][34].…”

“…Beyond this finding, in the absence of complex 1, the current density at −1.97 V is negligible, which suggests that no catalytic reaction occurs without complex 1. According to Equation (1), Equation (S1), and (S2), the calculated TOF of H2 evolution is 0.33 s −1 , and FE is shown in Figure S16 (Supplementary Materials), which is comparable with those reported copper based homogeneous catalysts [8,[32][33][34]. Moreover, the rinse test conducted on the FTO glass electrode after electrocatalysis shows almost no current density, which resembles that of the blank test before the catalysis (Figure 8), revealing that complex 1 can homogeneously catalyze H + reduction with high stability.…”

“…In 2021, Lan et al reported a copper (I) based complex with excellent electrocatalytic selectivity for CO 2 -to-CH 4 reduction, which occurs because of the chalcophile interactions in crystalline catalysts [7]. Mitsopoulou and coworkers investigated the electrocatalytic activity for hydrogen evolution of a Cu (I) diimine complex, and they found that the coordinated nitrogen atoms play an important role, while Yang's group developed a copper (0) enriched material to tune the syngas production with great electrochemical activity [8,9].…”

Tetrahedral Cu(I) complexes as electrocatalysts for the reduction of protons to dihydrogen gas

“…The use of [Cu(pq) 2 ][BF 4 ] (pq : quinoxaline) as both photocatalyst and electrocatalyst has only recently been studied where reduction of trifluoroacetic acid was observed in dimethylformamide at an overpotential of 0.72 V. Interestingly instead of the Cu(I) center, the pq ligand is proposed to be more heavily involved in the protonation and electrochemical reduction steps. [24] As most catalysts go through a reduction process during the catalytic cycle, we reason that Cu(II) compounds are likely to reduce to Cu(I) at some stage of the cycle. This has led us to prepare some Cu(I) complexes as the starting material so that their role in the hydrogen evolution process can be explored and evaluated.…”

“…However, there have been much fewer reports of Cu (I) compounds acting as proton reduction catalysts or catalytic precursors. The use of [Cu(pq) 2 ][BF 4 ] (pq : quinoxaline) as both photocatalyst and electrocatalyst has only recently been studied where reduction of trifluoroacetic acid was observed in dimethylformamide at an overpotential of 0.72 V. Interestingly instead of the Cu(I) center, the pq ligand is proposed to be more heavily involved in the protonation and electrochemical reduction steps [24] …”