Vilayanur V. Viswanathan

Stabilization of Electrocatalytic Metal Nanoparticles at Metal−Metal Oxide−Graphene Triple Junction Points

Carbon-supported precious metal catalysts are widely used in heterogeneous catalysis and electrocatalysis, and enhancement of catalyst dispersion and stability by controlling the interfacial structure is highly desired. Here we report a new method to deposit metal oxides and metal nanoparticles on graphene and form stable metal-metal oxide-graphene triple junctions for electrocatalysis applications. We first synthesize indium tin oxide (ITO) nanocrystals directly on functionalized graphene sheets, forming an ITO-graphene hybrid. Platinum nanoparticles are then deposited, forming a unique triple-junction structure (Pt-ITO-graphene). Our experimental work and periodic density functional theory (DFT) calculations show that the supported Pt nanoparticles are more stable at the Pt-ITO-graphene triple junctions. Furthermore, DFT calculations suggest that the defects and functional groups on graphene also play an important role in stabilizing the catalysts. These new catalyst materials were tested for oxygen reduction for potential applications in polymer electrolyte membrane fuel cells, and they exhibited greatly enhanced stability and activity.

LiMnPO4 Nanoplate Grown via Solid-State Reaction in Molten Hydrocarbon for Li~Ion Battery Cathode

Electrochemically active LiMnPO(4) nanoplates have been synthesized via a novel, single-step, solid-state reaction in molten hydrocarbon. The olivine-structured LiMnPO(4) nanoplates with a thickness of approximately 50 nm appear porous and were formed as nanocrystals were assembled and grew into nanorods along the [010] direction in the (100) plane. After carbon coating, the prepared LiMnPO(4) cathode demonstrated a flat potential at 4.1 V versus Li with a specific capacity reaching as high as 168 mAh/g under a galvanostatic charging/discharging mode, along with an excellent cyclability.

Second Use of Transportation Batteries: Maximizing the Value of Batteries for Transportation and Grid Services

Plug-in hybrid electric vehicles (PHEVs) and electric vehicles (EVs) are expected to gain significant market share in the next few decades. The economic viability for such vehicles is contingent upon the availability of cost-effective batteries with high power and energy density. For initial commercial success, government subsidies will be instrumental in allowing PHEVs and EVs to gain a foothold. However, in the long term, for electric vehicles to be commercially viable, the economics have to be self-sustaining. Toward the end of the battery life in the vehicle, the energy capacity left in the battery is not sufficient to provide the designed range for the vehicle. Typically, the automotive manufacturers recommend battery replacement when the remaining energy capacity reaches 70%-80%. There is still sufficient power (kilowatts) and energy capacity (kilowatthour) left in the battery to support various grid ancillary services such as balancing, spinning reserve, and load following. As renewable energy penetration increases, the need for such balancing services is expected to increase. This work explores optimality for the replacement of transportation batteries to be subsequently used for grid services. This analysis maximizes the value of an electric vehicle battery to be used as a transportation battery (in its first life) and, then, as a resource for providing grid services (in its second life). The results are presented across a range of key parameters, such as depth of discharge (DOD), number of batteries used over the life of the vehicle, battery life in the vehicle, battery state of health (SOH) at the end of life in the vehicle, and ancillary services rate. The results provide valuable insights for the automotive industry into maximizing the utility and the value of the vehicle batteries in an effort to either reduce the selling price of EVs and PHEVs or maximize the profitability of the emerging electrification of transportation.

On the use of energy storage technologies for regulation services in electric power systems with significant penetration of wind energy

Energy produced by intermittent renewable resources is sharply increasing in the United States. At high penetration levels, volatility of wind power production could cause additional problems for the power system balancing functions such as regulation. This paper reports some partial results of a project work, recently conducted by the Pacific Northwest National Laboratory (PNNL) for Bonneville Power Administration (BPA). The project proposes to mitigate additional intermittency with the help of Wide Area Energy Management System (WAEMS) that would provide a two-way simultaneous regulation service for the BPA and California ISO systems by using a large energy storage facility. The paper evaluates several utility-scale energy storage technology options for their usage as regulation resources. The regulation service requires a participating resource to quickly vary its power output following the rapidly and frequently changing regulation signal. Several energy storage options have been analyzed based on thirteen selection criteria. The evaluation process resulted in the selection of flywheels, pumped hydro electric power (or conventional hydro electric power) plant and sodium sulfur or nickel cadmium batteries as candidate technologies for the WAEMS project. A cost benefit analysis should be conducted to narrow the choice to one technology.

Redox Flow Batteries: An Engineering Perspective

Redox flow batteries are well suited to provide modular and scalable energy storage systems for a wide range of energy storage applications. In this paper, we review the development of redox-flow-battery technology including recent advances in new redox active materials, cell designs, and systems, all from the perspective of engineers interested in applying this technology. We discuss cost, performance, and reliability metrics that are critical for deployment of large flow-battery systems. The technology, while relatively young, has the potential for significant improvement through reduced materials costs, improved energy efficiency, and significant reduction in the overall system costs.

