Study of impact of mesh structure on electrolysis cells performance

Microbial electrolysis cells or MECs provide a high yield method for hydrogen production from different organic substrates, like wastewater and other biomass. Bacteria on the anode oxidize the organic matter and transform energy present in biodegradable substrate in current. With a small electrical input, hydrogen can be produced on the cathode under anoxic conditions, often with the help of a catalyst.

While diverse advancements in MEC performance have been made, creating an economical, scalable design is a critical challenge for the MEC to become a proven technology for hydrogen production. The cathode count be responsible for the maximum amount of total capital costs for the cells.

Nickel based alloys have shown a reliable electrocatalytic activity for the hydrogen production reaction in water electrolysis. Affordableand reliable mesh electrode made from stainless steel 304 with high nickel concentration is commercially available as an alternative to Nickel alloy. It shows good catalytic activation in an alkaline solution. In the neutral pH conditions, the maximum hydrogen production rate received was 1.7 m3 of H2/ m3 d and overall energy efficiency of 78% using the high surface area stainless steel 304 brushes at an applied voltage of 0.6V. It is better than that received with platinum-catalyzed flat carbon cloth cathode, showing that costly precious metals are not required. Although a widely complex structure of an MEC with brushes may limit this mechanism.

A linear sweep voltammetry is used to evaluate the current densities of various mesh and bubble properties were observed at different applied voltages.

Stainless steel mesh as in woven and expanded metal forms is used for its suitability as cathodes in Microbial electronic cells. Woven mesh and expanded mesh are expected to have effects on current densities due to bubble developed causing the difference between mesh functions. Both mesh forms have the same chemistry as of stainless steel 304 and are hence expected to have the same hydrogen production activation energies.

MECs are single-cell, cubic type reactors, they operate in fed-batch mode. To prevent gas accumulation between the mesh cathode and end plate on the top of the cylinder, a part of the top of mesh is cut and bent into the solution to ensure no loss in surface area.

Woven mesh shows higher increase in current as compare to expanded mesh. It is found that expanded produces current significantly lower than woven mesh at higher current density vales. Larger current per applied voltage of produced by mesh could introduce larger active surface areas than those estimated or different effects of structures on hydrogen bubble release. Depending on the outstanding performance of woven mesh, expanded mesh is not evaluated further.

Mesh configuration has significant impact on current. At low current density value, small hydrogen bubbles at low surface coverage occurs on the different mesh. With increase in applied current, the bubbles expand until their size is comparable to the mesh pore size. At the highest current density, the bubbles coalesce and quickly brake down from the surface, decreasing the overall bubble coverage.