Metal nanoparticles deposited onto the surface of semiconductor light absorbers are widely used as catalysts for solar-driven fuel forming reactions, such as hydrogen evolution. The authors employ a suite of AFM techniques to investigate the interfacial properties of Pt/p-Si photocathodes prepared using electroless metal deposition, with several interesting findings.
Conductive AFM reveals that the majority of Pt/Si interfaces are highly resistive due to the existence of interfacial oxide. Local current-voltage spectra in air show rectifying behavior at the Pt/p-Si interface, which indicates that the conventional assumption of a Pt/p-Si ohmic contact in the inhomogeneous barrier height for photoelectrocatalysis might not be valid.
In addition, the deposited particles were mechanically well attached to the sample surface in air but not in liquid. To measure conductivity and local electrochemical activity in liquid at low forces, the authors employ PeakForce SECM and find that the resistive interface is the primary rate-limiting step for low performance of photoelectrodes prepared from electroless methods. This work is a great example of how AFM-based topographic, electrical, mechanical, and electrochemical measurements both ex situ in air and in situ during electrochemical reactions, can advance solar-fuels research.