Development of the Microbial Electrolysis Desalination and Chemical-Production Cell for Desalination as Well as Acid and Alkali Productions

By combining the microbial electrolysis cell and the microbial desalination cell, the microbial electrolysis desalination cell (MEDC) becomes a novel device to desalinate salty water. However, several factors, such as sharp pH decrease and Cl^– accumulation in the anode chamber, limit the MEDC development. In this study, a microbial electrolysis desalination and chemical-production cell (MEDCC) was developed with four chambers using a bipolar membrane. Results showed that the pH in the anode chamber of the MEDCC always remained near 7.0, which greatly enhanced the microbial activities in the cell. With applied voltages of 0.3–1.0 V, 62%–97% of Coulombic efficiencies were achieved from the MEDCC, which were 1.5–2.0 times of those from the MEDC. With 10 mL of 10 g/L NaCl in the desalination chamber, desalination rates of the MEDCC reached 46%–86% within 18 h. Another unique feature of the MEDCC was the simultaneous production of HCl and NaOH in the cell. With 1.0 V applied voltage, the pH values at 18 h in the acid-production chamber and cathode chamber were 0.68 and 12.9, respectively. With the MEDCC, the problem with large pH changes in the anode chamber was resolved, and products of the acid and alkali were obtained

Urine Treatment in a Stacked Membraneless Direct Urea Fuel Cell with Honeycomb-like Nickel–Molybdenum Bimetal Phosphide as the Anodic Electrocatalyst

The aim of this study was to synthesize a novel catalyst for urea oxidation and to test a stacked membraneless direct urea fuel cell (DUFC) with raw urine as fuel. The molybdenum nickel phosphides on nickel foam (MoNiP/NF) were synthesized using a combined hydrothermal and phosphating method. The honeycomb-like MoNiP/NF catalyst with a Mo/Ni molar ratio of 0.50 (i.e., MoNiP/NF-0.50) showed the highest electrocatalytic activity for urea oxidation among different catalysts. The stacked membraneless DUFC was constructed using the MoNiP/NF-0.50 electrode as anode and a gas diffusion cathode. With the electrode spacing of 5 mm and 6 electrode pairs, the stacked membraneless DUFC had a maximum voltage of 0.55 V and a power density of 0.115 mW cm–2 at the external resistance of 1000 Ω, at which the power output was 5.32 times higher than that in the individual membraneless DUFC. The urea removal reached 65.8% in the cell at the external resistance of 100 Ω within 192 h. The excellent performance of the cell could be attributed to the high activity of the MoNiP/NF-0.50 catalyst, small electrode spacing, and multiple electrode pairs. Our results should provide promising potential for scalable DUFC with efficient urine treatment

Structure Effects of 2D Materials on α‑Nickel Hydroxide for Oxygen Evolution Reaction

To engineer low-cost, high-efficiency, and stable oxygen evolution reaction (OER) catalysts, structure effects should be primarily understood. Focusing on this, we systematically investigated the relationship between structures of materials and their OER performances by taking four 2D α-Ni­(OH)₂ as model materials, including layer-stacked bud-like Ni­(OH)₂-NB, flower-like Ni­(OH)₂-NF, and petal-like Ni­(OH)₂-NP as well as the ultralarge sheet-like Ni­(OH)₂-NS. For the first three (layer-stacking) catalysts, with the decrease of stacked layers, their accessible surface areas, abilities to adsorb OH^–, diffusion properties, and the intrinsic activities of active sites increase, which accounts for their steadily enhanced activity. As expected, Ni­(OH)₂-NP shows the lowest overpotential (260 mV at 10 mA cm^–2) and Tafel slope (78.6 mV dec^–1) with a robust stability over 10 h among the samples, which also outperforms the benchmark IrO₂ (360 mV and 115.8 mV dec^–1) catalyst. Interestingly, Ni­(OH)₂-NS relative to Ni­(OH)₂-NP exhibits even faster substance diffusion due to the sheet-like structure, but shows inferior OER activity, which is mainly because the Ni­(OH)₂-NP with a smaller size possesses more active boundary sites (higher reactivity of active sites) than Ni­(OH)₂-NS, considering the adsorption properties and accessible surface areas of the two samples are quite similar. By comparing the different structures and their OER behaviors of four α-Ni­(OH)₂ samples, our work may shed some light on the structure effect of 2D materials and accelerate the development of efficient OER catalysts