Overview of Fuel Cell Technologies and the Major Scientific Challenges
Materials Sciences Division, Lawrence Berkeley National Laboratory Berkeley CA 94720
Fuel cells have been under intensive development for terrestrial use ever since the successful debut of the technology in the Apollo program. The first commercial fuel cell was offered by United Technologies from the early 1980’s, operating on natural gas, with an operating temperature range of 160 – 190 C, in modular sizes varying from 40 kW to 250 kW, and overall thermal efficiency of ca. 40 %. Larger units (2 MW) based on molten carbonate electrolyte operated at higher temperatures, ca. 650 C, had higher thermal efficiencies (ca. 55 %) but much higher capital cost. Both technologies have high capital cost (> $ 2500 per kW) that limits the applications to the premium power market, e.g. off-the-grid power for data centers. Lower temperature fuel cells operating on pure hydrogen have emerged in the last decade as an exploratory zero-emission power source for vehicles. Cost is still a major challenge, as well as the reliance on relatively large (20 times that in a conventional ICE vehicle) amount of platinum as the catalyst in the fuel cell. A scientific challenge in all these fuel cell technologies is the catalysis of the oxygen electrode, and the central role of the superoxide anion as an intermediate. Understanding the interaction of transition metal cations with this intermediate is essential to developing a robust non-Pt catalyst for low temperature fuel cells. Both quantum chemical and experimental studies of the superoxide anion intermediate will be reviewed.
Solid-State Batteries and Soft X-ray Spectroscopy
Nitash P. Balsara
University of California at Berkeley
All commercial batteries contain a liquid electrolyte. Our work is concerned with the development of solid electrolytes for rechargeable lithium batteries. The lack of a liquid makes these systems ideally suited for soft X-ray scattering experiments.
In Situ Measurements of Oxidation States and Potentials in MIEC Electrodes for Solid Oxide Electrochemical Cells
University of Maryland, College Park, MD,
Ambient pressure X-ray photoelectron spectroscopy (XPS) measurements at ALS beamlines 9.3.2 and 11.0.2 on thin-film undoped and gadoliunium-doped ceria electrodes have explored how surface oxidation states are impacted by overpotentials during both H2 oxidation and H2O electrolysis. For undoped ceria electrodes deposited on YSZ electrolyte supports, single-chamber tests with Pt counter electrodes in H2/H2O mixtures showed highly reduced surfaces (65 to 85% Ce3+) at zero-bias between 630 and 750 ºC. The degree of surface reduction in undoped ceria increased with positive cell bias driving H2O electrolysis and decreased with negative bias for H2 electrochemical oxidation on the ceria. Distribution of surface oxidation states and surface potentials (measured by KE energy shifts of photoelectron spectra) revealed ~150 µm-wide regions of electrochemically activity due to mixed ionic-electronic conductivity (MIEC) of ceria. More recent tests on gadolinium-doped ceria (GDC) thin-film electrodes in single-chamber tests at beamline 9.3.2 at similar conditions have shown that the present of the Gd3+ reduces the sensitivity of surface oxidation states with electrical bias and reduces electrochemical activity for H2O electrolysis. The simulateneous electrochemical and XPS measurements at ALS have provided critical insight into the behavior of these MIEC electrodes and established a basis for improving models of these materials in solid oxide electrochemical cells.
Large scale electronic structure calculations for electrochemistry problems
Computer Research Division, Lawrence Berkeley National Laboratory
I will present a brief review for the current status of large scale electronic structure calculations which might be relevant to electrochemistry problems and soft X-ray spectroscopy. The first is direct ab initio molecular dynamics simulation based on density functional theory. I will discuss about its size and time limitations as well as its accuracy. The second is classical force field (or reaction force field) simulations. I will discuss about its challenges. The third method is linear scaling electronic structure calculations. I will discuss its potential use in battery simulations. Finally, I will discuss some possible algorithms for large system soft X-ray calculations.
