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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Strategic Petroleum Reserve Cavern Leaching Monitoring CY21

Th e U.S. Strategic Petroleum Reserve (SPR) is a crude oil storage system administered by the U.S. Department of Energy. The reserve consists of 60 active storage caverns located in underground salt domes spread across four sites in Louisiana and Texas, near the Gulf of Mexico. Beginning in 2016, the SPR started executing C ongressionally mandated oil sales. The configuration of the reserve, with a total capacity of greater than 700 million barrels ( MMB ) , re quires that unsaturated water (referred to herein as ?raw? water) is injected into the storage caverns to displace oil for sales , exchanges, and drawdowns . As such, oil sales will produce cavern growth to the extent that raw water contacts the salt cavern walls and dissolves (leaches) the surrounding salt before reaching brine saturation. SPR injected a total of over 45 MMB of raw water into twenty - six caverns as part of oil sales in CY21 . Leaching effects were monitored in these caverns to understand how the sales operations may impact the long - term integrity of the caverns. While frequent sonars are the most direct means to monitor changes in cavern shape, they can be resource intensive for the number of caverns involved in sales and exchanges. An interm ediate option is to model the leaching effects and see if any concerning features develop. The leaching effects were modeled here using the Sandia Solution Mining Code , SANSMIC . The modeling results indicate that leaching - induced features do not raise co ncern for the majority of the caverns, 15 of 26. Eleven caverns, BH - 107, BH - 110, BH - 112, BH - 113, BM - 109, WH - 11, WH - 112, WH - 114, BC - 17, BC - 18, and BC - 19 have features that may grow with additional leaching and should be monitored as leaching continues in th ose caverns. Additionally, BH - 114, BM - 4, and BM - 106 were identified in previous leaching reports for recommendation of monitoring. Nine caverns had pre - and post - leach sonars that were compared with SANSMIC results. Overall, SANSMIC was able to capture the leaching well. A deviation in the SANSMIC and sonar cavern shapes was observed near the cavern floor in caverns with significant floor rise, a process not captured by SANSMIC. These results validate that SANSMIC continues to serve as a useful tool for mon itoring changes in cavern shape due to leaching effects related to sales and exchanges.

02 PETROLEUM↗
DOE OSTI2023

A Lattice Boltzmann Method for Predicting Porous Transport Layer Performance During Electrolysis

Electrolysis, the splitting of water into oxygen and hydrogen using electricity, is a sustainable way to produce green hydrogen for energy storage. In polymer electrolyte membrane (PEM) water electrolysis, water is brought into contact with charged catalyst layers and electrochemically separated into oxygen and hydrogen. The hydrogen product formed at the cathode is carried through the catalyst layer for eventual collection, while the oxygen by-product formed at the anode is removed from the surface via a multiphase interaction with circulating water and a solid porous transport layer (PTL). The design of this PTL aids in the detachment and advection of the oxygen by-product and thereby plays a role in the overall efficacy of the catalyst. In this presentation, we present our initial results modeling this multiphase system using a single-component, multiphase lattice Boltzmann method. We use the Shan-Chen model describing inter-particle forces to capture both the cohesion of the water (liquid) and oxygen (gas) phases and their interaction with the PTL (solid) (Shan and Chen, 1993). We use a Carnahan-Starling equation of state to model the effective density governing these inter-particle interactions which allows us to model this relatively high density ratio system (Carnahan and Starling, 1969). With these simulations, we show that the geometry and heterogeneity of the PTL geometry plays a large role in its ability to move oxygen away from the catalyst layer and the resulting bubble structures that are formed within the PTL. The current work demonstrates these effects using synthesized PTL geometries and 2D physics, which will be extended to experimentally-imaged PTL sections and 3D algorithms in the near future.

Boltzmann↗
DOE OSTI2026

Advancing hydrogen production: A comprehensive review of wastewater reforming techniques, feedstocks, and opportunities

Wastewater is produced across nearly all human activities and requires treatment to safeguard human health and the natural environment. Treatment of wastewater often requires a large amount of thermal energy, resulting in wasted heat after the treatment process. Because hydrocarbon reforming needs both water and heat, the integration of wastewater treatment with hydrocarbon reforming, a process that produces synthesis gas rich in hydrogen, offers an excellent opportunity to utilize this waste heat and the impurities in wastewater to produce valuable hydrogen gas, to minimize waste from industrial processes, and to integrate water treatment with the hydrogen economy. Yet, no comprehensive literature review has been conducted to examine the integration of reforming and wastewater. To address this lack, we summarize the variety of catalytic reforming techniques available in the open literature and review the current literature on wastewater reforming with these techniques. Subsequently, we conduct a review of common types of wastewater contaminants and their possible effects on reforming catalyst performance and life. Lastly, three underexamined wastewater sources are identified, namely, oilfield wastewater, geothermal water, and mining and mineral processing wastewater, and their potential for future study as a reforming feedstock is examined.

