Scanning electrochemical probe microscopy: towards the characterization of micro-and nanostructured photocatalytic materials

Platinum-black (Pt-B) has been demonstrated as an excellent electrocatalytic material for the electrochemical oxidation of hydrogen peroxide (H2O2). As Pt-B films can be deposited electrochemically, micro- and nano-sized conductive transducers can be modified with Pt-B. Here, we present the potential of Pt-B micro- and sub-micro-sized sensors for the detection and quantification of hydrogen (H2) in solution. Using these microsensors, no sampling step for H2 determination is required and e.g., in photocatalysis, the onset of H2 evolution can be monitored in situ. We present Pt-B- based H2 micro- and sub-micro-sized sensors based on different electrochemical transducers such as microelectrodes and atomic force microscopy (AFM)- scanning electrochemical microscopy (SECM) probes, which enable local measurements e.g., at heterogenized photocatalytically active samples. The microsensors are characterized in terms of limits of detection (LOD), which ranges from 4.0 µM to 30 µM depending on the size of the sensors and the experimental conditions such as type of electrolyte and pH. The sensors were tested for the in situ H2 evolution by light-driven water-splitting, i.e., using ascorbic acid or triethanolamine, showing a wide linear concertation range, good reproducibility, and high sensitivity. Proof-of-principle experiments using Pt-B-modified cantilever-based sensors were performed using a model sample like platinum substrate to map the electrochemical H2 evolution along with the topography using AFM-SECM.