# Structural and Electrocatalytic Studies of Pulsed Laser Deposited Epitaxial RuO2 Thin Films

## TL;DR

Thicker RuO2 films made with pulsed laser deposition show better electrocatalytic performance due to lower electrical resistance.

## Contribution

Demonstrates that thicker RuO2 films on sapphire substrates achieve superior electrocatalytic properties.

## Key findings

- Thicker RuO2 films (87 nm) have lower sheet resistance (6.7 Ω/□) compared to thinner films (40 nm, 15.7 Ω/□).
- Thicker films exhibit lower overpotential (280 mV) for oxygen evolution compared to thinner films (320 mV).
- Lower electrical resistance in thicker films enhances charge transfer and electrocatalytic performance.

## Abstract

Two sets of high-quality epitaxial ruthenium oxide (RuO2) thin films with different thicknesses were synthesized in
situ
on cost-competitive sapphire substrates by using a pulsed laser deposition
technique. The first set of films, with a thickness of 40 nm and a
sheet resistance of 15.7 Ω/□, was prepared using 2100
laser pulses, while the second set of films, with a thickness of 87
nm and a sheet resistance of 6.7 Ω/□, was prepared using
4800 laser pulses. All other deposition parameters were kept the same.
The post-deposition structural and morphological measurements showed
that both sets of films grew at the same growth rate, had the same
crystallinity, similar grain boundary density, and slightly different
surface roughness. The thicker RuO2 films achieved an overpotential
of 280 mV for the oxygen evolution reaction at a current density of
100 μA/cm2, comparable to or exceeding the performance
of films grown on more expensive substrates. Comparatively, the thinner
RuO2 films, which have a significantly higher charge transfer
resistance (250 Ω versus 100 Ω for thick films), display
a higher overpotential of 320 mV. These results indicate that the
lower electrical resistance of thicker films promotes charge transfer
through the film body, leading to superior electrocatalytic properties.