Efficient hydrogen recovery with CoP-NF as cathode in microbial electrolysis cells

The emerging microbial electrolysis cell (MEC) is of great potential for energy recovery from wastewater as hydrogen, while the application of MECs required cost-effective, scalable cathodes. Here, the phosphating cobalt (CoP) acicular nanoarray in-situ growing on a 3D commercial nickel foam (NF) matrix without binder demonstrated outstanding electrocatalytic activity. The nano-CoP coated NF (CoP-NF) was assessed for hydrogen recovery performance in MEC. In electrochemical testing, the CoP-NF demonstrated comparable performance to a commercial Pt/C catalyst in linear scan voltammetry tests. The lower Tafel slope of 175.4 mV dec−1 in 1 M phosphate buffer electrolyte indicated more favorable electrochemical kinetics of CoP-NF than commercial Pt/C. The CoP-NF demonstrated higher electrochemical active surface area of electrode-liquid interface for its acicular nano-structure, while the smaller charge transfer resistance of CoP-NF suggested the faster electron transfer rate and catalytic activity of hydrogen evolution reaction. An improved hydrogen production rate of 222 ± 20.3 mL H2 L−1 d−1 at 0.7 V applied voltage in fully assembled MECs was achieved for the outstanding hydrogen evolution performance of CoP-NF cathode, which was 3-fold superior to bare NF and even better than the Pt/C. The energy efficiency based on input electricity in the MECs equipped with the CoP-NF (90 ± 6.5%) was increased to twice as much as that Pt/C based cathodes. Long-term operation tests of MECs confirmed the superior stability of CoP-NF as an effective cathode in MECs for hydrogen production, suggesting its potential possibility in practical application.