David W. Gotthold

Molecular Dynamics Simulations Reveal that Water Diffusion between Graphene Oxide Layers is Slow.

Membranes made of stacked layers of graphene oxide (GO) hold the tantalizing promise of revolutionizing desalination and water filtration if selective transport of molecules can be controlled. We present the findings of an integrated study that combines experiment and molecular dynamics simulation of water intercalated between GO layers. We simulated a range of hydration levels from 1 wt.% to 23.3 wt.% water. The interlayer spacing increased upon hydration from 0.8 nm to 1.1 nm. We also synthesized GO membranes that showed an increase in layer spacing from about 0.7 nm to 0.8 nm and an increase in mass of about 15% on hydration. Water diffusion through GO layers is an order of magnitude slower than that in bulk water, because of strong hydrogen bonded interactions. Most of the water molecules are bound to OH groups even at the highest hydration level. We observed large water clusters that could span graphitic regions, oxidized regions and holes that have been experimentally observed in GO. Slow interlayer diffusion can be consistent with experimentally observed water transport in GO if holes lead to a shorter path length than previously assumed and sorption serves as a key rate-limiting step.

Cost Study for Manufacturing of Solid Oxide Fuel Cell Power Systems

Executive Summary Solid oxide fuel cell (SOFC) power systems can be designed to produce electricity from fossil fuels at extremely high net efficiencies, approaching 70%. However, in order to penetrate commercial markets to an extent that significantly impacts world fuel consumption, their cost will need to be competitive with alternative generating systems, such as gas turbines. This report discusses a cost model developed at PNNL to estimate the manufacturing cost of SOFC power systems sized for ground-based distributed generation. The power system design was developed at PNNL in a study on the feasibility of using SOFC power systems on more electric aircraft to replace the main engine-mounted electrical generators [Whyatt and Chick, 2012]. We chose to study that design because the projected efficiency was high (70%) and the generating capacity was suitable for ground-based distributed generation (270 kW). The electricity costs for a mass manufactured solid oxide fuel cell could be competitive with centralized power production plants with costs estimated to be in the

Anomalous water expulsion from carbon-based rods at high humidity

0.07-0.08/kWh range based on a cost model using a standard approach to manufacturing solid oxide fuel cells. A process flow sheet was developed to understand the steps required to manufacture the units, as well as to estimate the materials, equipment, and labor required to make them. Equipment was sized to meet a production volume of 10,000 units per year. Appropriate material and equipment prices were collected. A sputtering approach was also examined using the model to project the decreases in costs associated with the process. The process not only reduces material costs but increases the power density of the fuel cell by 50%. The increased power density reduces the number of repeat units required to make up the 270 kW fuel cell stack. Stack costs decreased by 33%. However, due the BOP and the remainder of costs associated in power system manufacturing and installation, the cost of electricity was only reduced by

Graphene oxide membranes with high permeability and selectivity for dehumidification of air

0.002/kWh. In addition, to the 10,000 units per year production scale model was adjusted to reflect the costs of production at 50, 250, 1000 and 4000 units of production per year. Material prices were adjusted to reflect purchase levels. Machinery and labor were adjusted to reflect the production scale.

Spectroscopic Study of Graphene Oxide Membranes Exposed to Ultraviolet Light

Three water adsorption-desorption mechanisms are common in inorganic materials: chemisorption, which can lead to the modification of the first coordination sphere; simple adsorption, which is reversible; and condensation, which is irreversible. Regardless of the sorption mechanism, all known materials exhibit an isotherm in which the quantity of water adsorbed increases with an increase in relative humidity. Here, we show that carbon-based rods can adsorb water at low humidity and spontaneously expel about half of the adsorbed water when the relative humidity exceeds a 50-80% threshold. The water expulsion is reversible, and is attributed to the interfacial forces between the confined rod surfaces. At wide rod spacings, a monolayer of water can form on the surface of the carbon-based rods, which subsequently leads to condensation in the confined space between adjacent rods. As the relative humidity increases, adjacent rods (confining surfaces) in the bundles are drawn closer together via capillary forces. At high relative humidity, and once the size of the confining surfaces has decreased to a critical length, a surface-induced evaporation phenomenon known as solvent cavitation occurs and water that had condensed inside the confined area is released as a vapour.