The invention provides a nitrogen-functionalized platinum-transition metal catalyst having the formula Pt-M-NX/C (where M is a transition element such as Fe, Co, Ni, Nb, Ta, Ir, Rh, or Ru) for use at the hydrogen electrode of a hydrogen/bromine redox flow battery. The new catalyst possesses excellent activity and durability in the HBr/Br2 environment, showing superior resistance to halide poisoning than conventional Pt/C or Pt-M/C catalysts.