Transport through Carbon electrodes and New Catalysts for an Organic-Air Hybrid Redox Flow Battery

Incorporation of different energy-harnessing technologies creating a renewable energy network is important for providing safe and reliable power to those connected. To date, the most promising and effective technologies used to harness renewable energy sources are solar photovoltaic arrays (PV) and wind farms. The intermittent nature of these sources of energy is a problem but can be managed with the use of large-scale energy storage devices. Redox Flow Batteries (RFBs) are a relatively nascent technology which would allow longer term energy storage to the grid for a lower price.
Symmetric single-electrolyte flow cell testing is used to compare carbon paper / cloth electrodes with different microstructural properties. Polarisation and impedance spectroscopy data are obtained and used to determine the performance of the system as a function of electrolyte viscosity and flow rate and heat treatments of electrodes. Ex-situ X-ray tomographic data of compressed electrodes is gathered to highlight how microstructural parameters might help to explain overall performance of the cell.
This project aims to develop a full organic air RFB system. While the above methods help us to understand the processes happening in the anode component (organic side) of the RFB, the cathode (air side) requires more work. In developing an 'air electrode,' an effective bifunctional electrocatalyst that allows both the oxygen reduction and evolution reactions (ORR/ORR) to happen must first be developed and subsequently appended to a carbon (/other conductive material) support.
Creation of an air-breathing electrode would dramatically increase the power density and reduce the associated costs for RFB operation. The second part of this work seeks to develop an electrocatalyst that will ultimately be used in the cathode of this organic-air hybrid RFB. Using simple LSV / CV scans for ORR and OER as indicators, the synthesis route of the catalyst is optimised, and the catalyst is shown to be resistant at different pHs, unlike many electrocatalysts that are only effective at specific pHs. The carbon substrate, ZIF-67's size and overall morphology influences the performance. The synthesis route ensures a lower loading of iridium is transmetallated into the catalyst and therefore the mass activities are much higher than with commercial OER materials. For the best performing material, E is 724 mV, which is competitive with state-of-the-art bifunctional catalysts.