Sub-particle reaction and photocurrent mapping to optimize catalyst-modified photoanodes

Using single-molecule fluorescence imaging of photoelectrocatalysis, the charge-carrier activities on single TiO 2 nanorods and the corresponding water-oxidation photocurrent are mapped at high spatiotemporal resolution, revealing the best catalytic sites and the most effective sites for depositing an oxygen evolution catalyst. Better photoelectrochemical water splitting The photoelectrochemical cleavage of water into hydrogen and oxygen is a promising solar-to-fuel energy conversion technology. Attempts to make the process more efficient usually require the photoanodes to be modified with an oxygen evolution catalyst, but little information is available to inform this process. Justin Sambur et al . use in operando imaging, with unprecedented resolution, to map the photoelectrocatalytic activities on single TiO 2 nanorods. The data show which photoanode sites are active, and reveal which catalyst deposition sites enhance or worsen performance and why. The methods used are applicable to a wide range of material systems, and should enable the rational, activity-based development of improved catalyst-modified photoelectrodes for solar energy conversion. The splitting of water photoelectrochemically into hydrogen and oxygen represents a promising technology for converting solar energy to fuel 1 , 2 . The main challenge is to ensure that photogenerated holes efficiently oxidize water, which generally requires modification of the photoanode with an oxygen evolution catalyst (OEC) to increase the photocurrent and reduce the onset potential 3 . However, because excess OEC material can hinder light absorption and decrease photoanode performance 4 , its deposition needs to be carefully controlled—yet it is unclear which semiconductor surface sites give optimal improvement if targeted for OEC deposition, and whether sites catalysing water oxidation also contribute to competing charge-carrier recombination with photogenerated electrons 5 . Surface heterogeneity 6 exacerbates these uncertainties, especially for nanostructured photoanodes benefiting from small charge-carrier transport distances 1 , 7 , 8 . Here we use super-resolution imaging 9 , 10 , 11 , 12 , 13 , operated in a charge-carrier-selective manner and with a spatiotemporal resolution of approximately 30 nanometres and 15 milliseconds, to map both the electron- and hole-driven photoelectrocatalytic activities on single titanium oxide nanorods. We then map, with sub-particle resolution (about 390 nanometres)