In operando Investigation of a Pt Anode Using Electrochemical Ambient Pressure XPS (EC-APXPS) in a Novel Two-Environment Chamber
Anthony H. McDaniel
Sandia National Laboratories, Livermore, CA
Electrochemical technologies will be increasingly used to supply energy to the world without contributing to climate change. These technologies can store and convert energy with unsurpassed efficiencies through, for example, the charging and discharging of batteries or the inter-conversion of electrical and chemical energy via fuel cell and electrolyzer. Perhaps the most important phenomena to understand in electrochemical energy storage/conversion is how electric charge is transferred across interfaces and subsequently stored in material phases and/or double layers. Specific questions include: 1) what chemical species transfer charge, 2) where is charge transferred in the heterogeneous system and 3) which reactions limit rates? Addressing these critical questions is challenging because of the physical complexity of these systems, which consist of a variety of electrified materials undergoing chemical reactions, as well as the difficulties associated with making meaningful in operando observations. For example, traditional diagnostics of electrochemistry, such as impedance spectroscopy, do not directly reveal the chemical information needed to resolve detailed kinetic pathways of surface electrochemistry.
In collaboration with the ALS, we have developed an approach that simultaneously characterizes chemical information and accurately measures electrical potentials in systems with condensed-phase electrolytes. EC-APXPS measurements reveal 1) the chemical identity of adsorbates, 2) the chemical state of the active materials and 3) how electric potential is distributed through the functioning materials. This important information is obtained simultaneously with traditional electrical characterization in gas environments of several torr, which is sufficient pressure to generate meaningful electrical current from the gas/surface reactions. We will describe a novel vacuum chamber design that uses a hermetically sealed membrane of electrolyte to fully isolate the gas environment of the anode from that of the cathode. The discussion will focus on the use of this apparatus to determine how adsorbates on the Pt electrocatalyst (anode) change with cell voltage during the generation of load current.
Acknowledgments: F. El Gabaly, J. Whaley, and Kevin McCarty from Sandia; M. Grass, Z. Liu, and H. Bluhm from Lawrence Berkeley National Laboratory.
In Situ Soft X-ray Spectroscopy of a Water-Oxidizing Electrocatalyst
Benedikt Lassalle,1 Jan Kern,1 Jeng-Lung Chen,2 Per Anders Glans,2 Wei-Cheng Wang,2 Vittal Yachandra,1 Jinghua Guo,2 Junko Yano1
1. Physical Biosciences Division, and 2. ALS LBNL, Berkeley, CA 94720
Water oxidation catalysts are currently a point of interest because of their potential involvement in clean fuels generation, such as in fuel cells or electrolysers. Catalysts used thus far for this reaction are precious metals, the price of which is prohibitory for wide-spread use. Therefore, there has been a recent increase in research efforts to replace the noble metals by more cheap earth-abundant metals. A recent report by the group of Nocera at MIT showed the water-splitting properties of an amorphous cobalt and nickel thin layers deposited onto Indium-Tin oxide (ITO) electrodes. In an effort to understand the structure of those layers under real time catalytic conditions, we used an in situ electrochemical setup developed at beamline 7.0.1 at the ALS. This cell features a Si3N4 window separating the UHV chamber from the ambient pressure electrochemical cell. Thin layers of titanium (4nm) and gold (10nm) deposited on this window form the working electrode, thus allowing a direct probe of the electrode chemistry. We deposited on this electrode a Ni catalyst layer and recorded its Ni L-edge and O K-edge spectra at potentials corresponding to the resting, pre-catalytic and catalytic states. Significant shifts are observed depending on the potential applied, both for the Ni L and O K edges. These results corroborate previous results obtained with hard X-rays at beamline 10.3.2 at the ALS, and allow us to attribute without ambiguity the oxidation state of the different intermediate of the catalyst. Work is in progress to identify the intermediate states of the water-oxidation catalytic cycle and the mechansim of the water-oxidation chemistry.
In Situ Soft X-ray Spectroscopy for Electrochemical Studies
Material Science Division, Lawrence Berkeley National Laboratory
The investigation of electrochemical reactions at the electrode and electrolyte interfaces is of importance not only for fundamental electrochemistry, but also for the development of electrochemical applications, such as Li ion batteries, supercapacitors, fuel cells and solar cells. In this talk, I will demonstrate a novel liquid flow cell for in situ photon-in photon-out soft x-ray spectroscopic studies under controlled electrochemical conditions. This setup allows real time monitoring of the element specific electronic structure changes of a system at all stages of the electrochemical cycle. This development will help elucidate the fundamental electrochemical processes for various electrochemical reactions.