High Efficiency Solar Desalination Accompanying Electrocatalytic Conversions of Desalted Chloride and Captured Carbon Dioxide

Abstract

The sustainability of conventional water- and energy-associated systems is being examined in terms of water–energy nexus. This study presents a high-efficiency, off-grid solar desalination system for saline water (salinities 10 and 36 g L^(–1)) that accompanies electrocatalytic oxidations of chloride and, consequently, urine via oxidized chlorine species while concomitantly producing formate from captured CO_2. A variable number of desalination cell arrays is placed between a double-layered nanoparticulate titania electrocatalyst (Ti/Ir_xTa_(1–x)O_y/nano-TiO_2; denoted as n-TEC) anode and a porous dendrite Bi cathode. A potential bias to the n-TEC and Bi pairs initiates the transport of chloride and sodium ions in the saline water to the anode and cathode cells, respectively, at an ion transport efficiency of ∼100% and a specific energy consumption of ∼1.9 kWh m^(–3). During the desalination, the n-TEC anode catalyzes the conversion of the transported chloride into reactive chlorine species, which, in turn, mediate the decomposition of urine in the anode cell. Concurrent with the anodic process, formate is continuously produced at a faradic efficiency of >95% from the CO_2 captured in the catholyte. When a photovoltaic cell (power conversion efficiency of ∼18%) is coupled to the stack device with five desalination cells, the three independent processes synergistically proceed at a maximum overall solar-to-desalination system efficiency of ∼16% and a maximum solar-to-formate chemical energy conversion efficiency of ∼7%.