Benchmarking Faradaic Efficiency and O2 Quantification during Water Oxidation under Mild Conditions Using a 3D-Printed Cell and Clark Electrode

Abstract

Producing green hydrogen via water electrolysis offers a potential pathway for achieving a sustainable energy transition. Despite its potential, it is limited by the sluggish kinetics of OER, which motivates the development of efficient catalysts. In addition, the field still lacks standardized and reproducible approaches for evaluating catalyst faradaic efficiency (FE) and monitoring the oxygen production. Therefore, we present a 3D-printed electrochemical cell coupled with a Clark sensor for in situ oxygen quantification during OER, while measurement uncertainties were examined to confirm the precision and reproducibility of the methodology. The effects of electrolyte concentration (0.1, 0.5, and 1.0 mol L^–1 KNO₃), different electrolytes (KNO₃ and PBS), electrode surface area (0.071 and 0.195 cm²), and applied constant current (1, 5, and 10 mA) were investigated. Statistical validation demonstrated high reproducibility and robustness. At 10 mA in 0.1 mol L^–1 KNO₃ using a 0.071 cm² electrode area, Pt exhibited higher oxygen evolution and FE (4.55 ± 0.5 mg L^–1, 85.6 ± 10.8%) than GC (2.32 ± 0.3 mg L^–1, 43.6 ± 6.1%). The methodology was subsequently applied to Prussian blue (FePBA), and its respective cobalt and nickel Prussian blue analogues (CoPBA and NiPBA, respectively). Among the investigated materials, NiPBA exhibited the highest OER activity (0.40 ± 0.03 mg L^–1 with 76.5 ± 5.7% FE), and was comparable to CoPBA, while both outperformed FePBA at 1 mA. A trend in the NOP was observed among the PBAs, following the order NiPBA ≥ CoPBA > FePBA. This approach provides a reproducible platform for dissolved oxygen quantification and the standardized benchmarking of OER electrocatalysts.