The widespread use of metal-air batteries for mobile applications will require reduced Pt loading and enhanced catalytic activity within their cathodes to drive the sluggish oxygen reduction reaction (ORR). Despite tremendous efforts, however, elegant bottom-up synthesis of practical nanomaterials remains highly challenging. Here, we propose “in-situ observation” as a novel descriptor to nicely bridge the adsorbates coverage and the oxygen reduction activity of Pt-based catalysts. In-situ X-ray powder diffraction characterization directly observed the ORR process and the evident change of the (111) peak intensity shows continuous oxygen adsorption on the catalyst surface. As expected, the catalyst exhibiting the greatest intensity change delivers the best oxygen reduction activity with a half-wave potential of 0.92 V versus reversible hydrogen electrode and an excellent bifunctional performance with a small potential difference of 0.75 V. Once assembled as the cathode catalyst, both aqueous and all-solid-state zinc-air battery illustrate high power density and superior cycling stability, holding great potential as a novel energy supply for wearable electronics. The cutting-edge in-situ observation is thus identified as a valid activity descriptor to guide less empirical synthesis of enhanced ORR electrocatalysts.
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