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Abstract Electrocatalytic urea removal is a promising technology for artificial kidney dialysis and wastewater treatment. Urea electrooxidation was studied on nickel electrocatalysts modified with Cr, Mo, Mn, and Fe. Mass transfer limits were observed for urea oxidation at physiological concentrations (10 mmol L). Urea oxidation kinetics were explored at higher concentrations (200 mmol L), showing improved performance, but with lower currents per active site. A simplified dialysis model was developed to examine the relationship of mass transfer coefficients and extent of reaction on flowrate, composition, and pH of the reacting stream. For a nickel hydroxide catalyst operating at 1.45 V, 37 , and pH 7.1, the model shows a minimum geometric electrode area of 1314 cm²is needed to remove 3.75 g urea h with a flow rate of 200 mL min for continuous operation. 

Intrinsic active site ensembles on Ni₂P nanocrystal surfaces direct the selective reduction of nitrate to ammonia through the potential-dependent co-adsorption of H* and NO_x*. 

Nickel-chromium-molybdenum (NiCrMo) alloys are well-known for having exceptional corrosion resistance, but their electrocatalytic properties have not been extensively studied. In this paper, the development of electro-active nickel-oxyhydroxide (NiOOH) phases and kinetics of the oxygen evolution reaction (OER) have been examined on alloys G35, B3, and C276 in alkaline electrolyte at 25 °C. Reproducible oxide layers were grown by potential cycling between 0.85 and 1.52 V vs RHE up to 600 cycles, and the transition between Ni(OH) 2 and NiOOH was monitored by cyclic voltammetry throughout. Onset potentials, Tafel slopes, and turnover frequencies (TOF) were measured at OER overpotentials between 270 and 390 mV. Alloys with dissimilar Cr:Mo ratios had significantly higher electrochemical surface area and increased γ -NiOOH formation, suggesting higher metal dissolution rates. The equal Cr:Mo concentration alloy and pure Ni developed a primarily β -NiOOH surface, and had 1.8–2.0 times larger TOF values than those containing significant γ -NiOOH. The NiCrMo alloys required smaller overpotentials (54–80 mV) to produce 10 mA cm −2 of OER current, and had comparable Tafel slopes to pure Ni. The findings here indicate a β -NiOOH-developed surface to be more OER-active than a γ -NiOOH-developed surface, and suggest certain NiCrMo alloys have promise as OER electrocatalysts.