A monolithic and standalone solar-fuel device having comparable efficiency to photosynthesis in nature

Abstract

The need for developing sustainable energy sources has generated academic and industrial attention in artificial photosynthesis, inspired by the natural process. In this study, we demonstrate a highly efficient solar energy to fuel conversion device using CO₂ and water as feedstock. We developed a thin film photovoltaic technology for the light absorbing component using a low cost, solution based Cu(In_xGa_1−x)(S_ySe_1−y)₂ (CIGS) module fabrication method to provide sufficient potential for the conversion reactions. Our solar-fuel device uses cobalt oxide (Co₃O₄) nanoparticle thin film deposited with a low temperature coating method as the water oxidation catalyst and nanostructured gold film as the CO₂ reduction to CO generation catalyst. We demonstrated that the integrated monolithic device operated by energy only from sunlight, in an absence of any external energy input. The individual components showed the following abilities: solar-to-power conversion efficiency of 8.58% for the CIGS photovoltaic module photoelectrode, overpotential reduction of water oxidation with the Co₃O₄ catalyst film by ∼360 mV at 5 mA cm⁻², and Faradaic efficiency of over 90% by the nanostructured Au catalyst for CO₂ reduction to CO. Remarkably, this is the first demonstration of a monolithic and standalone solar-fuel device whose solar-to-fuel conversion efficiency from CO₂ and H₂O is 4.23%, which is comparable with that of photosynthesis in nature.