A method of making NiO nanoparticles is described, as well as a method of using NiO nanoparticles as an electrocatalyst component to a porous carbon electrode. The carbon electrode may be made of carbonized filter paper. Together, this carbon-supported NiO electrode may be used for water electrolysis. Using a pamoic acid salt in the NiO nanoparticle synthesis leads to smaller and monodisperse nanoparticles, which support higher current densities.