Spinel cobalt nanostructures: Impact of calcination temperature on structural, microstructural, optical, magnetic, and photo/electro catalytic traits towards HER

Cobalt ferrite (CoFe₂O₄) based catalysts are known to have the excellent catalytic traits due to their usefulness as a photocatalyst and electrocatalyst for the hydrolysis of water in the field of sustainable growth. This research work is reported to understand the impact of calcination temperature on the photo and electro catalytic nature of CoFe₂O₄ ferrites for the green H₂ generation. The CoFe₂O₄ ferrite has been fabricated using the sol-gel auto-combustion (SG) approach at different calcination temperatures (650°C, 750°C). According to the Rietveld refined XRD data, all samples showed the formation of Fd3m geometry representing the spinel phase with crystallite size increasing from 30.65 to 46.01 nm. The morphological studies revealed the existence of aggregates. The size of the aggregates with spherical morphology changes with the calcination temperature going from 46.78 nm to 92.55 nm. The VSM analysis indicates the ferromagnetic behavior of fabricated cobalt ferrites with the rise in saturation magnetization. The optical band analysis showed systematic band reduction to 1.45 eV from 1.72 eV. Moreover, it was observed that the inclining temperature causes increase in the inverse type of the cobalt ferrite, which benefits the catalytic processes. The water splitting studies demonstrated that the samples calcined at 750°C have high catalytic activity for both photo and electrocatalysis processes. The highest achieved H₂ yield is of 27.99 mmol g_cat⁻¹ in 8 hours by the CF3 sample with the lowermost achieved Tafel slope of 106.22 mV/dec. Therefore, the current work shows that the cobalt ferrites have un-tapped potential in the field of H₂ energy production.