Research work  demonstrates photoelectrochemical (PEC) synthesis of hydrocarbons by coupling a structured copper nanoflower catalyst with a high photovoltage perovskite light absorber.

• Geometric surfaces a local current densities are key to management C2 hydrocarbon selectivity.
• Unassisted perovskite-silicon PEC devices coupling aqueous CO2 reduction with glycerol oxidation achieve Faradaic yields of ethane and ethylene between 5 % and 10 %, which corresponds to the optimal selectivity observed for copper nanoflower electrodes.

PEC systems offer a sustainable alternative for the direct production of C2 hydrocarbons from small building blocks such as CO2 or H2O.

• These systems integrate light harvesting and catalysis into a single panel that operates under harmless conditions.
• This reduces intermediate steps and CO2 emissions from industrial processes.

Research has demonstrated that tandem devices with robust BiVO4 and TiO2 photoanodes couple ethane and ethylene production with O2 evolution.

• The partial current densities of C2 were improved 200-fold by interfacing perovskite photocathodes with Si photoanodes for GOR.
• This provides a proof-of-concept demonstration for simultaneous PEC synthesis of hydrocarbons and organic synthesis.

Optimized copper nanoflower (CuNF) electrocatalyst was used for CO2 reduction based on its promising activity towards ethylene synthesis.

• The catalyst consisted of 2–4 µm wide clusters that preserved the 50 nm thin nanoplatelet structure of CuO.
• Such hierarchical, porous structures are known to promote CO2 reduction by increasing local pH and thus reducing proton availability for competing H2 evolution.

It was found that the C2 selectivity of integrated photocathodes strongly depends on the geometric area of the catalyst.

• Optimal selectivity towards ethane and ethylene production was obtained for an active catalyst area of ~4 mm2.
• The finding suggests that current density affects selectivity.

Photocathodes tested at different applied potentials also followed similar trends in the FY of C2 hydrocarbon products as the dark CuNF electrodes..

To overcome the thermodynamic limitations of water oxidation, perovskite photocathodes were interfaced with Si photoanodes for GOR..

• The Sip-PVK|CuNF and SiNW-PVK|CuNF devices exhibited similar selectivities and initial photocurrents.
• The partial C2 current densities of SiNW-PVK|CuNF (4 mm2) devices reached 155 µA cm−2, representing a 200-fold improvement over perovskite-BiVO4 artificial sheets coupling C2 hydrocarbon production with water oxidation.

In conclusion, this work demonstrates the versatility of integrated PEC systems for multicarbon synthesis and conversion of biomass waste into value-added products. Spring

Glossary of Key Terms

• Photoelectrochemical (PEC) synthesis: A process for direct fuel synthesis using solar energy that combines light absorption and catalysis.
• Perovskites: Semiconductor materials that exhibit high light absorption and photovoltaic properties.
• Faradaic Yield (FY): The efficiency with which electrons transferred in an electrochemical reaction lead to the formation of a specific product. Expressed as a percentage.
• Overpotential: The additional potential required beyond the thermodynamic potential to carry out an electrochemical reaction at a significant rate.
• Reversible Hydrogen Electrode (RHE): A standard reference electrode used in electrochemistry, especially in the study of hydrogen-related reactions.
• Copper Nanoflower (CuNF): A structured copper-based catalyst that exhibits high activity in CO2 reduction.
• Glycerol Oxidation Reaction (GOR): An alternative anodic reaction to the oxygen evolution reaction, in which glycerol is oxidized to valuable chemicals, thereby reducing the overall potential required for the PEC process.
• BiVO4: Bismuth vanadate, a semiconductor material used as a photoanode for the oxygen evolution reaction.
• TiO2: Titanium dioxide, a semiconductor material used as a photoanode.
• Photoanode: The electrode in an electrochemical cell where light-driven oxidation takes place.
• Photocathode: The electrode in an electrochemical cell where light-driven reduction takes place.
• Si nanowire (SiNW): Silicon nanowire used as a photoanode for glycerol oxidation.
• Bipolar membrane: A membrane used to separate the anode and cathode compartments that only transmits proton or hydroxyl ions.
• Current density: The amount of current per unit area of the electrode, typically expressed in mA cm-2.
• Electrocatalysis: Catalysis of electrochemical reactions, usually on the surface of an electrode.
• PEC tandem device: A device consisting of a photocathode and a photoanode, interconnected to perform an overall reaction, such as CO2 reduction and water/glycerol oxidation.
• Open-circuit voltage (VOC): The voltage difference between the terminals of a device when it is not connected to any external circuit.
• Short-circuit current (ISC): The amount of current produced by a device when the terminals are connected together.
• Fill factor (FF): A parameter that evaluates the quality and efficiency of a solar cell.
• AM1.5G: Standard solar spectrum used in testing solar devices.