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The vanadium redox flow battery mainly consists of an electrode, membrane, and electrolyte. Positive and negative electrodes have great importance to the battery's performance. Electrodes were treated thermally, acid and plasma and modified with carbon-based and metal-based electrocatalysts to increase their electrochemical activity, active area, stability, and functional groups. In this study, comprehensive research was conducted on carbon-based and metal-based electrocatalysts. Furthermore, modification and treatment methods, chargedischarge potential, maximum capacity, capacity fading, and energy efficiency of the electrode were examined at the same current density. The highest energy efficiency of the carbon-based electrocatalyst was obtained for graphite felt doped with carbon nanoparticles. The energy efficiency of bare graphite felt was 67.4%, the efficiency increased up to 84.8% with the carbon nanoparticle electrocatalyst.Ohmic loss was reduced, and operating voltage window was enlarged. For metal electrocatalysts, the highest energy efficiency was obtained by titanium nitride modification. The energy efficiency increased from 68% to 89% in comparison to the bare electrode. Electrode kinetics and reversibility were improved by electrocatalyst doping, and the active area of the electrode was increased.

This study aimed to investigate the effects of the operating conditions on the anisotropic electrical conductivity of diffusion layers in a polymer electrolyte membrane fuel cell. For this purpose, two different gas diffusion layers were considered. The electrical conductivity values of the selected gas diffusion layers in both in-plane and through-plane directions were examined experimentally, depending on cell temperature, relative humidity and clamping pressure. Resistance measurements were carried out for all combinations of operating conditions where cell temperature, relative humidity (RH) and clamping pressure were changed from 50°C to 80°C, from 70% to 100% and from 2 bars to 8 bars, respectively. The results showed that although the relative humidity had a dominant effect on the in-plane conductivities for both the gas diffusion layers, it did not significantly affect the through-plane conductivities. The through-plane conductivities increased with the increase of the cell temperature and the clamping pressure, whereas the in-plane conductivities did not remarkable change.

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