Tetramethylguanidine as an Aqueous Alkaline Electrolyte for Electrochemical Devices with Pt and Pd

1,1,3,3-Tetramethylguanidine (TMG) is an organic superbase which has recently found use as a primary functional group in alkaline anion exchange membranes (AAEM). In this study we demonstrate the potential of aqueous TMG alkaline electrolyte as a substitute for NaOH(aq)/KOH(aq) with greater chemical similarity to AAEM functional groups. The water redox activities of Pt and Pd electrodes in 0.1 M TMG and 0.1 M KOH are compared, while hydrogen evolution/oxidation reactions (HER/HOR) and the oxygen reduction reaction (ORR) are studied in depth. Aqueous TMG supports comparable redox activity to KOH of equal concentration, but modifies surface processes through potential-dependent adsorptive behaviors. Rotating electrode, capacitance, and slow polarization measurements suggest that TMG and its decomposition species delay and participate in HER. HOR on Pt resembles that of a perfectly flat (111) surface in KOH, while hydrogen absorption on Pd is significantly hindered. ORR activity is dependent upon overpotential on both electrodes. But unlike most acid and alkaline electrolytes, TMG appears to alter the reaction pathway on Pt toward a 1.5e– route. We propose that native or modified analogues of TMG might be optimized for compatibility with various catalysts so as to be utilized in alkaline electrochemical devices in place of NaOH and KOH.