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Alkaline and acid-alkaline bipolar membrane electrolytes were prepared from cast and electrospun polymer membranes. The alkaline anion-exchange membrane (AEM) consisted of a polyphenylene oxide (PPO) backbone containing side-chain alkyl amine groups of various lengths. Different AEM membranes were investigated to down-select to a stable chemistry for preparing the acid-alkaline bipolar membrane. Nafion 117 was utilized as the proton-exchange membrane (PEM) component, and the PEM was joined to the AEM to form a PEM-AEM acid-alkaline bipolar membrane electrolyte. Different methods for joining the PEM-AEM were evaluated to determine compatibility matching between layers. In some cases, an electrospun layer junction between the PEM-AEM was created to assist in development. In-plane and through-plane ionic conductivity measurements were performed to evaluate the isolated AEM, PEM and PEM-AEM membranes.

Proton-exchange membrane fuel cells (PEMFCs) generally contain platinum-group-metal (PGM) electrocatalysts supported on a variety of different carbons. However, the long term durability of PGM electrocatalysts is decreased due to carbon support corrosion and loss of the electrochemically active surface area (ESA) as a result of nanoparticle agglomeration and/or Ostwald ripening. Moreover, the prohibitive expense of PGM materials has forced consideration of non-PGM alternatives. One way to mitigate carbon corrosion and increase long-term operation is by using metal oxide supports. For example, Huang et al. compared PEMFC performance of Pt/TiO2 to Pt/C (TKK) after subjecting both catalysts to an accelerated stress testing (AST) protocol, and found that Pt/TiO2 catalyst essentially retained its ESA and prevented Pt nanoparticle agglomeration. Wu et al. studied the oxygen reduction reaction (ORR) in 0.5 M H2SO4 on Fe-containing carbonized polyaniline supported on TiO2 (PANI-FeTiO2), and found an onset and half-wave (E1/2) potential of 0.98 and 0.83 V vs. RHE, respectively. The authors found that the PANI-Fe-TiO2 catalyst showed better results than Pt/C, and suggested that adding TiO2 not only decreased carbon corrosion but facilitated the ORR. In this study, we focus on developing durable non-PGM electrocatalysts for PEMFCs. We carbonize electrospun polyacrylonitrile (PAN) carbon nanofibers (CNFs) and coat them with TiO2 using atomic layer deposition (ALD). Furthermore, we enhance the surface area and reactive edges of the CNFs by adding nitrogendoped graphene platelets to the surface with a plasmaenhanced chemical vapor deposition (PECVD) process. PAN CNFs are attractive due to their inherent ORR activity and conductivity. Park et al. carbonized electrospun CNFs and reported a ~2x increase in bulk conductivity compared to XC-72R. The addition of TiO2 may act to alleviate carbon corrosion. We plan to study the ORR on TiO2-coated CNF/graphene electrocatalysts with rotating ring disk electrode (RRDE) voltammetry. Additionally, we attempt to compare the ORR activity for TiO2 coatings deposited with different ALD precursors. Physical characterizations such as XRD, XPS, TEM and SEM are performed to understand the electrocatalyst morphology, TiO2 loading and imaging, respectively. Figure 1a and 1b show carbonized PAN CNFs before and after growing graphene platelets onto the nanofiber walls, respectively.