18b MEMBRANES FOR ELECTROCHEMICAL ENERGY STORAGE APPLICATIONS – Polymeric membranes for solar fuels generators -Novel dense-PBI membranes for photoelectrochemical hydrogen production

Recent studies seem to suggest that distributed and semi-central hydrogen production systems have potential in the near to mid-term for small/medium scale market penetration. Photoelectrochemical (PEC) water splitting has been considered the ultimate method to produce hydrogen as well as other fuels, directly from solar radiation. The process is simple and has potential for high conversion efficiency and low operating temperatures using cost-effective thin-film and/or particle semiconductor materials. Late R&D activities resulted in remarkable PEC system improvements in terms of efficiency, durability, and lifetime. One of the key components of the PEC system is the membrane separator, which still requires additional development to improve high ionic transport, reduced gas permeability, and elevated stability in corrosive and acidic environments. Greenway Energy (GWE), in conjunction with the University of South Carolina (U of SC), proposes the development of a novel polymeric membrane class, referred to as acid-doped dense polybenzimidazole (D- PBI) membrane, to be employed in a monolithically integrated PEC system for hydrogen production. The proposed membranes will allow the PEC system to operate at higher temperatures (on the order of 200 °C), resulting in remarkable increase of the overall hydrogen production efficiency, reduction of kinetic overpotential and increase of reactive mixture diffusion in the vapor phase. The work carried out in Phase 1 will focus on: (1) synthesis and production of novel polybenzimidazole membranes based on acid-doped formulations (D-PBI), (2) comprehensive characterization of the proposed membranes, both in terms of mechanical/structural properties and in terms of electrochemical properties, including initial durability performance testing, (3) screening of the main promising formulations, achieving selected targets, including proton conductivity, hydrogen and oxygen permeability, current density and performance degradation and (4) initial testing of the down selected membrane formulations, integrated in a simplified PEC device, under transient conditions and simulated on-sun conditions. Phase 2 work will be based on Phase 1 results and will aim to perform: (1) comprehensive testing of the membranes, including long term (> 1500 hours) durability testing, (2) identification of the interaction with current and novel photocatalysts, screened through a high-throughput approach, and (3) on-sun testing of a one-cell PEC device. The work will be carried out with the NREL (for membrane and PEC testing) and ANL (for photocatalyst development in Phase 2). The achievement of the proposed targets in the project will allow a comprehensive and definitive demonstration of novel separation membranes, based on the PBI configuration. The proposed membranes, initially developed and adopted for PEC devices, will also be employed in many different applications, ranging from traditional water electrolyzers to solar driven PEC for fuel (e.g., hydrocarbons) production. The activities will be carried out leveraging the outcomes and inputs from the DOE-EERE HydroGEN 2.0 Consortium, finding solutions for producing hydrogen, with direct coupling with solar inputs.