Photo-Electrochemical Conversion of CO2 Under Concentrated Sunlight Enables Combination of High Reaction Rate and Efficiency

Photo-electrochemical production of solar fuels from carbon dioxide, water, and sunlight is an appealing approach. Nevertheless, it remains challenging to scale despite encouraging demonstrations at low power input. Higher current densities require notable voltage input as ohmic losses and activation overpotentials become more significant, resulting in lower solar-to-CO conversion efficiencies. A concentrated photovoltaic cell is integrated into a custom-made heat managed photo-electrochemical device. The heat is transferred from the photovoltaic module to the zero-gap electrolyzer cell by the stream of anodic reactant and produce synergetic effects on both sides. With solar concentrations up to 450 suns (i.e., 450 kW m⁻²) applied for the first time to photo-electrochemical reduction of CO₂, a partial current for CO production of 4 A is achieved. At optimal conditions, the solar-to-CO conversion efficiency reaches 17% while maintaining a current density of 150 mA cm⁻² in the electrolyzer and a CO selectivity above 90%, representing an overall 19% solar-to-fuel conversion efficiency. This study represents a first demonstration of photo-electrochemical CO₂ reduction under highly concentrated light, paving the way for resource efficient solar fuel production at high power input.