Energy Systems, Thermodynamic, and Financial Analysis of Low Temperature, Proton-Conducting Electrochemical Hydrogen Compressors (EHCs) for Distributed Energy Storage

Abstract

This research analyses the potential for compressing hydrogen (H2) with low temperature, proton-conducting electrochemical hydrogen compressors (EHCs). Energy systems analysis, thermodynamic, and financial models are developed to analyse EHC systems in terms of their future engineering and economic performance. Currently, most EHCs are at an early technology readiness level (TRL); i.e. individual cells and stacks have been tested in controlled, laboratory environments. This work analyses state-of-the-art, best performing EHC cells, stacks, and systems, tested to-date in the laboratory, and projects their performance into the future for large-scale, commercial EHC systems for distributed energy storage. EHCs use electricity to split hydrogen molecules (H2) into hydrogen ions (H+) and electrons (e-). The overall, endothermic reaction is Electricity + H2 (low pressure) → H2 (high pressure). A power source delivers direct current (DC) electricity to the EHC electrodes such that, at the anode, H2 at low pressure split into H+ and e-. The e- flow through an external circuit, and the H+ flow through an electrolyte selectively conductive to H+. At the cathode, the H+ and e- recombine to form H2 at high pressure. EHCs can generate high purity, high pressure H2. The theoretical efficiency of EHCs is higher than that of mechanical piston and/or diaphragm compressors because they compress in a manner that is isothermal, rather than isentropic. This analysis focuses on low-temperature EHCs using proton-conducting membrane electrolytes. This research deploys custom-built energy systems analysis, thermodynamic, and financial models, as well as a U.S. Department of Energy (DOE) techno-economic modelling tool for H2 compression, called the HDSAM Model. The HDSAM Model captures a set of standard DOE assumptions and methods. When these standards are adhered to, using the HDSAM Model can facilitate more even-handed techno-economic comparisons of a variety of H2 compression, storage, and dispensing technologies. This analysis deploys energy systems analysis, thermodynamic, and financial models, including the HDSAM model, to evaluate H2 compression based on EHCs powered by electricity from the grid. Models were developed to describe small-scale, 2,400 kilograms (kg) H2/day, EHC compression systems envisioned for both the near and far-term futures. Model results indicate that, for an average electricity cost of about $0.06/kilowatt-hour (kWh), the levelized cost of compressing H2 with a state-of-the-art EHC systems could be as low as ~$0.50/kg H2 in the near-term. The levelized cost of compressing the H2 is most strongly influenced by the electricity price. Electricity costs constitute roughly 65% of the levelized cost. The levelized cost of compressing H2 is also impacted by the EHC system’s capital cost and the EHC’s electrical efficiency. Capital costs constitute roughly 35% of the levelized cost. Fixed operations and maintenance costs and other variable costs are negligible.