08 HYDROGEN↗
DOE OSTI2022

A reaction mechanism for plasma electrolysis of AgNO 3 forming silver nanoclusters and nanoparticles

In plasma-driven solution electrolysis (PDSE), gas-phase plasma-produced species interact with an electrolytic solution to produce, for example, nanoparticles. An atmospheric pressure plasma jet (APPJ) directed onto a liquid solution containing a metallic salt will promote reduction of metallic ions in solution, generating metallic clusters that nucleate to form nanoparticles. In this article, results from a computational investigation are discussed of a PDSE process in which a radio-frequency APPJ sustained in helium impinges on a silver nitrate solution, resulting in growth of silver nanoparticles. A reaction mechanism was developed and implemented in a global plasma chemistry model to predict nanoparticle growth. To develop the reaction mechanism, density functional theory was used to generate probable silver growth pathways up to Ag 9 . Neutral clusters larger than Ag 9 were classified as nanoparticles. Kinetic reaction rate coefficients for thermodynamically favorable growth pathways were estimated based on an existing, empirically determined base reaction mechanism for smaller Ag particle interactions. These rates were used in conjunction with diffusion-controlled reaction rate coefficients that were calculated for other Ag species. The role of anions in reduction of Agn ions in forming nanoparticles is also discussed. Oxygen containing impurities or admixtures to the helium, air entrainment into the APPJ, and dissociation of saturated water vapor above the solution can produce additional reactive oxygen species in solution, resulting in the production of anions and O 2 – in particular. For a given molarity, delivering a sufficient fluence of reducing species will produce similar nanoparticle densities and sizes for all applied power levels. In conclusion, comparisons are made to alternate models for nanoparticle formation, including charged nanoparticles and use of direct current plasmas.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Optimization of Water-Alternating-CO2 Injection Field Operations Using a Machine-Learning-Assisted Workflow

Summary This paper will present a robust workflow to address multiobjective optimization (MOO) of carbon dioxide (CO2)-enhanced oil recovery (EOR)-sequestration projects with a large number of operational control parameters. Farnsworth unit (FWU) field, a mature oil reservoir undergoing CO2 alternating water injection (CO2-WAG) EOR, will be used as a field case to validate the proposed optimization protocol. The expected outcome of this work would be a repository of Pareto-optimal solutions of multiple objective functions, including oil recovery, carbon storage volume, and project economics. FWU’s numerical model is used to demonstrate the proposed optimization workflow. Because using MOO requires computationally intensive procedures, machine-learning-based proxies are introduced to substitute for the high-fidelity model, thus reducing the total computation overhead. The vector machine regression combined with the Gaussian kernel (Gaussian-SVR) is used to construct proxies. An iterative self-adjusting process prepares the training knowledge base to develop robust proxies and minimizes computational time. The proxies’ hyperparameters will be optimally designed using Bayesian optimization to achieve better generalization performance. Trained proxies will be coupled with multiobjective particle swarm Optimization (MOPSO) protocol to construct the Pareto-front solution repository. The outcomes of this workflow will be a repository containing Pareto-optimal solutions of multiple objectives considered in the CO2-WAG project. The proposed optimization workflow will be compared with another established methodology using a multilayer neural network (MLNN) to validate its feasibility in handling MOO with a large number of parameters to control. Optimization parameters used include operational variables that might be used to control the CO2-WAG process, such as the duration of the water/gas injection period, producer bottomhole pressure (BHP) control, and water injection rate of each well included in the numerical model. It is proved that the workflow coupling Gaussian-SVR proxies and the iterative self-adjusting protocol is more computationally efficient. The MOO process is made more rapid by squeezing the size of the required training knowledge base while maintaining the high accuracy of the optimized results. The outcomes of the optimization study show promising results in successfully establishing the solution repository considering multiple objective functions. Results are also verified by validating the Pareto fronts with simulation results using obtained optimized control parameters. The outcome from this work could provide field operators an opportunity to design a CO2-WAG project using as many inputs as possible from the reservoir models. The proposed work introduces a novel concept that couples Gaussian-SVR proxies with a self-adjusting protocol to increase the computational efficiency of the proposed workflow and to guarantee the high accuracy of the obtained optimized results. More importantly, the workflow can optimize a large number of control parameters used in a complex CO2-WAG process, which greatly extends its utility in solving large-scale MOO problems in various projects with similar desired outcomes.

