Electrochemical evaluation of molybdenum disulfide as a catalyst for hydrogen evolution in microbial electrolysis cells

There is great interest in hydrogen evolution in bioelectrochemical systems, such as microbial electrolysis cells (MECs), but these systems require non-optimal near-neutral pH conditions and the use of low-cost, non-precious metal catalysts. Here we show that molybdenum disulfide (MoS2) composite cathodes have electrochemical performance superior to stainless steel (SS) (currently the most promising low-cost, non-precious metal MEC catalyst) or Pt-based cathodes in phosphate or perchlorate electrolytes, yet they cost ∼4.5 times less than Pt-based composite cathodes. At current densities typical of many MECs (2–5 A/m2), the optimal surface density with MoS2 particles on carbon cloth was 25 g/m2, achieving 31 mV less hydrogen evolution overpotential than similarly constructed Pt cathodes in galvanostatic tests with a phosphate buffer. At higher current densities (8–10 A/m2) the MoS2 catalyst had 82 mV less hydrogen evolution overpotential than the Pt-based catalyst. MoS2 composite cathodes performed similarly to Pt cathodes in terms of current densities, hydrogen production rates and COD removal over several batch cycles in MEC reactors. These results show that MoS2 can be used to substantially reduce the cost of cathodes used in MECs for hydrogen gas production.