Aqueous Photoelectrochemical CO₂Reduction to CO and Methanol over a Silicon Photocathode Functionalized with a Cobalt Phthalocyanine Molecular Catalyst

Abstract

We report a precious‐metal‐free molecular catalyst‐based photocathode that is active for aqueous CO2 reduction to CO and methanol. The photoelectrode is composed of cobalt phthalocyanine molecules anchored on graphene oxide which is integrated via a (3‐aminopropyl)triethoxysilane linker to p‐type silicon protected by a thin film of titanium dioxide. The photocathode reduces CO2 to CO with high selectivity at potentials as mild as 0 V versus the reversible hydrogen electrode (vs RHE). Methanol production is observed at an onset potential of −0.36 V vs RHE, and reaches a peak turnover frequency of 0.18 s−1. To date, this is the only molecular catalyst‐based photoelectrode that is active for the six‐electron reduction of CO2 to methanol. This work puts forth a strategy for interfacing molecular catalysts to p‐type semiconductors and demonstrates state‐of‐the‐art performance for photoelectrochemical CO2 reduction to CO and methanol.

Multi-Electron Transfer at H-Terminated p-Si Electrolyte Interfaces: Large Photovoltages under Inversion Conditions

“…Hybrid photoelectrodes comprised of a narrow bandgap semiconductor with an integrated molecular catalyst are actively being investigated for the generation of fuels from chemical feedstocks and sunlight. − The interfacial electron transfer processes that govern the efficiency of such hybrids are understood through a model that requires isoenergetic transfer between the catalyst and photogenerated carriers at the fixed energetic position of the conduction or valence band edge. − This model was first described in the 1960s by the combined theoretical work of Marcus and Gerischer , and continued to be disseminated in modern research publications and textbooks of electron transfer theories. , This energetic requirement is suitable for optimization of single electron transfers of importance to regenerative solar cells, yet remains challenging for important multi-electron catalysis such as water oxidation and carbon dioxide reduction. Herein, we report electron transfer, photovoltage, and kinetic behavior of illuminated p-Si electrolyte interfaces in contact with redox active species that accept multiple electrons.…”

Tailoring co-catalysts on Si photocathodes for efficient photoelectrochemical CO2 reduction: recent progress and prospects of deposition methods

“…The Cu co-catalyst for multicarbon production can be applied to the Si surface using the drop-casting method. 57,58 Peidong Yang et al published a study detailing the development of SiNW photocathodes with CuNPs ensembles to facilitate efficient PEC CO 2 conversion into multicarbon products. 57 The CuNPs were affixed to the SiNWs using a dropcast-directed assembly method (Fig.…”

“…These drop-casting methods present a versatile catalyst deposition technique well-suited for applications in PEC CO 2 RR. 12,[49][50][51][52][53][54][55][56][57][58] Photo/electrodeposition involves photochemical, electrochemical, or combined processes to deposit materials onto a substrate. In photodeposition, light, typically photons, initiates crucial electrochemical reactions for material deposition on an electrode surface.…”

Investigation of the Excited-State Electron Transfer and Cage Escape Yields Between Halides and a Fe(III) Photosensitizer

“…1,18−26 Typical examples include hydrogen gas (H 2 ), which is considered worldwide as a promising target for largescale energy storage and distribution. 27 Alternative solar fuels include liquid fuels from CO 2 reduction, 8,28,29 as well as halogen (X 2 ), that could be concomitantly formed with H 2 upon hydrohalic acid (HX) splitting. 30,31 HX splitting would operate according to a mechanism depicted in Figure 1 where the excited photosensitizer oxidizes the halide (X − ), thereby forming the corresponding X • that further reacts with X − to form X 2…”