Accelerated Alcohol Oxidation on Platinum- and Rhodium-Modified Transition Metal Carbides and Nitrides

Direct alcohol fuel cells (DAFC’s) are promising sources of alternative energy: ethanol and methanol produce fewer emissions than fossil fuels, are readily portable, and have theoretical energy densities significantly greater than that of hydrogen. DAFC’s rely on the oxidation of either ethanol or methanol at their anodes, which pair with the oxygen reduction reaction at the cathode to produce electron flow. One major challenge faced by DAFC’s is the design of catalysts to improve sluggish alcohol oxidation rates while minimizing the amount of precious metal loading required. Transition metal carbides and nitrides (TMC’s and TMN’s, respectively) are a group of materials that can achieve similar activity to traditional catalysts when modified with metals such as platinum and rhodium, providing them enhanced structural support for improved reaction mechanisms.

This study uses eight different catalysts (NbN, NbC, TaN, and TaC modified with Pt and Rh) to improve the kinetics of ethanol and methanol oxidation. Chronopotentiometry was employed to ensure the stability of each catalyst over an hour in alkaline conditions, while cyclic voltammetry was used to explore different kinetic features of the catalysts. Through examining CV’s, the TMN’s and TMC’s almost uniformly achieved lower onset potentials for alcohol oxidation than baseline Pt/C and Rh/C, with Pt/NbN decreasing the ethanol oxidation onset potential by 0.176 V and Rh/NbC doing likewise for methanol oxidation by 0.407 V. Thus, a smaller thermodynamic energy threshold is required to achieve alcohol oxidation using these catalysts. When comparing TMN’s and TMC’s among each other, each catalyst shows the ability to perform alcohol oxidation to different degrees. Pt/TaC has by far the greatest catalytic activity for both ethanol and methanol oxidation as seen through CV peak areas, as well as smaller onset potentials than either baseline catalyst. This shows promise in accelerating alcohol oxidation kinetics while lowering the use of precious metals.