Molybdenum sulphides on carbon supports as electrocatalysts for hydrogen evolution in acidic industrial wastewater

•MoSx is an efficient and durable catalyst for H2 evolution in acidic wastewater.•MoSx outperformed Pt as H2-catalyst in long term in acidic wastewater.•Improved activity over time was likely due to changes in MoSx structure.

Microbial electrolysis cells (MECs) are an attractive future alternative technology to generate renewable hydrogen and simultaneously treat wastewaters. The thermodynamics of hydrogen evolution in MECs can be greatly improved by operating the cathode at acidic pH in combination with a neutral pH microbial anode. This can easily be achieved with acidic industrial wastewaters that have to be neutralised before discharge. For the hydrogen evolution reaction (HER) in acidic wastewater, efficient and inexpensive catalysts are required that are compatible with the often complex chemical composition of wastewaters. In this study, molybdenum sulphides (MoSx) on different carbon supports were successfully used for hydrogen evolution in different acidic media. At first, the cathodes were screened by linear sweep voltammetry in sulphuric acid (pH 0) or phosphate buffer (pH 2.2). After this, the overpotentials for H2 production of the best cathodes and their long term performances (⩾1 week) were determined in acidic industrial wastewater (pH 2.4) obtained from a plant mainly producing cellulose acetate. For the most promising MoSx cathodes, the overpotentials for HER (at 3 mA cm−2) were only ∼40 mV higher than for a platinum electrode. Most importantly, the catalytic efficiency of the MoSx electrodes improved in the wastewater over time (7-17 days), while Pt electrodes were found to be slowly deactivated. Thus, MoSx emerges as an affordable, efficient and especially durable electrocatalyst for HER in real acidic wastewaters and this could be an important contribution to take energy production from wastewaters in the form of hydrogen towards practical applications.