Self-reconstructed Co-B active sites for high-efficiency hydrolysis of ammonia borane

Low-cost and efficient catalysts are highly required for the hydrolysis of ammonia borane (AB) to conveniently produce H₂. Here, we have designed a CoO_x catalyst grown on an ErO_x nanosheet substrate (Co₉Er₁O_x) for the efficient hydrolysis of AB. Due to the favorable interfacial interaction between catalyst and substrate, the hybrid Co₉Er₁O_x catalyst shows a high total turnover frequency (TOF) value of 70.5 (H2) mol/(Cat-Co) mol·min with an activation energy of 48.5 kJ/mol, which is nearly 3 times higher than that of pure CoO_x catalyst. Moreover, by using in situ X-ray absorption spectroscopy (XAS) experiments, the self-reconstruction of Co during the hydrolysis process has been probed, which can transform the oxidized Co into a metallic Co particle as the real active site. Interestingly, a Co-B intermediate based on metallic Co has been first observed from the in situ XAS, strongly supporting the catalyst-AB interaction to facilitate the hydrolysis reaction.