Exploring Facile Oxygen Evolution Reaction One-Dimensional Catalyst Synthesis Using K2IrCl6
Authors: Brochoire Alexandra , Hou Dehua , Du Shangfeng 
Published: December 2024

Proton Exchange Membrane (PEM) water electrolysers are one of the most promising technologies for easy production of zero-carbon green hydrogen.

The global demands for decarbonised means of production have pushed for greater development of this technology. However, PEM water electrolysers reach an efficiency limit most notably due to the sluggish kinetics of the Oxygen Evolution Reaction (OER) happening at their anodes. This is heavily due to the four electron transfer steps creating a consequential energetic barrier.

As such, there is significant interest in improving OER catalysts to achieve optimal performance. This entails minimising rare metal usage to meet current sustainability ambitions. Modifying catalytic structures and creating nanoshapes to reduce the metal loading is a popular method to achieve this goal.

In our work, we provide a novel facile method to synthesise nanocatalysts with evidence of predicted better performance than commercial OER catalysts.

Previous work conducted by the group focused on using a K2PtCl6 precursor to develop one-dimensional Hydrogen Evolution Reaction (HER) catalysts.

Inspired by this, K2IrCl6 is used as a precursor and via a facile wet chemistry method iridium nanomaterials are obtained. The main process involves adding formic acid as the reducing agent and water solvent and letting the reaction occur in a stainless-steel autoclave at the desired temperature.

The advantages of this reaction include the accessibility of the reagents and the facile extraction method that does not require centrifuging. Other attempted wet methods presented in literature were subject to consequent product losses due to strong electrostatic interactions between the iridium particles and the plastic centrifuging vessels.

The focus of the experimental work is to investigate the effects of temperature, time of reaction, and quantity of reducing agent on the performance of the resulting catalysts. This was done by altering the parameters of an existing internal protocol.

Electrochemical performance is measured via Linear Sweep Voltammetry, and specifically looking at the overpotential at 10 mA.cm2. Voltammetry tests were performed in a 0.1M perchloric acid electrolyte, purged with nitrogen for 40 minutes before each measurement. Iridium black was used as a reference commercial catalyst, giving an overpotential of 358 mV at 10 mA.cm-2.

Current results indicate that higher performance is achieved by doubling the amount of formic acid compared to the initial protocol (1.08 mL vs 0.54 mL). A difference of up to 50 mV in overpotential was observed, suggesting that further investigation on the optimal quantity of reducing agent to be added might be of interest. Improved results were also obtained by letting the reaction run for 24 hours compared to the initial setting of 14 hours.

TEM images will be obtained for each sample in order to make two correlations: one between the synthesis conditions and the structure of the catalyst, and the main one between the structure and the performance of each material. The goal of this comparison will be to determine if one-dimensionality leads to the best OER performances in our catalyst. Furthermore, the catalysts will be put through single-cell tests to observe whether the performance trends observed with Linear Sweep Voltammetry hold when the catalysts are put in practical application settings. Further work will include combining the optimal catalyst with a support to further reduce iridium loading.

Figure 1