Energy Storage for Power Systems Applications: A Regional Assessment for the Northwest Power Pool (NWPP)

Wind production, which has expanded rapidly in recent years, could be an important element in the future efficient management of the electric power system; however, wind energy generation is uncontrollable and intermittent in nature. Thus, while wind power represents a significant opportunity to the Bonneville Power Administration (BPA), integrating high levels of wind resources into the power system will bring great challenges to generation scheduling and in the provision of ancillary services. This report addresses several key questions in the broader discussion on the integration of renewable energy resources in the Pacific Northwest power grid. More specifically, it addresses the following questions: a) how much total reserve or balancing requirements are necessary to accommodate the simulated expansion of intermittent renewable energy resources during the 2019 time horizon, and b) what are the most cost effective technological solutions for meeting load balancing requirements in the Northwest Power Pool (NWPP).

National Assessment of Energy Storage for Grid Balancing and Arbitrage: Phase 1, WECC

To examine the role that energy storage could play in mitigating the impacts of the stochastic variability of wind generation on regional grid operation, the Pacific Northwest National Laboratory (PNNL) examined a hypothetical 2020 grid scenario in which additional wind generation capacity is built to meet renewable portfolio standard targets in the Western Interconnection. PNNL developed a stochastic model for estimating the balancing requirements using historical wind statistics and forecasting error, a detailed engineering model to analyze the dispatch of energy storage and fast-ramping generation devices for estimating size requirements of energy storage and generation systems for meeting new balancing requirements, and financial models for estimating the life-cycle cost of storage and generation systems in addressing the future balancing requirements for sub-regions in the Western Interconnection. Evaluated technologies include combustion turbines, sodium sulfur (Na-S) batteries, lithium ion batteries, pumped-hydro energy storage, compressed air energy storage, flywheels, redox flow batteries, and demand response. Distinct power and energy capacity requirements were estimated for each technology option, and battery size was optimized to minimize costs. Modeling results indicate that in a future power grid with high-penetration of renewables, the most cost competitive technologies for meeting balancing requirements include Na-S batteries and flywheels.

Polarization Losses under Accelerated Stress Test Using Multiwalled Carbon Nanotube Supported Pt Catalyst in PEM Fuel Cells

The electrochemical behavior for Pt catalysts supported on multiwalled carbon nanotubes and Vulcan XC-72 in proton exchange membrane (PEM) fuel cells under accelerated stress test at 1.2 V was examined by cyclic voltammetry, electrochemical impedance spectroscopy, and polarization technique. Pt catalyst supported on multiwalled carbon nanotubes exhibited a highly stable electrochemical surface area, oxygen reduction kinetics, and fuel cell performance under highly oxidizing conditions, indicating multiwalled carbon nanotubes have a high corrosion resistance and a strong interaction with Pt nanoparticles. Further analyses were conducted using Tafel slope, ohmic resistances, and limiting current density were conducted for the multiwalled carbon nanotube supported Pt catalyst from the actual polarization curve to differentiate kinetic, ohmic, and mass-transfer polarization losses. It was found that kinetic contribution to the total overpotential was the largest throughout the stress test. However, during accelerated stress test, the fraction of kinetic overpotential decreased, the fraction of ohmic overpotential increased, and the fraction of mass-transfer overpotential remained relatively constant. The increased fraction of ohmic overpotential suggests increased proton transport limitation in the catalyst layer.

The Wide-Area Energy Storage and Management System – Battery Storage Evaluation

This report presents the modeling approach, methodologies, and results of the sodium sulfur (NaS) battery evaluation study, which was conducted by Battelle for the California Energy Commission (CEC).

Energy storage for variable renewable energy resource integration — A regional assessment for the Northwest Power Pool (NWPP)

This paper addresses the following key questions in the discussion on the integration of renewable energy resources in the Pacific Northwest power grid: a) what will be the future balancing requirement to accommodate a simulated expansion of wind energy resources from 3.3 GW in 2008 to 14.4 GW in 2019 in the Northwest Power Pool (NWPP), and b) what are the most cost effective technological solutions for meeting the balancing requirements in the Northwest Power Pool (NWPP). A life-cycle analysis was performed to assess the least-cost technology option for meeting the new balancing requirement. The technologies considered in this study include conventional turbines (CT), sodium sulfur (NaS) batteries, lithium ion (Li-ion) batteries, pumped hydro energy storage (PH), and demand response (DR). Hybrid concepts that combine 2 or more of the technologies above are also evaluated. This analysis was performed with collaboration by the Bonneville Power Administration and funded by the Energy Storage Systems Program of the U.S. Department of Energy.