Virus-directed formation of electrocatalytically active nanoparticle-based Co₃O₄ tubes

Spinel-type Co₃O₄ finds applications in a wide range of fields, including clean energy conversion, where nanostructured Co₃O₄ may provide a cost-efficient alternative to platinum- and iridium-based catalysts for electrocatalytic water-splitting. We here describe a novel strategy in which basic cobalt carbonate - a precursor to Co₃O₄ - is precipitated as sheet-like structures and microspheres covered with fine surface protrusions, via ammonium carbonate decomposition at room temperature. Importantly, these mild reaction conditions enable us to employ bio-inspired templating approaches to further control the mineral structure. Rod-like tobacco mosaic viruses (TMV) were used as biotemplates for mineral deposition, where we profit from the ability of Co(ii) ions to mediate the ordered assembly of the virus nanorods to create complex tubular superstructures of TMV/ basic cobalt carbonate. Calcination of these tubules is then achieved with retention of the gross morphology, and generates a hierarchically-structured solid comprising interconnected Co₃O₄ nanoparticles. Evaluation of these Co₃O₄ materials as electrocatalysts for the oxygen evolution reaction (OER) demonstrates that the activity of Co₃O₄ prepared by calcination of ammonia diffusion-grown precursors in both, the absence or presence of TMV exceeds that of a commercial nanopowder.