Bulk gold (Au) and other non-Pt metals
have attracted little attention in electrocatalysis
toward ORR due to their poor catalytic
performance that is confirmed by both
experimental evidence and density functional
theory (DFT) calculations.3,10 Fortunately,
recent studies have demonstrated
that the Au particles with the sizes of less
than 2 nm, which are also known as clusters
differentiating from nanoparticles (NPs)
due to their small sizes and narrow size
distribution,11 have much higher electrocatalytic
activity for ORR than the bulk Au and
larger Au NPs.12,13 The enhanced catalytic
activity of Au clusters is accounted for by the
high fraction of low-coordinated surface
atoms and that oxygen molecules can be
adsorbed on the cluster surface and activated
more easily than the close-packed counterparts.
1217 The utilization of the clusters as the
electrocatalysts will not only dramatically improve
the efficiency of ORR but also considerably
decrease the materials cost