Free air breathing planar PEM fuel cell design for portable electronics

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (leaf 33).PEM fuel cell technology is an energy source that can provide several times more energy per unit volume then current lithium ion batteries. However, PEM fuel cells remain to be optimized in volume and mass to create a minimum size for integration into portable electronics. A planar fuel cell design utilizes the bare minimum in volume and mass over current stacked fuel cell designs. This was done by taking an innovative approach of assembling the fuel cell with just the bare minimum components, a proton exchange membrane, cathode electrode, anode electrode, and gas diffusion layer on both sides of the membrane to assume the role of GDL and current collector. This planar fuel cell design was able to produce a power density over 25mW/cm2. This is an order of magnitude lower then reported air breathing fuel cell values, however the route cause has been isolated to the ohmic losses of the planar fuel cell. Increasing the applied contact forces and creating low resistance electronically conductive grid lines, have shown to contribute to the reduction in ohmic resistance and will be the focus of future research. From this research, a planar fuel cell design has been shown to successful work and there are ways to improve its performance.by Ethan J. Crumlin.S.B

Architectures for individual and stacked micro single chamber solid oxide fuel cells

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 97-102).Solid oxide fuel cells (SOFCs) are electrochemical conversion devices that convert various fuel sources directly into electrical energy at temperatures ranging from 600°C to 1000°C. These high temperatures could potentially allow the direct use of various hydrocarbon fuel sources and hydrogen, without the need for expensive noble metal catalysis. Conventional SOFCs are designed in a two-chamber system, separating the fuel and oxidant flow to the anode and cathode, respectively. However, fuel cell manufacturing cost and robustness have proven to be the main challenges to rapid commercialization. A promising alternate method to achieve these requirements and to open up new architecture designs for the SOFC is the development of single-chamber solid oxide fuel cells (SC-SOFCs). SC-SOFCs avoid many of the manufacturing challenges associated with conventional SOFCs, and have shown optimal performance between 500°C and 800°C. This reduces the need for high temperature sealing and a complicated manifold structure; however it also reduces the partial pressure of the gases at the electrodes, which reduces the theoretical obtainable voltage.(cont.) Microfabrication techniques such as photolithography, sputtering, and photo-resist liftoff were used to create various micro SC-SOFC that are 25-400microns long and 15-40microns wide, utilizing platinum and gold for the electrodes and YSZ as the electrolyte. After successfully fabricating these micro SC-SOFCs, the fuel cells were tested in a microprobestation with a custom gas chamber enclosure, which was exposed to CH4:02:N2 at 20:20:100 ccm or 40:20:100 ccm. A switch in the OCV from a negative voltage to a positive voltage was observed around 600°C, possible indicating change in electrochemical reactions with temperature. An OCV of [approx.] 0.4V and peak power density of 27[mu]W/cm2 at 900°C in a 1:1 methane:oxygen ratio was achieved. A stack of 10 micro SC-SOFCs as fabricated showing a cumulative OCV of 3.3 V, of an average 0.33 V per cell at 600°C in a 2:1 methane:oxygen ratio. Ongoing research will involve characterizing micro SC-SOFCs to understand the fundamental reaction mechanisms, electrode materials, and architectures to obtain dense, high performing stacks of micro SC-SOFCs.by Ethan Jon Crumlin.S.M

Fundamental studies of heterostructured oxide thin film electrocatalysts for oxygen reduction at high temperatures

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references.Searching for active and cost-effective catalysts for oxygen electrocatalysis is essential for the development of efficient clean electrochemical energy technologies. Perovskite oxides are active for surface oxygen exchange at evaluated temperatures and they are used commonly in solid oxide fuel cells (SOFC) or electrolyzers. However, the oxide surface chemistry at high temperatures and near ambient oxygen pressure is poorly understood, which limits the design of highly active catalysts. This work investigates heterostructured interfaces between (Lai. xSrx)CoO 3-3 (where x = 0.2 and 0.4, LSC80-2011 3 and LSC60-40 113 respectively) and (Lao. 5 Sro.5 )2CoO 4 ,3 (LSC2 14) enhanced ORR catalytic activity 1) via electrochemical impedance spectroscopy, atomic force microscopy, scanning electron microscopy, scanning transmission electron microscopy, and high resolution X-ray diffraction (HRXRD) and 2) using in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) and in situ HRXRD. Here we show that the ORR of epitaxial LSC80-20 1 3 and LSC60-40113 is dramatically enhanced (~3-4 orders of magnitude above bulk LSC113) by surface decorations of LSC214 (LSC 1 31214) with coverage in the range from ~0.1 to ~15 nm. Such high surface oxygen kinetics (~ 110-5 cm-s1 at 550 C) are among the most active SOFC cathode materials reported to date. Although the mechanism for ORR enhancement is not yet fully understood, our results to date show that the observed ORR enhancement can be attributed to highly active interfacial LSCn 13/LSC214 regions, which were shown to be atomically sharp. Using in situ HRXRD and APXPS we show that epitaxial LSC80-20n3 thin films have lower coverage of surface secondary phases and higher Strontium enrichment in the perovskite structure, which is attributed to its markedly enhanced activity relative to LSC80-20113 powder. APXPS temperature cycling of epitaxial LSC80-20113 APXPS reveled upon heating to 520 *C the initial Sr enrichment which is irreversible, however subsequent temperature cycling demonstrates a small amount of reversible Sr enrichment. With applied potentials LSC80- 2013/214 shows significant Sr enrichment greater then LSC80-20 113, and the ability to stabilize high concentrations of both lattice and surface Sr which we hypothesize is a very important factor governing LSC80-2011 3214 enhanced ORR activity.by Ethan Jon Crumlin.Ph.D

