High temperature electrolysis in alkaline cells, solid proton conducting cells, and solid oxide cells.

Sphere templating methods for periodic porous solids

An overview of cathode material and catalysts suitable for generating hydrogen in microbial electrolysis cell

Prospects for alkaline zero gap water electrolysers for hydrogen production

Microbial electrolysis cell (MEC) is a potentially attractive green technology to tackle the global warming and energy crisis, which employs electrochemically active bacteria to convert organic matter into hydrogen or a wide range of chemicals, such as methane, acetate, hydrogen peroxide, ethanol, and formic acid, without causing environmental pollution. Until now, probably the cleanest and the most efficient method of producing hydrogen has been MEC. However, this technology is still in its infancy period and poses various challenges towards up-scaling and widespread applications, such as such as lower hydrogen production rate (HPR), high internal resistance, complicated architecture, and expensive materials. New advances are needed in biofilm engineering, materials for electrodes and reactor configuration for successful real-world application of this technology. Thus, the present review deals with development of practical MEC technology and includes the following sections: firstly a general introduction to MECs; their operating principles, thermodynamics of MEC, and energy or voltage losses in the MEC system were provided. Followed by a section on the critical factors affecting MEC performance; microorganisms, anode, cathode, membrane or separator, fuel sources, the state-of-art MECs designs, other key operational factors, and its potential application in microbial production of value added products are discussed in detail. Afterwards, current challenges involved in developing practical MEC systems are highlighted, and outlooks for future development are also suggested. The review aims to assist researcher and engineers to gain fundamental understandings of MEC, and it also provides several future research directions and a road map on how to overcome the barriers, so the MEC technology can be further advanced and applied in larger scale.

Recent advances and emerging challenges in microbial electrolysis cells (MECs) for microbial production of hydrogen and value-added chemicals

The utilization of the inner surfaces of hydrogen-evolving, porous, sintered-nickel electrodes and Raney nickel-coated electrodes was investigated and compared by steady-state voltammetry, impedance spectroscopy, coulometric determination of catalyst surface, and scanning electron microscopy. Porous, sintered-nickel electrodes are shown to be utilized only to approximately 10%. On the time average, roughly 90% of the inner surface of these electrodes is gas-blanketed. Nanoporous, smooth Raney nickel coatings are divided by micron-scale cracks. The essential part of the catalytically active electrode surface of Raney nickel coatings is represented by the walls of nanopores whose diameter is around 2 nm. Tafel slopes of less than {minus}120 mV/dec, namely, {minus}50 to {minus}70 mV/dec, are measured at 50 {micro}m thick smooth Raney nickel coatings. These low Tafel slopes are explained by an increasing degree of nanopore utilization with increasing current density rising from less than 0.6 to {approximately}10% if the overpotential rises from {minus}30 to {minus}120 mV. The effect can be modeled for nanopores and is at variance with known micropore behavior under concentration polarization known for increased Tafel slopes. From pore modeling it follows also that in another type of Raney nickel coatings, the so-called composite coating composed of micrometer particles of Raney nickel, differentmore » from smooth Raney nickel coatings, the utilization of that part of particles which is contacted by the electrolyte is almost 100%. Since, as in sintered electrodes, only 10% of the particle surface are expected not to be gas-blanketed, the total utilization of composite coated nanoporous catalysts amounts to {approximately} 10%, independent of overpotential and current density.« less

H. Wendt

Papers

Morphology and utilization of smooth hydrogen-evolving Raney nickel cathode coatings and porous sintered-nickel cathodes

Morphology and Utilization of Smooth Hydrogen-Evolving Raney Nickel Cathode Coatings and Porous Sintered-Nickel Cathodes.