Cathode catalysts in polymer electrolyte membrane fuel cells (PEMFCs) are often supported by carbon, which is susceptible to corrosion at operating potentials. Transition metal carbides (TMCs) are a class of material that could be used as catalyst supports to replace carbon as they are electrically conductive and can be resistant to corrosion. TMCs which show promising activity for the oxygen reduction reaction (ORR) have been shown to suffer from oxidation and dissolution, whereas corrosion-resistant carbides tend to have significantly lower ORR activities. Here we used co-reduction carburization to synthesized alloys of Mo2C and TaC with the aim of designing a carbide support that was both active and corrosion resistant. The addition of 15 mol% Ta to the precursor mixture used to synthesize the alloy support increased the corrosion potential by nearly 150 mV and decreased the corrosion current to 16% of that observed in the Ta-free support. While Ta-alloyed Mo2C supports had reduced ORR activity compared to their Ta-free counterparts, the Ta-alloyed supports performed favorably when compared to Vulcan XC-72. We show that further improvements to alloy-carbide based supports can be achieved by modulating the structure of the catalyst particles from Pt to Pt3Ni. Furthermore, density functional theory (DFT) calculations can be used to predict oxygen binding and corrosion resistance in digitally designed alloy carbides. (C) 2019 The Electrochemical Society.