Identifying an Alternative Hydride Transfer Pathway for CO₂ Reduction on CdTe(111) and CuInS₂(112) Surfaces

Abstract

To ascertain if CdTe(111) and CuInS2(112) photoelectrodes exhibit the same carbon dioxide (CO2) reduction mechanism as found for GaP, with adsorbed 2‐pyridinide (2‐PyH–*) as active intermediate, the feasibility of 2‐PyH–* formation on these surfaces must be assessed. Via density functional theory, we conclude that although thermodynamically possible, 2‐PyH−* formation on CdTe(111) or CuInS2(112) is hindered kinetically. A different CO2 reduction pathway, distinct from GaP's mechanism, must be operative. We predict that surface hydride (H−*) readily forms on CdTe(111) and CuInS2(112) and direct surface hydride transfer (HT) to CO2 dominates over transfer to adsorbed pyridine (Py*). Direct HT to CO2 has a large thermodynamic driving force and zero activation barrier on both surfaces. This reaction becomes slightly more spontaneous with adjacent Py* on both surfaces, rationalizing experiments where Py slightly enhances CO2 reduction on CdTe and CuInS2. We thus conclude, Py is largely a spectator in CO2 reduction on these electrodes, unlike its key role as hydride shuttle on GaP. HT from H−* to CO2 also competes effectively with hydrogen evolution on these two surfaces, explaining the observed selectivity for CO2 reduction over hydrogen evolution. Finally, formic acid readily adsorbs on CuInS2(112), which may facilitate the observed methanol formation.

Investigation of Pyridine as a Cocatalyst for the CO2 Reduction Reaction on the Cu2O Cathode Surface

“…A noninteger charge Q was assigned to the core of the pseudo-H atoms. Q = Z / N , where Z is the valence electron number of the atom replaced by the pseudo-H atom (here the valence electrons refer to those participating in the bonds between Cu and O ions), and N is the number of bonds associated with the replaced atom in the bulk structure. ,, In our slab model, Z = 6 and N = 4; thus Q = 1.5 for each of the three pseudo-H atoms binding to the bottom Cu atoms mimicking O, while Z = 1, N = 2, and Q = 0.5 for each of the three pseudo-H atoms binding to the bottom O atoms mimicking Cu. The top surface of the stoichiometric slab model exposes coordinatively unsaturated oxygen (O CUS ) and copper (Cu CUS ) ions.…”

“…Vibrational free energy corrections were included in this work. We calculated free energies as G = E 0K + ZPE + Δ H – T Δ S ( T = 300 K), , where well-established statistical mechanical expressions were used to calculate vibrational free energy correction terms. E 0K is the DFT 0 K total energy, ZPE means the zero-point energy, Δ H is the enthalpy change from 0 to 300 K, and Δ S is the vibrational entropy change from 0 to 300 K. We substituted DFT-derived vibrational frequencies into the free energy correction calculation scheme based on the vibrational partition function under the harmonic oscillator approximation.…”

Recyclable Copper Indium Sulfide Quantum Dots for Photocatalytic Homocoupling of Arenediazonium Tetrafluoroborates

“…It can provide photoluminescence (PL) emission ranging from the visible to the region, and have broad absorption, large light absorption coefficient, and chemical stability. 49,50 Accordingly, CuInS 2 QDs have been successfully applied in numerous fields including water splitting, 51 pollutant degradation, 52 H 2 production, 53 and CO 2 reduction, 54 biological activity. 55 However, as far as we know, there are few reports on the application of CuInS 2 QDs as a photocatalyst in organic synthesis.…”

“…In the past decades, photochemistry has been proved to be an efficient and versatile tool for organic synthesis because of its advantages of simple operation, low energy consumption, environmental friendliness, compatible functional groups, and mild conditions. − Especially, heterogeneous photocatalysis has attracted more and more attention because of its advantages of easy separation and reuse, high thermal stability, and physical and chemical stability. − Among them, cheap and recyclable semiconductors represent an attractive alternative photocatalyst. − CuInS 2 QDs are a direct transition semiconductor with a suitable band gap energy of about 1.53 eV and do not contain any toxic heavy metals. It can provide photoluminescence (PL) emission ranging from the visible to the region, and have broad absorption, large light absorption coefficient, and chemical stability. , Accordingly, CuInS 2 QDs have been successfully applied in numerous fields including water splitting, pollutant degradation, H 2 production, and CO 2 reduction, biological activity . However, as far as we know, there are few reports on the application of CuInS 2 QDs as a photocatalyst in organic synthesis .…”

Metal surfaces catalyze polarization-dependent hydride transfer from H2

“…Exposing the intrinsic thermodynamic and kinetic factors controlling interfacial hydride transfer requires the separation of this reaction step from other competing reactions. Owing to all these complexities, the hydride transfer reactivity of surface M−H has been primarily investigated by computational modeling, [26][27][28][29][30][33][34][35][36] rather than direct experiments.…”