Microbial fuel cells (MFCs) show large cathodic overpotentials for the O2 reduction reaction. The local cathode pH is important, as OH- ions accumulate on the catalyst surface, resulting in a Nernstian concentration overpotential. Herein, we explore how various relevant buffers affect cathode performance at neutral pH, by reducing the concentration overpotential. We show that NH4+ buffer results in the best performance at current densities >10Am-2, owing to buffering of the local pH close to its pKa (ca. 9.2). With other buffers, the local pH increases to >12 at similar current densities. We also show the importance of diffusion in buffer transport. Increasing the buffer concentration or improving the hydrodynamic conditions leads to lower overpotentials. We also present a mathematical model that includes buffer diffusion, for use in predicting cathode polarization curves. Overall, our results point to the promise of reducing cathode overpotentials in MFCs using naturally available buffers.

Original languageEnglish (US)
Pages (from-to)1909-1915
Number of pages7
Issue number11
StatePublished - Nov 1 2014


  • Ammonium
  • Buffer
  • Concentration overpotential
  • Neutral pH
  • Oxygen reduction reaction

ASJC Scopus subject areas

  • Catalysis
  • Electrochemistry


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