Energy & Fuels↗
DOE OSTI2021

Comparative Techno-Economic and Life Cycle Analysis of Water Oxidation and Hydrogen Oxidation at the Anode in a CO 2 Electrolysis to Ethylene System

We compare the economic viability of employing hydrogen oxidation versus water oxidation at the anode of a commercial-scale electrolysis plant that converts CO 2 to ethylene. We vary the electrolyzer capital cost, membrane lifetime, and renewable electricity price to represent a current and future market scenario. We find that anodic hydrogen oxidation with membraneless reactor design can reduce the electrolyzer capital cost by up to 48% and reduce electricity demand by at least 50% with the current underdeveloped electrolyzer market. These capital and operating cost savings could further lead to a lower ethylene production cost from anodic hydrogen oxidation than the anodic water oxidation system with hydrogen supplied at less than $\$6$ kg. In the future scenario with a fully developed electrolyzer market and cheap renewable electricity, we find that the anodic hydrogen oxidation system requires hydrogen cheaper than $0.7/kg to compete with the anodic water oxidation system. Moreover, hydrogen oxidation at the anode enables extremely low cradle-to-gate emission ethylene by utilizing negative emission hydrogen such as biomass gasification with carbon capture and sequestration, ~240% lower than ethylene produced from the wind/solar electricity-driven water oxidation system. Furthermore, this low carbon footprint ethylene can further boost the economic competitiveness for anodic hydrogen oxidation with a future carbon credit market.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Techno-economic analysis of offshore wind PEM water electrolysis for H 2 production

A model for producing hydrogen via offshore wind electrolysis was developed and the levelized costs of both energy and hydrogen were calculated. Here, this model calculated the cost of hydrogen produced by offshore wind and showed that the levelized cost of energy for hydrogen production and transportation to shore could be lower than for electricity transmission from offshore wind farms, using real wind data from a particular location. Therefore, direct coupling of the electrolysis system with offshore wind turbine is more advantageous than transmitting electricity to shore and then producing hydrogen via traditional electrolysis; the cost of hydrogen from offshore wind electrolysis is estimated to be $\$2.09$/kg, vs $\$3.86$/kg from traditional electrolysis using wind power.

08 HYDROGEN↗
DOE OSTI2022

A User Guide to PARET/ANL

PARET was originally created in 1969 at what is now Idaho National Laboratory (INL), to analyze reactivity insertion events in research and test reactor cores cooled by light or heavy water, with fuel composed of either plates or pins. The use of PARET is also appropriate for fuel assemblies with curved fuel plates when their radii of curvatures are large with respect to the fuel plate thickness. The PARET/ANL version of the code has been developed at Argonne National Laboratory (ANL) under the sponsorship of the U.S. Department of Energy/NNSA since the inception of the Reactor Conversion Program. Since Reduced Enrichment for Research and Test Reactors (RERTR) began in 1978, PARET/ANL has been benchmarked to experimental data including SPERT testing, and used to determine the expected transient behavior of a large number of reactors regardless of enrichment both inside and outside the Reactor Conversion Program. This document provides the pertinent information for the use of PARET/ANL Version 7.6. PARET/ANL models the various fueled regions of a reactor core as channels. Each of these channels consists of a single flat fuel plate/pin (including cladding and, optionally, a gap) with water coolant on each side. In slab geometry the coolant channels for a given fuel plate are of identical dimensions (mirror symmetry), but they can be of different thickness in each channel. There can be many channels, but each channel is independent and coupled only through reactivity feedback effects to the whole core. The time-dependent differential equations that represent the system are replaced by an equivalent set of finite-difference equations in space and time, which are integrated numerically. PARET/ANL uses fundamentally the same numerical scheme as RELAP5 for the time-integration of the point-kinetics equations. The one-dimensional thermal-hydraulic model includes temperature-dependent thermal properties of the solid materials, such as heat capacity and thermal conductivity, as well as the transient heat production and heat transfer from the fuel meat to the coolant. Temperature- and pressure-dependent thermal properties of the coolant such as enthalpy, density, thermal conductivity, and viscosity are also used in determining parameters such as friction factors and heat transfer coefficients. The code first determines the steady-state solution for the initial state. Then the solution of the transient is obtained by integration in time and space. Multiple heat transfer, DNB and flow instability correlations are available. The code was originally developed to model reactors cooled by an open loop, which was adequate for rapid transients in pool-type cores. An external loop model appropriate for Miniature Neutron Source Reactors (MNSR’s) was also added to PARET/ANL to model natural circulation within the vessel, heat transfer from the vessel to pool and heat loss by evaporation from the pool. PARET/ANL also contains models for decay heat after shutdown, control rod reactivity versus time or position, time-dependent pump flow, and loss-of-flow event with flow reversal as well as logic for trips on period, power, and flow. Feedback reactivity effects from coolant density changes and temperature changes are represented by tables. Feedback reactivity from fuel heat-up (Doppler Effect) is represented by a four-term polynomial in powers of fuel temperature. Photo-neutrons produced in beryllium or in heavy water may be included in the point-kinetics equations by using additional delayed neutron groups.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

