(Olin Palladium Award of the Electrochemical Society) Polymer Electrolyte Fuel Cells: Recognition of a Field of Electrochemistry for Technical Contributions Made by Outstanding Technical Teams

Abstract

The Olin Palladium medal is being awarded at this ECS meeting for projects I have been involved with over the last 35 years, mostly in the field of polymer electrolyte fuel cells (PEFCs). The great advancement of this technology over that period of time, has been the product of outstanding R,D&E work by several teams of scientists and engineers. I believe ECS is recognizing today the impressive advancements in this field of electrochemistry and, particularly, the scientists and engineers who enabled these advancements culminating in reduction to practice of 100 kW level PEFC power sources for electric vehicles (FCEVs). I feel I am receiving this award for the community of key contributors to this field of electrochemistry and I am honored to represent them here. Serving over the years as Technical Team Leader in a series of PEFC R,D&E projects, I learnt to fully recognize the interdisciplinary nature of this technology and the resulting impact on technology development. The foundations for the science and technology of polymer electrolyte fuel cells are provided by a significant number of fields , including: * Catalysis at the solid/electrolyte interface as practiced with nano-dispersed catalyst particles, * ionic and electronic conductivity of mixed conductors, * technology of ionomeric membranes and the science of the water/ionomer system, * physics and chemistry of high surface area carbons, *kinetics of multistep electrochemical processes, * modeling of complex systems involving combined physical & chemical processes, *structural materials and advanced methods of metal forming, *metal corrosion and chemical decay of ionomers and polymers and, * Analysis and design of energy conversion systems. Good control of a wider spectrum of these technical disciplines by members of a fuel cell technical team, carries great value in facilitating communication between technical staff members of different backgrounds and, in intensifying fruitful exchange. A wider “personal horizon” should indeed be assigned special weight in consideration of candidates for staff positions in such teams. My talk in this session will offer a brief survey of PEFC technology highlights over the past 35 years. Starting with the important contributions of the LANL team in the 1980s and 1990s, the development and demonstration of thin film catalyst layers with loading of <0.5mgPtcm-2 had special significance. The catalyst layer has been typically prepared by ultrasound-mixing of an ionomer dispersion and a carbon-supported Pt catalyst , forming a catalyst ink to be applied to the membrane surface. Catalyst layers so prepared indeed enabled achievement of several watts per cm2 using just ~0.5mgPtcm-2. Moving next fast forward to 2015 , a bolder target of ultra-low Pt loading for transport applications (~0.1mgPtcm-2 ) resulted in performance limitations at high current densities, apparently caused by (i) limited rate of oxygen transport through a thin film of ionomer around the catalyst particle and, (ii) catalyst surface deactivation caused by such ionomer coat. A remediation described recently, targets placing the metal catalyst nanoparticle “side-by-side” with a nano-grain or, nano-patch of the ionomer, achieving such nano-separation by using HSACs as catalyst support (GM 2016, Kofu Univ., 2016 and TUM ,2017). With this last development taking place 25 years after the first introduction of low Pt loading technology, some comments will be offered on the dynamics of PEFC science and technology development. Looking for a cost-effective alternative to the PEFC , CellEra (Israel) started in 2010 development of fuel cell technology based on hydroxide ion conducting membranes (HEMFCs) which should allow use of Pt-free electrodes. HEMFCs present some significant technical challenges, including water management and carbonation by CO2 in the air feed stream. Efforts at Cellera (now POCellTech) resulted in HEMFC performance on hydrogen and air (CO2-free) equivalent to that of a PEMFC using similar ultra-low PGM loading of <0.1 mg Pt/cm2. Consequently, advantages of the lower HEMFC stack materials cost can be now realized. A new approach (UDel,2018 ) to the removal of CO2 from the air supply stream by electrochemical pumping, will be described. An activity to be described last , started in 2015 and is devoted to direct ammonia fuel cells (DAFCs) with an alkaline membrane electrolyte , operating around 100°C. A team involving BNL, POCellTech and UDel, demonstrated very recently power density of 600 mW/cm2 generated by such an ammonia/oxygen cell operating near 100°C. Being a carbon-free fuel which is liquefiable at ambient temperature under relatively low pressures, liquid ammonia has been considered recently as a possible medium for storage and distribution of the hydrogen to be made from renewable resources (EPRI Report , 2019).