Due to the precisely controllable size, shape and composition, self-assembled nanocrystal superlattices exhibit unique collective properties and find wide applications in catalysis and energy conversion. Identifying their intrinsic electrocatalytic activity is challenging, as their averaged properties on ensembles can hardly be dissected from binders or additives. We here report the direct measurement of oxygen evolution reaction at single superparticles self-assembled from ~8 nm NiFe2O4 and/or ~4 nm Au nanocrystals using the scanning electrochemical cell microscopy. Combined with coordinated scanning electron microscopy, it is found that the turnover frequency (TOF) estimated from single NiFe2O4 superparticles at 1.92 V vs. RHE ranges from 0.2 to 11 s-1 and is sensitive to size only when smaller than ~800 nm in diameter. After the incorporation of Au nanocrystals, the TOF increases by ~6-fold and levels off with further increasing Au content. We also investigate the effect of nanocrystal ordering and disordering within the nanocrystal superparticles. Our study demonstrates the first direct single entity electrochemical study on individual nanocrystal superlattices with tunable structures and unravels the intrinsic structure-activity relationship that is not accessible by other methods.

Direct probing of the oxygen evolution reaction at single NiFe2O4 nanocrystal superparticles

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.