(24d) High-Efficiency Photo-Electrochemical Chloro-Alkali Production

The increased penetration of photovoltaic (PV) technologies has led to significant challenges on the management of the electrical grid. This has made evident the need for energy storage technologies that can bridge the temporal mismatch between electricity production and demand imposed by intermittent solar power sources. Alternatively, the implementation of PVs for large-scale off-grid chemical processes could further accelerate the deployment of clean energy technologies. Electrochemical processes, such as the ones implemented for chlor-alkali production, account for more than 1% of the global energy consumption and could be adapted to directly operate with solar energy sources. In this study, we demonstrate a solar chloro-alkali reactor that operates at unprecedented solar-to-chemical efficiencies as high as 25.1%. The reactor implements high efficiency multi-junction InGaP/GaAs/InGaAsNSb solar cells within a novel planar solar concentrator which maintains a ± 40^o acceptance angle with minimal tracking requirements. The concentrated PV system provides the required potential (V_OC = 3.16 V) to drive a customized electrochemical cell fabricated via additive manufacturing. The electrochemical cell is composed of a Nickel cathode and a dimensionally stable anode based on a Titanium substrate coated with an Iridium and Ruthenium oxide blend. The two electrodes are separated by a Nafion® 117 membrane which allows for the collection of nearly pure H₂ and Cl₂ gas streams as well as a NaOH enriched aqueous stream in the cathode side. Under operation conditions the faradaic efficiency towards chlorine production of the anode was measured to be between 96-99%. The demonstration presented here provides insights and foundational design principles for the implementation of solar chemical processes. Related developments for the production of solar-Hydrogen and solar-textiles will be discussed.