Hydrogen production by HI decomposition over nickel–ceria–zirconia catalysts via the sulfur–iodine thermochemical water-splitting cycle

• Ni/Ce0.8Zr0.2O2 catalysts were investigated for HI decomposition.
• The calcination temperature affected the properties and performance of catalysts.
• Zr4+ replaced Ce4+, and Ni2+ ions also dissolved into the ceria lattice.
• The dispersion of NiO species on the surface of catalysts was discussed.
• The main active sites were proposed for HI catalytic decomposition.

Effects of Ni/Ce0.8Zr0.2O2 catalysts with different calcination temperatures were investigated for HI decomposition in the sulfur–iodine cycle. Calcination temperature affected the properties and performance of the catalysts. The catalytic activity of Ni/Ce0.8Zr0.2O2 catalysts was higher than that of catalysts based on pure ceria. The Ni/Ce–Zr300 demonstrated the best catalytic activity for temperature below 425 °C, while the Ni/Ce–Zr700 demonstrated the best catalytic activity above 450 °C. The Ni/Ce0.8Zr0.2O2 catalysts were formed with Zr4+ replacing Ce4+ in the ceria lattice and the Ni2+ ions dissolved into the ceria lattice. The NiO species are highly dispersed in Ni/Ce–Zr300, Ni/Ce–Zr500 and Ni/Ce–Zr700, but the sintering and agglomeration occurred obviously in Ni/Ce–Zr900. Interfacial NiO sites that strongly interacted with ceria and oxygen vacancy were regarded as the main active sites in HI catalytic decomposition. The incorporation of Zr improved the catalytic performance, textual features, thermal resistance and oxygen storage/transport properties of Ce–ZrO2 mixed oxides and the corresponding catalysts.