48 Ca(p,pn) 47 Ca linac production for the preparation of a 47 Ca/ 47 Sc generator

Here, the production of 47 Sc via the nuclear reaction 48 Ca(p,pn) 47 Ca→(β-, T 1/2 = 4.54 d) 47 Sc and the assembly of a 47 Ca/ 47 Sc generator system has been investigated at Brookhaven National Laboratory. To produce 47 Ca, a pressed nat CaCl 2 target was irradiated with a proton beam at energy on target of 27.5 MeV at Brookhaven Linac Isotope Producer. Irradiated targets were dissolved in water and then acidified with concentrated HCl before separation using extraction chromatography through a diglycolamide (DGA) resin column. After ingrowth, 47 Sc was collected at >90 % with low contamination from both nonradioactive metals and coproduced radionuclides. A total of four 47 Ca/ 47 Sc separations were performed with 6–7 days between the irradiation and the separation to allow the equilibration of the ingrowing 47 Sc.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2024

Targeted synthesis, characterization, and electrochemical analysis of transition-metal-oxide catalysts for the oxygen evolution reaction

Hydrogen fuel can be produced through the electrochemical splitting of water, an energy-intensive process that requires the use of electrocatalysts to be more efficient. Whereas current precious-metal-based electrocatalysts might be costly on a larger scale, transition-metal-oxide catalysts are more earth abundant and have shown promising activity. Here, the development and improvement of highly active transition-metal-oxide electrocatalysts is thus an important area of study where different catalyst enhancement strategies are used to drive the field forward. Additionally, transition-metal-oxide catalysts come in various different structures with their own advantages; thus, this review is focused on investigating the continuing field of transition-metal-oxide electrocatalysts of different structures and innovative methods of improving activity. By the end, new and promising paths forward in this field will be highlighted, particularly in the development of rock-salt oxides for the water-splitting system.

08 HYDROGEN↗
DOE OSTI2021

Reactive oxygen species alter chemical composition and adsorptive fractionation of soil organic matter

Reactive oxygen species (ROS), formed during redox fluctuations in iron-rich soils, have been known to stimulate lignin degradation, although not much is known about how they alter soil organic matter (SOM) composition and interaction with mineral surfaces. We conducted a laboratory experiment to see how ROS altered SOM composition and adsorptive fractionation onto Fe-mineral surfaces. We reacted water extracts of SOM with ·OH, produced by the Fenton reaction, and then conducted a sorption experiment of the extracts with goethite to analyze the amount and quality of SOM adsorbed. The Fenton reaction preferentially consumed low-O, mostly aromatic molecules, and new high-O molecules were detected post-Fenton, nearly half of which were carbohydrate-like. Although the amount of C adsorbed did not change after oxidation, the post-Fenton adsorbed molecules were more oxidized. Pre-Fenton adsorption was dominated by aromatic molecules (90%), but post-Fenton, the adsorbed molecules were 75% aromatic and 25% carbohydrate-like. We show that the ·OH radical oxidized SOM and shifted patterns of adsorption to a more oxidized pool. Because adsorption to minerals is thought to stabilize SOM, our results suggest that ROS may alter the availability and stabilization patterns of SOM.

Patel, Kaizad F.↗
DOE OSTI2023

Cost analysis of hydrogen production by high-temperature solid oxide electrolysis

In this study, we estimate construction and operation costs of gigawatt-scale solid oxide electrolysis (SOE) facilities for producing high purity hydrogen gas from water. Manufacturing and assembly costs for two types of SOE cell stacks are estimated using a detailed design for manufacture and assembly (DFMA®) analysis. Modular balance of plant (BOP) process equipment is designed and sized with Aspen®, and cost estimated using equipment vendor quotes. Factory and on-site assembly and installation costs for SOEC stack and BOP equipment integration into modular SOE process units are calculated using a simplified DFMA® method. Total stack costs on a stack input power (SIP) basis reduce to <$100/kW e DC SIP for >500 MW e DC SIP /year production rates with electrode cermet, interconnects, and high-temperature heat treatments dominating the total cost. Integration of stacks with larger BOP equipment operating at higher pressures offers ~36% cost reduction in total facility capital cost due to an economies of physical scale effect since BOP equipment comprises >50% of facility costs. Optimized H 2 prices decrease from ~$\$$4/kgH 2 to ~$\$$2/kgH 2 for 1 GWe DCSIP facilities using $\$$0.025/kWh electricity price. All costs are reported in 2021 US dollars.

