A cobalt-nickel metal-alloy thin-film sensor for hydrogen-phosphate ion

Cobalt-nickel alloy thin-films were prepared by electrodepositing on Au-coated Al₂O₃ substrate from aqueous solutions of metal-salts, and applied as a potentiometric hydrogen-phosphate ion sensor. A doping of 20 mol% nickel in cobalt contributed to enhancing hydrogen-phosphate ion sensing performances, i.e., the sensing range and response time were drastically improved. The Co₈₀Ni₂₀ thin-film electrode showed good potentiometric response to hydrogen-phosphate ion between 1.0 x 10^-5 and 1.0 x 10^-3 M with a slope of -59 mV/decade and high anion selectivity. The 90% response time to 1 mM H₂PO₄- was as short as 15 s at pH 5.0, 30°C. A mixed potential sensing mechanism could be proposed on the basis of the results. (author)