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A robust precious metal-free photocatalyst system comprised of ligand-free ZnSe quantum dots and a phosphonic acid-functionalised Ni(cyclam) catalyst achieves efficient reduction of aqueous CO2 to CO.

A precious‐metal‐ and Cd‐free photocatalyst system for efficient H 2 evolution from aqueous protons with a performance comparable to Cd‐based quantum dots is presented. Rod‐shaped ZnSe nanocrystals (nanorods, NRs) with a Ni(BF 4 ) 2 co‐catalyst suspended in aqueous ascorbic acid evolve H 2 with an activity up to 54±2 mmol g ZnSe −1 h −1 and a quantum yield of 50±4 % ( λ =400 nm) under visible light illumination (AM 1.5G, 100 mW cm −2 , λ >400 nm). Under simulated full‐spectrum solar irradiation (AM 1.5G, 100 mW cm −2 ), up to 149±22 mmol g ZnSe −1 h −1 is generated. Significant photocorrosion was not noticeable within 40 h and activity was even observed without an added co‐catalyst. The ZnSe NRs can also be used to construct an inexpensive delafossite CuCrO 2 photocathode, which does not rely on a sacrificial electron donor. Immobilized ZnSe NRs on CuCrO 2 generate photocurrents of around −10 μA cm −2 in an aqueous electrolyte solution (pH 5.5) with a photocurrent onset potential of approximately +0.75 V vs. RHE. This work establishes ZnSe as a state‐of‐the‐art light absorber for photocatalytic and photoelectrochemical H 2 generation.

Electrolytic or solar-driven reduction of CO2 to CO using heterogenized molecular catalysts is a promising approach towards production of a key chemical feedstock, as well as mitigating CO2 emissions. Here, we report a molecular cobalt-phthalocyanine catalyst bearing four phosphonic acid anchoring groups (CoPcP) that can be immobilized on metal oxide electrodes. A hybrid electrode with CoPcP on mesoporous TiO2 (mesoTiO2) converts CO2 to CO in aqueous electrolyte solution at a near-neutral pH (7.3) with high selectivity and a turnover number for CO (TONCO) of 1949 ± 5 after 2 h controlled potential electrolysis at -1.09 V vs. SHE (~550 mV overpotential). In situ UV-visible spectroelectrochemical investigations alluded to a catalytic mechanism that involves non-rate-limiting CO2 binding to the doubly-reduced catalyst. Finally, the integration of the mesoTiO2|CoPcP assembly with a p-type silicon (Si) photoelectrode allowed the construction of a benchmark precious-metal-free molecular photocathode that achieves a TONCO of 939 ± 132 with 66% selectivity for CO (CO/H2 = 2) under fully aqueous condition. The electrocatalytic and photoelectrochemical (PEC) activity of CoPcP was compared to state-of-the-art synthetic and enzymatic CO2 reduction catalysts, demonstrating the excellent performance of CoPcP and its suitability for the integration in tandem PEC devices.

Colloidal photocatalysts are a promising, low-cost material to utilize solar light for the conversion of CO2 to carbon-based fuels, but controlling the product selectivity for CO2 reduction remains challenging, in...

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Sunlight-driven CO 2 reduction is increasingly considered as a promising approach to contribute toward a carbon-neutral fuel cycle, but most photocatalyst systems are currently studied individually under batch conditions with manual, labor-intensive analytical procedures. Here, we present the advantages of a continuous-flow setup to study photocatalytic CO 2 to CO reduction systems, which also benefits from aspects of automation (using programmed in-line gas quantification of multiple samples in parallel). The capabilities of the methodology are demonstrated using a state-of-the-art light absorber platform based on ZnSe quantum dots (QDs) in combination with a series of molecular co-catalysts based on Ni and Co for visible-lightdriven CO 2 reduction in aqueous ascorbate solution. A newly synthesized Co-tetraphenylporphyrin featuring three sulfonate groups and one amine group (Co(tppS3N1)) is identified to exhibit a benchmark photocatalytic activity (18.6 μmol of CO, 79.7 mmol of CO g ZnSe −1, TON Co (CO) of 619, external quantum efficiency (EQE) >5%). The utility of our methodology is further shown by applying the setup to study the photocatalyst systems under lower light intensities, low CO 2 concentration, and aerobic conditions, which impact the photocatalytic activity and selectivity. Overall, this work reports an improved methodology for studying photocatalytic CO 2 reduction alongside advancing the understanding of QD molecular co-catalyst hybrids using ZnSe QDs as a versatile light absorber based on earth-abundant components that operate under fully aqueous conditions.

Sunlight-driven CO2 reduction to renewable fuels is a promising strategy towards a closed carbon cycle in a circular economy. Colloidal quantum dots (QDs) have emerged as a versatile light absorber...