Ni-ferrite with structural stability for solar thermochemical H2O/CO2 splitting

At present, the quest for alternative green energy sources is being steered by the punitive side effects of excessive use of carbon-based energy sources. The cheapest yet most logical solution to this problem is the adoption of renewable energy sources and increased energy conversion. Solar energy is the largest exploitable renewable resource, however, the efficient conversion of solar energy into chemical energy poses a challenge. Over the years, researchers have discovered that concentrated solar energy can be economically employed to power the two step redox thermochemical splitting cycles, which utilize water and / or carbon dioxide as the reactants for the production of exploitable fuels i.e. hydrogen and or carbon monoxide. Recent studies have revealed that specific pairs of ferrites, such as those of nickel and cobalt, can be employed. Unfortunately, this process is effective only at very high temperature which in no time melts the oxides utilized, thereby reducing the available reaction specific area hence diminishing the activity of the redox pair. Fortunately, enhanced performance for the desired reactions can be achieved if the ferrites are dispersed on highly thermostable materials.

To this note, a team of researchers led by Dr. Lori Nalbandian from the Chemical Process and Energy Resources Institute at Center for Research and Technology Hellas in Greece prepared nickel-based ferrite samples with improved thermal stability, which conserve sufficient porosity and surface area after extensive high temperature treatment and multiple redox cycles, by combining the beneficial effects of adding zirconia and pore forming agents. Their work is currently published in International journal of hydrogen energy.

Briefly, the research method employed commenced by addition of zirconia to the Ni-Ferrite samples. Subsequently, the research team added different concentrations of different sacrificial materials (polyethylene glycol and carbon black) so as to create a high porosity. They then studied the effects of the zirconia and pore former agent concentrations on the porosity and the activity of the samples during redox cycles. Eventually, the porosity retention as well as the activity of the best of the prepared samples were compared to the corresponding porosity and activity of pure Ni-Ferrite samples prepared by the same methods, without the addition of zirconia and sacrificial materials.

After physicochemical characterization and activity evaluation of the prepared samples, the authors of this paper mainly observed that the highest thermal stability and conservation of porosity were obtained with 20% by weight of carbon black and zirconia content 10-30% by weight. In addition, they noted that the pores of samples that were prepared with addition of carbon black had both high volume and smaller diameters, thus enhanced activity.

The study has successfully presented the synthesis of porous Ni-Ferrite materials with improved thermal stability at temperatures up to 1450 ⁰C using a conventional ceramic processing route. To this end, the work has proven that the samples with the highest porosity and optimum pore size distribution have the highest capability to reversibly deliver and pick up their lattice oxygen.