Physicochemical Properties and Low Relative Humidity Fuel Cell Performance of Pt/ECSTM Catalysts

Abstract

The maturity of the current polymer electrolyte membrane fuel cells (PEMFCs) has been product of the considerable scientific and industrial effort devoted to developing highly efficient and reliable versions of this technology, resulting in its increased application in the transportation and energy generation sectors. Fuel cells are one of the most advantageous solutions for clean energy applications due to their near-zero-emission, high efficiency, low maintenance cost, and high energy density. PEMFCs produce electricity through the electrochemical reaction of hydrogen and oxygen (or air) taking place in the Membrane Electrode Assembly (MEA) by converting chemical energy of the hydrogen oxidation and oxygen reduction into electrical energy with water as a byproduct. However, producing oxygen reduction reaction (ORR) catalysts with high performance at scale is still a challenge that needs to be tackled to enable an increment in energy generation of this technology. Additionally, tunability of the materials at the core of this technology is essential to meet the demands of the specific application and operating conditions. Here we investigate commercially available ORR catalysts based on platinum nanoparticles (Pt-NPs) supported on nitrogen-functionalized carbon (Engineered Carbon SupportsTM, ECSTM) produced by Pajarito Powder, LLC at scale. The ORR performance of three MEAs made with different Pt/ECS catalysts, by IRD Fuel Cells, LLC was studied under low relative humidity conditions, exhibiting competitive performance, and reaching current densities between 1.8 and 1.3 A/cm2 at 0.6 V, at extremely low loading of Pt – 0.1 mgPt cm-2. The physicochemical properties of these Pt/ECS catalysts alongside their Pt-free ECSTM analogue carbon support materials were comprehensively studied. For this purpose, several characterization techniques were used, such: X-ray diffraction, Raman spectroscopy, and transmission electron microscopy (TEM) to investigate structural and morphological properties, X-ray photoelectron spectroscopy to determine the surface composition and chemical properties, thermogravimetric analysis to evaluate thermal oxidation properties, and nitrogen sorption to determine the surface area and porosity, of the materials. This thorough characterization enabled us to determine that the best performing catalyst in the conditions used in this work have the highest surface area and the highest concentration of surface dopants (nitrogen and oxygen). Although, catalyst supported on lower surface area carbon, but with higher graphitic content, also exhibited competitive performance that can be exploited in applications where more corrosion-resistant carbon is needed. Finally, based on the highly competitive MEA performance for the three Pt/ECS catalysts supported on these carbons, our work demonstrates that these carbon supports (developed by Pajarito Powder, LLC) with engineered morphology and composition fabricated through VariPoreTM synthetic technology can result in tunable properties suitable for a targeted application. We can conclude that these commercially available materials can be adapted through modification of the versatile synthesis platform to tune the physiochemical properties of carbons for other applications and conditions.