We report an interesting new class of bifunctional electrocatalysts, Pd/C-CeO2, with excellent activity and stability for the hydrogen oxidation reaction (HOR) under alkaline conditions. The unique structure of palladium deposited onto a mixed support of Vulcan XC-72 carbon and CeO2 consists of Pd metal preferable deposited on the ceria regions of the catalyst. The CeO2-Pd interaction leads to enhanced HOR kinetics and increased stability. Here we compare catalysts with three different Pd loadings and show that the 10 wt% Pd sample has optimized activity. Hydrogen pumping and fuel cell experiments based on this catalyst show higher activities as compared to a Pd/C sample without ceria. Metal dissolution tests and identical location transmission microscopy experiments show that the catalyst stability under harsh potential cycling experiments in alkaline medium is significantly improved as compared to Pd/C, making this material one of the best options for use as highly active and highly stable electrocatalysts for the HOR in anion exchange membrane fuel cells

Phosphoric acid fuel cells are successfully used as energy conversion technologies in stationary power applications. However, decreased proton conductivity and lower oxygen permeability of phosphoric-acid-imbibed membranes require prohibitive loadings of the traditional noble-metal-based electrocatalyst, such as platinum supported on carbon. Additionally, specific adsorption of phosphate anions on the catalyst results in a surface poisoning that further reduces electrocatalytic activity. Here we report a nonplatinum group metal (non-PGM) electrocatalyst as an alternative cathode electrocatalyst for oxygen reduction in phosphoric acid fuel cells. The non-PGM was prepared in a one-pot synthesis using a metal organic framework and iron salt precursor. Phosphate anion poisoning was monitored electrochemically and spectroscopically in reference to the current state-of-the-art Pt-based catalyst at room temperature. Unlike Pt-based catalysts that are prone to phosphate poisoning, the non-PGM electrocatalyst exhibits immunity to surface poisoning by phosphate anions at room temperature. Imaging with microscopy reveals that the iron particles are isolated from the electrolyte by graphitic layers, which ultimately protect the iron from phosphate anion adsorption. The non-PGM electrocatalyst represents the highest performance to date in a high-temperature phosphoric acid membrane system, which is likely attributed to its immunity to phosphate adsorption at the harsher fuel cell environments.

Electrospun nanofiber cathode mats were prepared with a metal‐organic framework (MOF)‐derived Fe−N−C catalyst and a blended binder of Nafion and polyvinylidene fluoride (PVDF). The electrodes were incorporated into H2/air fuel cell membrane‐electrode assemblies (MEAs) and compared with conventional sprayed‐cathode MEAs, in terms of power output and durability. The addition of hydrophobic PVDF into the electrode binder of nanofiber and sprayed cathodes produced a stable power output for 300 hours, whereas the sprayed‐electrode MEA with neat Nafion binder exhibited a 63 % power loss. The steady‐state maximum power density output of a PGM‐free nanofiber‐cathode MEA with a 1 : 1 Nafion : PVDF cathode binder at 80 °C and 1 atm backpressure was 154 mW/cm2. MEAs with a nanofiber cathode generated significantly more power than a sprayed cathode and the nanofiber cathodes continued to produce power throughout a carbon‐corrosion voltage cycling accelerated‐stress test. After 50 carbon corrosion‐voltage cycles, the maximum power density rose from 154 to 186 mW/cm2 and then decreased to 106 mW/cm2 at 500 cycles.

Mass transport properties of a pair of non-Platinum Group Metal (non-PGM) catalysts in proton exchange membrane fuel cells (PEMFCs) were evaluated through methods developed by Reshetenko et al., demonstrating that the use of different carrier gases can allow for the determination of the mass transport coefficient for oxygen in the gas phase and the electrolyte phase. The gas-phase and non-gas-phase resistances can be elucidated from the slope and intercept, respectively, of the total mass transport coefficient plotted as a function of molecular weight. It was determined through these experiments that the primary sources of mass transfer limitations of the non-PGMs when compared to the PGMs were the catalyst layer (non-gas-phase), rather than the flow fields (gas-phase, primarily Knudsen Diffusion effects), and the gas diffusion layer. This work was combined with a pseudo-2D, isothermal, steady state numerical model to estimate the gas-phase mass transfer coefficient and the fraction of hydrophobic, gas-phase pores in the catalyst layer. Sensitivity studies were also carried out, allowing for more information regarding the influence of several inherent factors on the mass transport limitations, and allow for additional validation of the model beyond simply the quality of the fit.

