Research Advances towards Low Cost, High Efficiency PEM Electrolysis

Abstract

Water electrolysis has benefits over other hydrogen generation technologies due to the lack of carbon footprint when integrated with a renewable source of energy. Specifically, proton exchange membrane (PEM) electrolysis is a promising technology for hydrogen generation applications because of the lack of corrosive electrolytes, small footprint, and ability to generate at high pressure, requiring only deionized water and an energy source. PEM electrolysis also produces very pure hydrogen, with none of the typical catalyst poisons that may be found in hydrogen produced from reforming. However, significant advances are required in order to in order to provide a cost-competitive hydrogen source for energy markets. This paper will discuss the current limitations and recent work by Proton Energy Systems towards reaching the DOE Hydrogen Program objective for distributed production of hydrogen from distributed water electrolysis of $3.70/gge by 2012. Status of TechnologyProton exchange membrane (PEM) electrolysis has been known for over 50 years, starting from GE technology. Proton Energy Systems is currently the world leader in manufacturing of PEM hydrogen generation products using electrolysis, with over 1300 units in the field. Pure hydrogen is used in a variety of industrial applications, including acting as a cooling fluid for power plant turbine generators, a reducing atmosphere for heat treating and semiconductor processing, and as a carrier gas for spectroscopic applications such as gas chromatography. Proton's on site hydrogen generators are costcompetitive with delivered hydrogen for these applications. However, interest in hydrogen for energy applications has increased the need to decrease capital cost and increase efficiency of electrolysis and other generation methods. PEM vs. AlkalineThere are two main types of low temperature electrolysis currently commercially available. Alkaline electrolysis uses liquid electrolyte, with high concentrations of potassium hydroxide to provide ionic conductivity and to participate in the electrochemical reactions. PEM electrolysis replaces the liquid electrolyte with a solid polymer electrolyte, which selectively conducts positive ions such as protons. The protons participate in the water-splitting reaction instead of hydroxide, creating a locally acidic environment in the cell.There are advantages and disadvantages of each system. One advantage of KOH electrolyzers is the stability of nickel and stainless steel in this environment, enabling elimination of expensive materials of construction. However, in the KOH system, the

Critical Review—Identifying Critical Gaps for Polymer Electrolyte Water Electrolysis Development

“…12,29,30 The latter can be alleviated using reinforced membranes. 12 The higher gas crossover of thinner membranes can be addressed by incorporating a H 2 -O 2 recombination catalyst, e.g. Pt or Pd, into the membrane.…”

“…However, on the prototype level direct electrochemical compression in PEWEs up to 700 bar (differential) pressure has been demonstrated. 12,58,59 Theoretically, the compression loss in a PEWE can be predicted by the Nernst equation (see Equations 4 and 5), where for the calculation of the equilibrium potential assumptions for the activity of gases and water need to be made. For the solubility of hydrogen and oxygen in water up to 100 bar ideal gas behavior for both H 2 and O 2 can be assumed, [60][61][62] because at thermodynamic equilibrium conditions only the dissolved gas in the water is in contact with the electrodes.…”

“…While the increasing thermodynamic cell voltage can largely be seen in the differential pressure operation, demonstrated up to 700 bar, 12,58,59,63 as well as in electrochemical hydrogen compressors, 56,57 in experimental data of pressurized PEWE with balanced gas pressures, at relevant current densities, the cell voltage increase with operating pressure is often not observed. [64][65][66] In this case, processes with a negative overpotential vs. pressure relation are compensating the higher thermodynamic cell voltage.…”

“…11 Therefore, this review predominantly focuses on the polymer electrolyte water electrolyzer (PEWE) using a proton exchange membrane (PEM) c , yet prospects of alkaline membrane electrolysis are given where deemed appropriate. Due to the use of a membrane electrolyte, the PEWE can be operated at differential pressures of 100 bar or more, 12 which is of interest if hydrogen is the main product. Furthermore, oxygen production at low or ambient pressure reduces the constraints on the oxygen subsystem of the balance of plant components.…”

Electrochemical Hydrogen Compression: Efficient Pressurization Concept Derived from an Energetic Evaluation

“…For the 1/10 Nafion 112 membrane the faradaic efficiency at 100 MPa increases to above 96% from less than 70% for the standard material ( Figure 5B). Improvements in the membrane permeability seem to be possible by reinforcing the membrane 27 or by replacing the perfluoroalkylsulfonic acid based membranes with different chemistry, e.g. hydrocarbons.…”