Catalysts SPECM Water Splitting

Micropatterning of a photocatalyst surface followed by evaluation of its local catalytic activity

The ElProScan ELP 3 SPECM has been used for an innovative two-step scanning photoelectrochemical microscopy (SPECM) experiment consisting of micropattering and consecutive evaluation of catalytic activty.

In the first step, a BiVO4 seminconductor surface was modified by photodeposition with the electrocatalyst FeOOH to fabricate a photocatalyst system for the photoelectrochemical water splitting reaction. The inverted microscope of the ELP 3 was hereby used to illuminate different spots of the surface with varying illumination time (10, 15, 20 and 25 min) in a matrix scan. This way, a regular pattern with catalytically active spots with different loadings of FeOOH were produced.

In the second step, the photocatalyst pattern was scanned via SPECM and the photocurrent at the sample was recorded yielding a map showing that the highest catalytic activity is found for the spot after 20 min of photodeposition. Additionally, to determine the Faradayic efficiency the oxygen which was produced in the water splitting reaction was detected by the oxygen reduction reaction (ORR) at a microelectrode . The microelectrode was aligned with inverse microscope and therefore with the illuminated sample area. Shear Force Sensing was used to keep a constant distance between microelectrode and sample surface to probe the pure catalytic activity without effects of sample topography. The z position of the microelectrode is further used to obtain the topography map of the sample.

Photodeposition of FeOOH catalyst spots with different loading on a BiVO4 semiconductor surface by SPECM (left) and consecutive evaluation of their catalytic activity by SPECM (right). The recorded signals are the photocurrent at the sample, the locally produced oxygen at the microelectrode and the topography via Shear Force Sensing.

Chen, S., Prins, S. and Chen, A. (2020) ‘Patterning of BiVO4 Surfaces and Monitoring of Localized Catalytic Activity using Scanning Photoelectrochemical Microscopy’, ACS Applied Materials & Interfaces.

These experiments show that the multi-functional ELP 3 SPECM can be used to easily fabricate catalyst libraries which can in a second step be evaluated regarding their local catalytic activity greatly accelerating the search for new highly active catalyst materials.

The latest model of our ELP 3 SPECM-FL has a second illumination port for small spot illumination for illuminated spot sizes down to 5 µm. This match of illuminated sample area and microelectrode size further improves the collection efficiency at the microelectrode and the quality of the experimental results.