Low-cost high-efficiency system for solar-driven conversion of CO2 to hydrocarbons

Abstract

Conversion of carbon dioxide into hydrocarbons using solar energy is an attractive strategy for storing such a renewable source of energy into the form of chemical energy (a fuel). This can be achieved in a system coupling a photovoltaic (PV) cell to an electrochemical cell (EC) for CO₂ reduction. To be beneficial and applicable, such a system should use low-cost and easily processable photovoltaic cells and display minimal energy losses associated with the catalysts at the anode and cathode and with the electrolyzer device. In this work, we have considered all of these parameters altogether to set up a reference PV-EC system for CO₂ reduction to hydrocarbons. By using the same original and efficient Cu-based catalysts at both electrodes of the electrolyzer, and by minimizing all possible energy losses associated with the electrolyzer device, we have achieved CO₂ reduction to ethylene and ethane with a 21% energy efficiency. Coupled with a state-of-the-art, low-cost perovskite photovoltaic minimodule, this system reaches a 2.3% solar-to-hydrocarbon efficiency, setting a benchmark for an inexpensive all-earth-abundant PV-EC system.

Keywords: CO2 reduction; PV–EC; copper dendrites; electrocatalysis; electrolyzer.

Fig. 1.

(A) LSV of 1-cm² DN-CuO cathode (red) and anode 1 (blue), using a scan rate of 10 mV⋅s⁻¹ (currents are uncorrected for resistive losses incurred within the electrolyte; all current densities are based on projected geometric area). (B) J–E curve of the electrolyzer cell using 1-cm² DN-CuO electrodes. (C) Faradaic yields (FYs) for CO₂ reduction products using 1-cm² DN-CuO cathode at different potentials. All measurements were carried out using the electrolyzer cell described in the main text and SI Appendix, Fig. S2 using an AEM separating the cathodic (CO₂-saturated 0.1 M CsHCO₃) and anodic (0.2 M Cs₂CO₃) compartments. Constant CO₂ saturation was ensured by continuous sparging of the cathodic electrolyte with CO₂ at 2.5 mL⋅min⁻¹. FY values are detailed in SI Appendix, Table S1, and error bars are provided in SI Appendix, Fig. S8. E_cell is the electrolyzer cell potential, and E_cathode is the applied cathode potential.

Fig. 2.

Schematic view of the DN-CuO before (Top) and after (Bottom) CO₂ electroreduction in 0.1 M CsHCO₃.

Fig. 3.

STEM–high-angle annular dark-field analysis of FIB cross-sections of DN-CuO before (A and B) and after (C–E) 1-h electroreduction of CO₂ at −1.0 V vs. RHE in CO₂-saturated 0.1 M CsHCO₃. (B–D) STEM–energy-dispersive X-ray spectroscopy analyses (Cu in red, O in green). (E and F) Electron energy loss spectroscopy analysis of the axis indicated in E, identifying Cu⁰ as the main oxidation state (28) at the surface of the electrode after 1-h electroreduction of CO₂ at −1.0 V vs. RHE in CO₂-saturated 0.1 M CsHCO₃.

Fig. 4.

(A) Current–potential characteristic of the perovskite minimodule under 1 sun, AM 1.5G illumination (black squares) and measured operating current of the electrolyzer cell (geometric areas of cathode, 0.35 cm², and anode, 0.85 cm²; current measured after 5-min electrolysis) at various potentials (red dots). (B) Electrolyzer cell current as a function of photoelectrolysis time using the perovskite minimodule as the sole energy source.