A niobium nitride diffusion layer (Nb-N layer) has been synthesized via the plasma surface diffusion alloying (PSDA) technique on the surface of AISI316L stainless steel (316L SS), which is used as bipolar plates of direct formic acid fuel cells (DFAFCs). The niobium nitride-modified AISI316L stainless steel (Nb-N 316L SS) has a compact and successive niobium nitride diffusion layer with a single cubic NbN phase. The corrosion resistance and surface conductivity of Nb-N 316L SS are systematically investigated in the simulated anodic environments of DFAFC (0.05 M H2SO4 +2 ppm HF + x M formic acid (x = 2, 5, 10 and 15) at 50 degrees C). The potentiodynamic and potentiostatic polarization tests demonstrate that the corrosion resistance of 316L SS is distinctly ameliorated in the simulated DFAFC environments after the PSDA modification. The interfacial contact resistances (ICR) of Nb-N 316L SS are much smaller than those of bare 316L SS before and after potentiostatic polarization tests. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.