The high mass and volume-specific energy of dimethyl ether (DME) relative to hydrogen make it an attractive alternative electrochemical fuel source for portable applications such as powering drones and eVTOLs. A key stumbling block to the development of direct DME fuel cells (DDMEFCs) is the poisoning of the electrocatalyst surface by oxidation intermediates such as CO ads . In this study, an all-queous colloidal synthesis method for producing highly dispersed Pt 2 Bi alloy nanoplatelets (NPT) to mitigate such poisoning is presented. NPT synthesis entails the use of stannous chloride as an autocatalytic reducing and stabilizing agent for both Pt and Bi salts in aqueous solution. Sn and Bi stripping from the surface of these NPT is found to maximize activity for DME electrooxidation (DMEOR) relative to commercial Pt-C. A stable chronoamperometric current of 3.3 A g Pt −1 (15.8 μA cm Pt −2 ) is observed at the peak CO ads -stripping potential of 0.7 V vs RHE at 50 °C over a time interval where Pt-C activity becomes negligible. The response of anodic peak positions to potential sweep rates is used to reveal the impact of alloying (electronic structure) on the electro-oxidation rates of various intermediate species on Pt 2 Bi NPT. Resistance to poisoning coincides both with a reduction in the C ads specific activity onset potential by 25 mV relative to Pt-C and faster DME electro-oxidation kinetics. DDMEFC testing of the unsupported Pt 2 Bi NPT utilizing a phosphoric acid-doped polybenzimidazole (PBI) membrane operating at 240 °C yields a peak power of 56 W g PGM,anode −1. This represents a 30% increase relative to a commercial PtRu catalyst.

Electrochemical hydrogen pumps (EHP) provide a unique highly efficient means of separating and compressing hydrogen with continuous steady-state operation. Here, we demonstrate the performance of a commercially available polybenzimidazole (PBI) membrane-based platform as a benchmark for ultra-high efficiency performance. A primary gas mixture of CO2 and H2 with a ratio of 4:1, respectively, was selected to demonstrate the performance of EHPs with near theoretical Faradaic efficiency with negligible CO poisoning due to reverse water gas shift reaction. It was found that humidification of the feed gas at room temperature improved polarization performance while also improving energy efficiency, thus reducing the need for a tightly controlled relative humidity of feed gas. A new perspective on EHP energy efficiency calculation methodology is also provided by including the cell heating requirement in the calculation. In this manner, an overall improvement to the energy efficiency of nearly 20% was realized by dropping the cell temperature to 120°C while paying no significant penalty to electrochemical performance. Nearly 99.99% pure H2 and 99.93% pure CO2 were produced with a hydrogen yield of 99.34%.

No abstract

AcknowledgementsIn reality, there are far more people that deserve recognition here than can possibly be acknowledged. But first and foremost I must acknowledge my parents, Glenn Pavlicek and Anita Penta, for their unconditional support over the years. Without their input and encouragement, I never would have even started this process. And so many times over these years, they have been the rock on which I leaned during difficult stretches. My father was always there to provide advice on handling the pressures and needs of a PhD, and my mother was invaluable in helping me deal with the emotional stress of the workplace. And as this time came closer to its conclusion, both were key resources while my post-graduation plans came together.Prof. Sanjeev Mukerjee afforded me the incredible opportunity of working with him and the NUCRET research group. This lab has become a second (and sometimes primary) home over the past five years. I cannot thank him enough for the rigorous and demanding nature with which he has run the NUCRET group. It certainly has not been an easy process, and at times I questioned the path I had chosen. However, now that this journey has come to an end, it certainly is not possible that I would have reached this point without taking this rigor installed by him, and adopting it in my studies. Dr. Serge Pann cannot go without mention in the NUCRET lab, as he has played a vital role in the operations of the NUCRET lab over the last few years, both from an overarching and day-to-day aspect. Bob Allen has been a valuable asset over the past few years as a resource for unlimited knowledge on the history of catalyst synthesis and fuel There are too many friends and family to name everyone that has been there over these past six years. My brother Garrett has always been a great reprieve from stressful times when home at the holidays. Andrew Sheridan, Licole Paroly, Emily Callen, Thomas Tran, and Paulina Tuy have been the best group of friends and fellow beer enthusiasts anyone could ask for.Steven Bennett, Justin Hurley, Brian Martin, George Leonard, Joe Seymour, Charles Liu, Anthony Zhang, Mohit Raghunathan, and Jarrod Coleman are amongst those from CMU who've help provide some much needed short vacations over the years. 5Last but certainly not least, a huge thank you to my girlfriend Rachael Hasse, who has seen the best and worst of me over the final year of my work here at Northeastern. She has known exactly when to be the encouraging force to keep going, and when to tear me away from work when it was needed. I don't think I would have gotten through this last year and the stress of writing and defending my thesis while preparing for my post graduate student life without her contributions. 6 Abstract of DissertationToday's high and growing energy demands are unsustainable given the cost and depleting nature of fossil fuel sources, and has long been accepted as a major factor in climate change.Due to these factors, alternative clean and renewable energy sources have long been an interest in both academ...