Stand-Alone Photoelectrochemical Energy Conversions

The photoelectrochemical (PEC) conversions of water and atmospheric CO₂ to value-added fuels, such as H₂, CH₄, and CH₃OH, can provide potential alternative sources for clean and environment-friendly solar fuels. Several efforts are reported on the designing and developing stand-alone PEC cells that efficiently produce H₂ and O₂ from water and minimize atmospheric CO₂ via conversion to fuels under only sunlight. However, in reality, high overpotential, poor product-selectivity, competitive side-reactions, and self-reduction of a catalyst limit the performance of the PEC cells, thereby requiring high power inputs. The choice of electrode materials and architectures of PEC cells are very important for designing stand-alone and durable PEC cells with high solar-to-fuels conversion efficiency (Eff_STF) and high selectivity. The present review provides a complete account of recent published works on stand-alone PEC systems with different architectures; development of electrode materials for high Eff_STF, selectivity, and stability; and the current challenges. Furthermore, this review describes the future outlook on stand-alone PEC systems for future production of clean solar fuels and mitigation of atmospheric CO₂ levels by utilizing only solar energy.