The Effect of Alloying with Non-PGM Transition Metals on the Activity of Ir-Nstf Electrolyzer Catalysts

Abstract

The interest in harnessing energy from renewable sources and a push to achieve environmental cleanliness in the energy industry keeps gaining momentum. The need to be able to convert and store all that renewable energy has rekindled interest in hydrogen as a clean and environmentally benign energy carrier. In fact, hydrogen seems to be the only energy storage medium capable of handling the vast grid-scale energy storage in a reasonable manner. Likewise, recent accomplishments in auto-motive fuel cells adds further impetus to advance simultaneously renewable and economical hydrogen generation technology, which will be the ultimate key to success for hydrogen as fuel in societal everyday transportation solutions. All this is done with the ultimate goal of supplanting the current hydrocarbon based economy by hydrogen economy as means to achieve globally environmentally friendly energy industry and regional/local energy independence. This recent increase in significance placed on the age-old water electrolysis process gave rise to new approaches to generate hydrogen with increased efficiency and lower cost. Polymer Electrolyte Membrane (PEM) water electrolysis emerged as one of the best matched choices today for the highly variable and unpredictable nature of the renewable energy. 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 showed a way to address reducing the first (high CAPEX ) by successfully demonstrating the ability to widen the range of current densities where electrolyzers can operate from a previous maximum of about 2.0 A/cm2 as used today in commercial electrolyzers, to as much as 20 A/cm2 in our novel constructions. While the research on high power density operation of PEM water electrolysis still continues and many questions remain as yet unanswered, the 3M’s proprietary Nano Structured Thin Film (NSTF) catalyst with its highly conductive, compact, and hydrophilic catalyst layer seems uniquely fitting to the task. Indeed, its hydrophilicity, which is perhaps a major challenge in fuel cells, is a tremendous strength and asset in PEM water electrolysis and one of the features enabling the extremely high virtually mass transport free current densities we reported previously1. In this work, we intend to present results from our attempts to tackle the second means to reduce the cost of hydrogen production (the OPEX), by increasing the intrinsic activity of the catalyst as means to increase the kinetics of oxygen evolution and hence the efficiency of water electrolysis. In the preceding work we have explored the Pt/Ir compositional parameter space (in the NSTF alloy catalyst format) and the compositional effects on fundamental catalyst activity, as determined by Rotating Disk Electrode (RDE) measurements and the evaluation of single electrolyzer cells2,3. That work has shown, rather unexpectedly we must add, quite detrimental effects of alloying basic Ir-NSTF catalyst with Pt in RDE tests. The results were confirmed, and perhaps even more drastic, when catalyst compositions were tested for performance in the actual electrolyzer hardware. Now, we intent to show the effect of alloying Ir with sample of non-PGM transition metals (again, using 3M’s proprietary Ir-NSTF catalyst format) and the effects of such alloys on the basic catalytic activity. 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, (invited) “High Power Water Electrolysis as a New Paradigm for Operation of PEM Electrolyzer” (abstract 1948), Spring ECS Meeting, Chicago, IL, May 2015. 2. Krzysztof A. Lewinski, Dennis van der Vliet, and Sean M. Luopa, “NSTF Advances for PEM Electrolysis - the Effect of Alloying on Activity of NSTF Electrolyzer Catalysts and Performance of NSTF Based PEM Electrolyzers” ( 1457), Fall ECS Meeting, Phoenix, AZ, Oct 2015. 3. Krzysztof A. Lewinski, Dennis van der Vliet, and Sean M. Luopa, “NSTF Advances for PEM Electrolysis - the Effect of Alloying on Activity of NSTF Electrolyzer Catalysts and Performance of NSTF Based PEM Electrolyzers”, (10.1149/06917.0893ecst), ECS Transactions, 69 (17) , p. 893-917 (2015).