Renewable energy such as wind and solar has grown exponentially resulting in a high demand for low-cost, modular and scalable energy storage. Redox Flow Batteries (RFBs) offer improved flexibility in energy capacity and power density for grid-scale energy as compared to NaS & Li-ion batteries which are currently in-use. In particular, H₂-Br₂ RFBs are known for their low-cost components such as electrolyte (HBr) and electrodes (Br-/Br₂). However, the hydrogen electrode of H₂-Br₂ flow cells suffers from well-known stability issues as a result of halide adsorption on the catalyst surface and Pt dissolution. The shortcomings occur due to Br₂ cross-over. Finding a catalyst that could overcome this would be a significant milestone in addressing energy needs. Northeastern University Center for Renewable Energy Technology (NUCRET) synthesized and tested several Pt & Ir nitride catalyst. These catalyst materials were screened for hydrogen evolution reaction and hydrogen oxidation reaction (HER-HOR) activity via a rotating disk electrode (RDE) cell. RDE studies of pure Ir/C and Pt/C catalysts showed that the Ir-component and Pt- component are active for both HER & HOR. However, Ir or Pt catalysts alone are not stable under stability testing conditions which involve high-voltage cycling or exposure to Br₂.  NUCRET successfully synthesized 40 wt% Pt-Ir-N_x/C sample that exhibited i₀ well above the 0.6 A/ mg target.  This Pt-Ir-N_x/C catalyst, along with commercial Pt-Ir/C and Pt/C, were also subjected to stability testing in 1M HBr with 1mM Br₂ The Pt-Ir-N/C sample exhibited increased stability compared to the commercial Pt-Ir/C and Pt/C catalysts. Cyclic Voltammetry (CV) results suggest that the Pt-Ir-N_x/C sample suffered ~50% loss in HER/HOR activity (Figure 1 right). In addition, Pt-Ir-N_x/C sample lost about 30% of electrochemical active surface area (ECSA) (Figure 1 left), compared to 70% Pt-Ir/C and 100% Pt/C standard loss.  This presentation will attempt to analyze the results from the point of view of the effect of nitrogen functionalization as distinct from other factors such as particle size, etc.  Use of in situ synchrotron XAS spectroscopy and Raman in conjunction with electrochemical data both from single cell as well as RDE will be presented.  

Acknowledgement