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 (salinity 10 and g L −1) that accompanies electrocatalytic oxidations of chloride and, consequently, urine via oxidized chlorine species, while concomitantly producing formate from captured CO2. A variable number of desalination cell arrays is placed between a double-layered nanoparticulate titania electrocatalyst (Ti/IrxTa1−xOy/nano-TiO2; denoted as n-TEC) anode and a porous dendrite Bi cathode. A potential bias to the n-TEC and Bi pair 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 Faradaic efficiency of >95% from the CO2 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 ~16% and a maximum solar-toformate chemical energy conversion efficiency of ~7%.

Electrochemical Disinfection in Water and Wastewater Treatment: Identifying Impacts of Water Quality and Operating Conditions on Performance

“…Because of the relatively high chloride concentration in urine and feces, most wastewater treatment contexts do not require any Cl – supplementation. 73 , 83 , 84 However, in most circumstances, the influent concentration of Cl – in drinking water treatment is insufficient to produce Cl 2 without an external source. 41 , 85 Unlike hydroxyl radicals or other stronger oxidants, free chlorine can react with ammonia in solution to form chloramines as described above.…”

Ion‐Enhanced Conversion of CO2 into Formate on Porous Dendritic Bismuth Electrodes with High Efficiency and Durability

“…[8,9] Given such intrinsic selectivity,t he morphology of Bi has often been tailoredi nto variouss hapes (e.g.,s heets, flakes,d endrites) by hydrothermal and electrodeposition methods. [8,13] Regardlesso ft he shape, the reported performances of Bi have been quite similari nt erms of selectivity [i.e.,f aradaic efficiency (FE) > 80 %],p artial currentd ensities forf ormate production( J FM = 2-10 mA cm À2 at E = À0.73 to À1.13 Vv s. RHE), and durability (operating time:4 -24 h) in aqueous bicarbonate solutions( 0.1-0.5 m;T able S1 and Figure S1 in the Supporting Information). The J FM values larger than the limiting current density (J8 % 6mAcm À2 ,b ased on geometric area) can be attributed to at hree-dimensional structure with al arges urface area.…”

“…For the high‐index planes of Bi, transfer of the first H + /e − pair is slow yet mildly endergonic and leads to adsorbed *OCOH (CO 2 +H + /e − →*OCOH), whereas that of the second H + /e − pair is exergonic and spontaneously releases formic acid (*OCOH+H + /e − →HCOOH) . Given such intrinsic selectivity, the morphology of Bi has often been tailored into various shapes (e.g., sheets, flakes, dendrites) by hydrothermal and electrodeposition methods . Regardless of the shape, the reported performances of Bi have been quite similar in terms of selectivity [i.e., faradaic efficiency (FE)>80 %], partial current densities for formate production ( J FM =2–10 mA cm −2 at E =−0.73 to −1.13 V vs. RHE), and durability (operating time: 4–24 h) in aqueous bicarbonate solutions (0.1–0.5 m ; Table S1 and Figure S1 in the Supporting Information).…”

Electrocatalytic arsenite oxidation in bicarbonate solutions combined with CO2 reduction to formate

“…The cross-sectional view of the samples obviously shows the sub-micrometer-thick interlayer between the underlying Ti substrate and ~5.5 m thick TiO2 overlayer. The interlayer composed of Ir and Ta was uniformly distributed throughout the Ti substrate, whereas our previous attempt led to a localized distribution of Ta [45]. The energy dispersive X-ray spectroscopic analysis of the cross-section further reveals the fractional composition of 87%, 7.6%, and 5.4% for Ti, Ir, and Ta, respectively (Fig.…”

“…Such the weak IrO2 and absent TaOx peaks could be attributed to the thick TiO2 overlayer that inhibits the penetration of the X-ray beam. The primary phase of the TiO2 overlayer was anatase at ~82% (i.e., rutile of ~18%) [45] due to a relatively low annealing temperature (425 C) (Fig. S3).…”