Insights into Electrochemical Reactions from Ambient Pressure Photoelectron Spectroscopy

The understanding of fundamental processes in the bulk and at the interfaces of electrochemical devices is a prerequisite for the development of new technologies with higher efficiency and improved performance. One energy storage scheme of great interest is splitting water to form hydrogen and oxygen gas and converting back to electrical energy by their subsequent recombination with only water as a byproduct. However, kinetic limitations to the rate of oxygen-based electrochemical reactions hamper the efficiency in technologies such as solar fuels, fuel cells, and electrolyzers. For these reactions, the use of metal oxides as electrocatalysts is prevalent due to their stability, low cost, and ability to store oxygen within the lattice. However, due to the inherently convoluted nature of electrochemical and chemical processes in electrochemical systems, it is difficult to isolate and study individual electrochemical processes in a complex system. Therefore, in situ characterization tools are required for observing related physical and chemical processes directly at the places where and while they occur and can help elucidate the mechanisms of charge separation and charge transfer at electrochemical interfaces.National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program)Skoltech-MIT Center for Electrochemical Energy StorageUnited States. Department of EnergyNational Energy Technology Laboratory (U.S.)Solid State Energy Conversion Alliance. Core Technology Program (DEFE0009435

An Operando Investigation of (Ni-Fe-Co-Ce)O_x System as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is a critical component of industrial processes such as electrowinning of metals and the chlor-alkali process. It also plays a central role in the developing renewable energy field of solar-fuels generation by providing both the protons and electrons needed to generate fuels such as H_2 or reduced hydrocarbons from CO_2. To improve these processes, it is necessary to expand the fundamental understanding of catalytically active species at low overpotential, which will further the development of novel electrocatalysts with high activity and durability. In this context, performing experimental investigations of the electrocatalysts under realistic working regimes, i.e. under operando conditions, is of crucial importance. Here, we study a highly active quinary transition metal oxide-based OER electrocatalyst by means of operando ambient pressure X-ray photoelectron spectroscopy and X-ray absorption spectroscopy performed at the solid/liquid interface. We observe that the catalyst undergoes a clear chemical-structural evolution as a function of the applied potential with Ni, Fe and Co oxy-hydroxides comprising the active catalytic species. While CeO_2 is redox inactive under catalytic conditions, its influence on the redox processes of the transition metals boosts the catalytic activity at low overpotentials, introducing an important design principle for the optimization of electrocatalysts and tailoring of novel materials

Subsurface oxide plays a critical role in CO_2 activation by Cu(111) surfaces to form chemisorbed CO_2 , the first step in reduction of CO_2

A national priority is to convert CO_2 into high-value chemical products such as liquid fuels. Because current electrocatalysts are not adequate, we aim to discover new catalysts by obtaining a detailed understanding of the initial steps of CO_2 electroreduction on copper surfaces, the best current catalysts. Using ambient pressure X-ray photoelectron spectroscopy interpreted with quantum mechanical prediction of the structures and free energies, we show that the presence of a thin suboxide structure below the copper surface is essential to bind the CO_2 in the physisorbed configuration at 298 K, and we show that this suboxide is essential for converting to the chemisorbed CO_2 in the presence of water as the first step toward CO_2 reduction products such as formate and CO. This optimum suboxide leads to both neutral and charged Cu surface sites, providing fresh insights into how to design improved carbon dioxide reduction catalysts

Initial steps in forming the electrode electrolyte interface: H_2O adsorption and complex formation on the Ag(111) surface from combining Quantum Mechanics calculations and X-ray Photoelectron Spectroscopy

The interaction of water with metal surfaces is at the heart of electrocatalysis. But there remain enormous uncertainties about the atomistic interactions at the electrode–electrolyte interface (EEI). As the first step toward an understanding of the EEI, we report here the details of the initial steps of H_2O adsorption and complex formation on a Ag(111) surface, based on coupling quantum mechanics (QM) and ambient-pressure X-ray photoelectron spectroscopy (APXPS) experiments. We find a close and direct comparison between simulation and experiment, validated under various isotherm and isobar conditions. We identify five observable oxygen-containing species whose concentrations depend sensitively on temperature and pressure: chemisorbed O* and OH*, H_2O* stabilized by hydrogen bond interactions with OH* or O*, and multilayer H_2O*. We identify the species experimentally by their O 1s core-level shift that we calculate with QM along with the structures and free energies as a function of temperature and pressure. This leads to a chemical reaction network (CRN) that we use to predict the time evolution of their concentrations over a wide range of temperature (298–798 K) and pressure conditions (10^(–6)–1 Torr), which agree well with the populations determined from APXPS. This multistep simulation CRN protocol should be useful for other heterogeneous catalytic systems