NSTF Advances for PEM Electrolysis - the Effect of Alloying on Activity of NSTF Electrolyzer Catalysts and Performance of NSTF Based PEM Electrolyzers

Recent resurgence of interest in harnessing energy from renewable sources, and a push to achieve environmental cleanliness in the energy industry has rekindled interest in hydrogen as a clean and environmentally benign energy carrier. This is done with the ultimate goal of supplanting the current hydrocarbon based economy by hydrogen economy as means to achieve environmentally friendly energy industry and energy independence. The rising star of hydrogen enabled mobility i.e. recent accomplishments in (automotive) fuel cells adds further impetus to advance renewable and at the same time economical means to generate hydrogen – i.e., which is the ultimate key to success for hydrogen as fuel in societal everyday transportation solutions.

As such, this rekindled interest in the age-old water electrolysis process spawned new approaches to generate hydrogen with increased efficiency and lower cost. Polymer electrolyte membrane (PEM) water electrolysis, while one of those relatively new approaches, has been used for quite a few years now without undergoing any substantial improvements over those years. Solutions based on Nafion 117 and high loadings of Platinum-Group Metals (PGM) worked well enough and were sufficiently durable. Now, however, with the new focus on hydrogen as the energy carrier (as opposed to a chemical reactant, mobile phase, or coolant – its major applications at present), there is much more interest in low cost/high efficiency H₂ production. This explains the renewed interest and recent increase in R&D activity in this fertile and promising area. As a matter of fact it is quite possible the success (or lack of) in achieving lower cost of hydrogen production may make or break the success of fuel cell as grid-level energy storage solution and personal transportation technology of choice.

There are two main ways to lower the cost of hydrogen production via PEM water electrolysis: to lower the capital expenses (CAPEX) and/or to lower the operating expenses (OPEX). We at 3M have recently addressed reducing the first (high CAPEX ) by widening the range of current densities where electrolyzers can operate from a maximum of about 2.0 A/cm², as used today in commercial electrolyzers, to as much as 20 A/cm². While the research on high power density operation of PEM water electrolysis still continues, and many questions remain as yet unanswered, the NSTF catalyst, with its highly conductive, compact, and hydrophilic catalyst layer seems uniquely fitting to the task. Indeed, its hydrophilicity that is a major weakness in fuel cells is a tremendous strength in water electrolysis and one of the features enabling the extremely high mass transport free current densities we reported previously¹. Currently, we intend to tackle the second means for reduction of cost of hydrogen production by increasing the intrinsic activity of the catalyst as means to increase the kinetics of oxygen evolution and hence the efficiency of water electrolysis (thus reducing the OPEX). We will show the effect of alloying on the performance of typical PGM based NSTF anode catalysts. One such example will be exploration of the Pt/Ir compositional parameter space (in the NSTF alloy catalyst format) and the compositional effects on fundamental catalyst activity, as determined by RDE measurements. Subsequently, we will correlate this to the in-situ performance measurements in a PEM electrolysis cell. Finally, we will discuss the possibilities in other promising alloying compositions and structures.

 

1. Krzysztof A. Lewinski, Sean M. Luopa, “High Power Water Electrolysis as a New Paradigm for Operation of PEM Electrolyzer.”, Spring ECS Meeting, Chicago, IL, May 2015.