The porosity of NiCo2O4 films and powders by three common preparation techniques

• The porosity of NiCo2O4 powders prepared by three methods and corresponding films is investigated.
• NiCo2O4 is prepared by thermal decomposition, spray pyrolysis and co-precipitation.
• Thermal decomposed NiCo2O4 has negligible meso-porosity but significant macro-porosity.
• Spray pyrolysis and co-precipitation yields meso-porosity and high surface area and pore volume.
• Co-precipitation is arranged for a material particularly suited to electrochemical applications.

The spinel NiCo2O4 has been prepared as a powder and a film by three common techniques: thermal decomposition, co-precipitation and spray pyrolysis. The porous nature of these materials has been investigated by a combination of nitrogen adsorption and mercury intrusion porosimetry. It is shown that thermal decomposition yields a material of low meso-porosity with the majority of pores being confined to the macropore region. Both co-precipitation and spray pyrolysis yield powders of appreciable BET surface area and meso-porosity in a mono-modal distribution. The pore size distributions indicate smaller pores in the case of the co-precipitated sample. The preparation of films by co-precipitation and spray pyrolysis is shown to introduce a second region of meso-porosity. The deposition of co-precipitated powder as a film is investigated through the addition of a PTFE binder with and without a pressing step in the process. Porosity is shown to decrease through the addition of PTFE with no pressing and decrease further again when the film is subjected to pressing.

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