Microbial Electrolysis Cells For Hydrogen Production Research Articles

Nanoporous oxide coating on carbon paper electrodes to enable bio-hydrogen production in microbial electrolysis cells

To counteract expensive cathodes, a single chamber microbial electrolysis cell (MEC) equipped with nanoporous oxide coating on a carbon paper electrode as a cathode was explored. The performance of the MEC was evaluated based on the chemical oxygen demand (COD) removal efficiency, catalytic activity, and hydrogen production. The obtained results indicated that nanoporous oxide coated carbon electrode with TiO2 achieved maximum H2 yield (3.0 mol H2 mol−1 acetate), followed by ZrO2 and SiO2. In contrast, the uncoated carbon electrode achieved lower hydrogen yield (0.08 mol H2 mol−1 acetate). A maximum COD removal of 82% was achieved from the carbon electrode coated with TiO2 followed by 80.5% from SiO2 and 79% from ZrO2. Additionally, based on linear sweep voltammetry, nanoporous oxide coated electrodes started H2 evolution at a lower potential than the uncoated electrode, thereby exhibiting a higher catalytic rate. This investigation showed that carbon electrodes with nanoporous coating can be one of the economical (low cost) and potential electrodes to be used as a cathode in the MEC for hydrogen production instead of expensive metallic electrodes.

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.

Nanoparticulate Ni(OH)2 Films Synthesized from Macrocyclic Nickel(II) Cyclam for Hydrogen Production in Microbial Electrolysis Cells

Hydrogen production in microbial electrolysis cells (MECs) is a promising approach for energy harvesting from wastewater. The kinetic barriers toward proton reduction necessitate the use of catalysts to drive hydrogen formation at appreciable rates and low applied potentials. Towards this end, cost effective alternatives to platinum catalysts are of paramount interest. In this study, Ni(OH)2 films were synthesized by electrophoretic deposition from a Ni(II)cyclam precursor solution at varying concentrations (6 mM, 15 mM, and 23 mM). The films were characterized by scanning electron microscopy and X-ray photo-electron spectroscopy to confirm the deposition of Ni(OH)2. The Ni(OH)2-modified electrodes were then examined by both traditional electrochemical measurements and in an MEC for hydrogen production. Tafel analysis indicates an exchange current density of ∼0.36 mA cm−2 with a Tafel slope of ∼120 mV decade−1 consistent with a rate determining proton adsoprtion step. The hydrogen production rates increased with increasing Ni(II)cyclam concentration in the precursor solution, with the 23 mM-derived film exhibiting a rate comparable to that of a Pt-based catalyst in MEC tests.

Hydrogen production in single chamber microbial electrolysis cells with stainless steel fiber felt cathodes

Microbial electrolysis cell (MEC) is a promising technology for sustainable production of hydrogen from biodegradable carbon sources. Employing a low-cost and high efficient cathode to replace platinum catalyzed cathode (Pt/C) for hydrogen generation is a challenge for commercialization of MEC. Here we show that a 3D macroporous stainless steel fiber felt (SSFF) with high electrochemical active surface area has an excellent catalytic activity for hydrogen generation, which is comparable to Pt/C cathode and superior to stainless steel mesh (SSM) cathode in the single-chamber MEC. The SSFF cathode (mean filter rating 100 μm) produces hydrogen at a rate of 3.66 ± 0.43 m3 H2 m−3d−1 (current density of 17.29 ± 1.68 A m−2), with a hydrogen recovery of 76.37 ± 15.04% and overall energy efficiency of 79.61 ± 13.07% at an applied voltage of 0.9 V. The performance of SSFF cathode improves over time due to a decrease in overpotential which caused by corrosion. These results demonstrate that SSFF can be a promising alternative for Pt catalytic cathode in MEC for hydrogen production.