Ni-based metal-organic framework sensor material for urea detection: Mechanistic insights and performance

A mechanistic study of the metal-organic framework nickel-hexahydroxytriphenylene [Ni3(HHTP)2]n as an active catalyst material for electrochemical urea sensing is reported, together with the evaluation of its performance. Urea sensing is a crucial technology for the life quality of people facing kidney disease. Through the quantification of urea in saliva, the monitoring of the progress of kidney disease could be enabled. [Ni3(HHTP)2]n can detect urea via urea electro-oxidation reaction. The urea electro-oxidation on [Ni3(HHTP)2]n follows an EC' mechanism. [Ni3(HHTP)2]n is electrochemically transformed into Ni(OH)2, the catalytic intermediate of Ni in alkaline electrolyte, and the reduction step of Ni3+ to Ni2+ limited by the urea electro-oxidation reaction. The transformation leads to a disintegration of the metal-organic framework due to oxygen evolution. As urea inhibits oxygen evolution, the degradation is also inhibited. Our results demonstrated a competitive sensor when compared to the benchmarking, with a sensitivity of 1.797 mA/cm2∙mM Urea, the limit of detection of 3.5 µM, linear range between 0.01 mM and 1 mM with a correlation coefficient of 0.991 and selectivity towards Na+, K+, Cl−, creatinine, uric acid, and low concentrations of glucose.