Decomposition of methane to produce carbon monoxide-free hydrogen is accomplished using un-supported, nanometer sized, hydrogen reduced, nickel oxide particles made by a precipitation process. A nickel compound, such as NiCl.sub.2 or Ni(NO.sub.3) is dissolved in water and suitably precipitated as nickel hydroxide. The precipitate is separated, dried and calcined to form the NiO catalyst precursor particles.