Transformation of Co(OH)

The development of efficient and economical oxygen evolution reaction (OER) catalysts is highly desired, and cobalt-based nanomaterials are promising candidates. In this work, we tackle one key question for cobalt-assisted photocatalytic OER: What is the true active species of Co(OH)2 for the photocatalytic OER? Hence, we investigated photocatalytic OER on nanostructured Co(OH)2 and Co3O4 for comparison. We found that there was a significant transformation of Co(OH)2 during the photocatalytic process with a [Ru(bpy)3]2+/S2O82- buffer. Specifically, the Co(OH)2 nanosheets were oxidized and mainly converted to CoOOH nanoparticles, one type of highly active material for the OER. The converted CoOOH exhibits higher photocatalytic OER performance than Co3O4 nanoparticles. CoOOH is the true active catalyst for the photocatalytic OER on Co(OH)2. Furthermore, potential-determining steps calculated by theoretical calculations also indicate that Co(OH)2 is unlikely to be the catalyst for the OER, and CoOOH exhibits better OER activity than Co3O4.