Automated Electrodeposition of Co-Pi onto Hematite Photoanodes Using a Scanning Flow Cell

BENAVENTE LLORENTE, VICTORIA; JOANNA PRZYBYSZ; MARKUS BIERLING; KEN J. JENEWEIN; ATTILA KORMÁNYOS; SIMON THIELE; SERHIY CHEREVKO

Congreso; 34th Topical Meeting of the ISE; 2023

Photoelectrochemical (PEC) water splitting is a promising energy conversion approach that harvests sunlight to produce hydrogen. Out of the most promising oxides, Fe2O3 has been extensively studied as a metal oxide photoanode to drive the oxygen evolution reaction (OER) due to its narrow band gap (1.9-2.2 eV), appropriate conduction band alignment for water oxidation, low-cost, and high abundance. Nevertheless, Fe2O3 has inherent disadvantages, such as slow charge-transfer kinetics to oxidize water [1]. The slow kinetics can be overcome by electrodepositing (EDP) a co-catalyst for OER, such as mixed non-noble metal oxides or phosphates [2,3]. However, finding the optimal EDP conditions can be time-consuming. Therefore, the use of accelerated EDP under different protocols to rapidly evaluate the best conditions is of great importance.This work focuses on the automated photo-assisted electrodeposition (PAED) of cobalt phosphate (Co-Pi) on Fe2O3 photoanodes. Fe2O3 photoanodes of 25 cm2 are prepared using the hydrothermal method and used as a model platform to deposit different thicknesses of Co-Pi. For this purpose, we used a photoelectrochemical scanning flow cell (PEC-SFC). As reported recently, the PEC-SFC can be programmed to automatically perform a specific electrochemical protocol in selected coordinates of the working electrode [4]. Using this automated process, a grid of spots differing in their deposition protocol (current, time, etc.) can be fabricated to reveal their effect on the Co-Pi thickness. Fig.1 a) Scheme of the PEC-SFC used to perform the automated PAED of Co-Pi. b) Schematic description of the PAED of Co-Pi onto Fe2O3 c) Photo of Co-Pi spots deposited onto Fe2O3 using the PEC-SFC at different times applying 0.4 V vs. Ag|AgCl (Electrolyte 0.5 mM Co(II) solution in 0.1 M phosphate buffer at pH=7.0).The electrolyte flows through the cell, contacting a selected spot (See Figure 1a), to provide Co(II) ions that react with the photogenerated holes from the valence band to deposit Co-Pi anodically (See Figure 1b). Preliminary measurements have demonstrated that the PAED of Co-Pi was successful in a defined grid (See Figure 1c). The automated approach explored in this work opens opportunities to accelerate the optimization of EDP conditions for different co-catalysts onto photoanode materials. Exploring surface-modified photoanodes might guide the design of more active photoanodes for PEC solar-to-fuel production.