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Ferrite MFe2O4 (M = Ni, Co, etc.) metal oxides have been the focus of intense research, studied as promising electrocatalysts due to their good catalytic activity and stability for oxygen evolution reaction (OER). Structure engineering is a significant solution to achieve a high catalytic performance; further, optimizing the structure and specific surface area (SSA) of metal ferrite (CoFe2O4 and NiFe2O4) is regarded as a good choice. Herein, we designed hierarchical porous nanostructured CoFe2O4 and NiFe2O4 microspheres with the assistance of sodium dodecyl sulfonate by solvothermal and annealing methods. We found that three-dimensional microspheres assembled by nanoparticles and porous nanosheets exhibit higher SSAs for NiFe2O4 (158.47 m2 g–1) and CoFe2O4 (144.52 m2 g–1). Their higher SSA is much higher than those of other CoFe2O4-based and NiFe2O4-based materials. The as-prepared metal ferrite microspheres exhibit excellent OER electrocatalytic activity with lower Tafel slopes (55.2 and 58.2 mV dec–1) and lower overpotentials (235 and 280 mV) at a constant current density of 10 mA cm–2 and long-term stability, which is better than that of NiFe2O4 and CoFe2O4 bulks. This method for preparing a large SSA is expected to be applied in other spinel metal oxides.

Piezo-photocatalytic technique is a new-emerging strategy to alleviate photoinduced charge recombination and thus enhance catalytic performance. The heterojunction construction engineering is a powerful approach to improve photocatalytic performance. Herein, the BiOCl/NaNbO3 with different molar ratios piezoelectric composites were successfully synthesized by hydrothermal methods. The piezo/photodegradation rate (k value) of Rhodamine B (RhB) for BiOCl/NaNbO3 (BN-3, 0.0192 min−1) is 2.2 and 5.2 times higher than that of BiOCl (0.0089 min−1) and NaNbO3 (0.0037 min−1), respectively. The enhanced performance of BN-3 composite can be attributed to the heterojunction construction between BiOCl and NaNbO3. In addition, the piezo/photodecomposition ratio of RhB for BN-3 (87.4%) is 8.8 and 2.2 times higher than that of piezocatalysis (9.9%) and photocatalysis (40.4%), respectively. We further investigated the mechanism of piezocatalysis, photocatalysis, and their synergy effect of BN-3 composite. This study favors an in-depth understanding of piezo-photocatalysis, providing a new strategy to improve the environmental pollutant remediation efficiency of piezoelectric composites.

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