P-067

Ramūnas Levinas

ramunas.levinas@ftmc.lt

Ina Stankevičienė, Aldona Jagminienė, Vidas Pakštas, Tomas Murauskas, Giedrius Stalnionis, Loreta Tamašauskaitė-Tamašiūnaitė

Center for Physical Sciences and Technology (FTMC), Lithuania

Tailoring ultralow loading Rh@TiO₂/Cu Composite Electrodes for Superior PEC and HER Performance

Efficient utilization of renewable energy is one of the key pillars of establishing a robust energy grid worldwide. Electrocatalytic water splitting is a widely known way to obtain green hydrogen, while photoelectrochemical (PEC) devices are systems that use light to convert reactants into products with higher chemical energy. Such devices should exhibit good efficiency, stability, and functionality. Although new materials for these applications are actively being researched, an alternative strategy is to use tested and efficient (but often expensive) materials, but in ultralow quantities.

To this end, in this study TiO₂ films were synthesized by a technique called plasma electrolytic oxidation (PEO), resulting in ~ 1 µm thick films with large diameter channels. Cu was then electrochemically deposited into these channels from an optimized electrolyte, and the level of filling was adjusted by limiting the amount of charge passed (0.5 C to 1.5 C). Lastly, galvanic displacement of surface Cu by Rh was carried out at 40 °C to deposit an ultralow amount of Rh catalyst, which yielded composite Rh@TiO₂/Cu electrodes. XRD characterization confirmed that the dominant TiO₂ phase was anatase, and a strong signal of metallic Cu was observed. Up to 0.73 % of Rh was detected by EDX, while XPS revealed a mixture of Rh⁰ (62.7%) and Rh³⁺ (37.3%) valence states, confirming successful galvanic displacement and formation of metallic Rh and Rh₂O₃. 

The films were characterized as photoanodes for PEC OER, and as electrocatalytic cathodes for HER in 1 M KOH. They showed good photoactivity with 365 nm illumination, owing to the anatase TiO₂, and would generate photocurrents of up to 0.17 mA cm⁻² at 1.23 V vs RHE (2.31% IPCE at 365 nm, 25 mW cm⁻²), but lower photocurrents were obtained with higher Cu filling. The same films performed very well as HER electrocatalysts (due to Rh), reaching 10 mA cm⁻² at an overpotential of 58 mV, with a Tafel slope of 40 mV dec⁻¹. Electrochemical impedance spectroscopy (EIS) was used to investigate the double layer capacitance and charge transfer kinetics for HER. It was determined that, despite the apparent small amount of Cu and Rh being deposited, the electrochemically active surface area is very large (Cdl on the order of mF cm⁻²). Therefore, this study demonstrates the relatively simple synthesis and photo-/electrocatalytic versatility of multi-functional composite Rh@TiO₂/Cu films.