08 HYDROGEN↗
DOE OSTI2025

Cost analysis of alternative large-scale high-temperature solid oxide electrolysis hydrogen production facilities

We extend our past cost analysis of gigawatt-scale solid oxide electrolysis (SOE) facilities that produce high purity hydrogen gas from water by estimating construction and operating costs for three new alternative design cases: (1) offsite feed steam generation; (2) near-atmospheric pressure (NAP) stack; and (3) onsite electric boiler feed steam generation. Pressure effects on hydrogen electrode-(cathode-)supported SOE cell (SOEC) stack performance are estimated for the same assumed cell and stack construction and used to determine facility-wide stack capital costs for achieving a fixed H2 production at different pressures. Modular balance of plant (BOP) process equipment capital costs are estimated for each new alternative design case using our past equipment sizing, design, and cost data and scaling relationships. Furthermore, we update BOP equipment sizing and design for the NAP case using Aspen®. Vendor quotes for electric boilers are used to estimate costs for the electric boiler design case. Factory and onsite assembly and installation costs for SOEC stacks and BOP equipment are calculated using our past simplified first-principles approach. First-of-a-kind (FOAK) and N th -of-a-kind (NOAK) production maturity cost estimates are included for all results. The case with NAP stacks offers the lowest facility total capital cost (TCC, ~23% lower than base) while use of small electric boilers requires the highest TCC (~3% higher than base). H 2 production prices decrease from the base of ~$\$2.17$ /kgH 2 to ~$\$1.92$/kgH 2 for 1 GW e DC SIP facilities utilizing NAP stacks supplied by offsites steam situated in large modules and blocks for $\$0.030$/kWh e and $0.009/kWh t prices for electricity and thermal energy, respectively. We report all costs in 2021 US dollars.

Balance of plant (BOP) process equipment↗
DOE OSTI2020

Results of the International Energy Agency Bioenergy Round Robin on the Analysis of Heteroatoms in Biomass Liquefaction Oils

A round robin study evaluating the analysis of biomass liquefaction oils (BLOs) from fast pyrolysis and hydrothermal liquefaction (HTL) was performed, involving fifteen laboratories in seven countries in order to assess the current status of analytical techniques for the determination of nitrogen, sulfur, and chlorine content in BLOs and evaluate potential differences in origin (i.e. fast pyrolysis vs HTL). The BLOs were produced from a range of feedstocks including pine, mixed softwoods, forest residues, micro-algae, miscanthus, and wheat straw to cover a variety in nitrogen, sulfur, and chlorine content and speciation. Nine samples were distributed, comprised of eight separate BLOs and one blind duplicate produced by five producers. The samples were analyzed for water, carbon, hydrogen, nitrogen, sulfur, and chlorine content. No analytical test method was mandated; laboratories were encouraged to utilize whichever method they determined would be most applicable, relying on the existing body of BLO literature as a guide. The results of this round robin study are presented in this paper. The results of the carbon, hydrogen, and water measurements as reference analyses had relative standard deviations (2.9%, 3.5, and 5.6%, respectively) that were comparable to those found in past round robin studies on fast pyrolysis bio-oil. The analysis of nitrogen, sulfur, and chlorine showed higher levels of variability. Laboratories mostly chose the same method for water, carbon, hydrogen and nitrogen determination whereas there were a variety of methods chosen for sulfur and chlorine determination. The results suggest that specific analytical methods for the determination of nitrogen, sulfur, and chlorine should be further refined to ensure reproducible and accurate results for BLO analysis due to their importance on emissions, material selection, and catalyst activity.

Biomass, IEA Bioenergy, pyrolysis, hydrothermal li↗
DOE OSTI2022

Optimization of Extended-Surface PtNi Nanowire Oxygen Reduction Electrocatalysts Produced via Atomic Layer Deposition

Polymer electrolyte membrane fuel cells (PEMFCs) produce electricity with only heat and water as byproducts, but sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode and durability limitations restrict widespread commercialization, motivating the development of advanced catalysts. In this research, extended-surface platinum nickel (PtNi) nanowires (NWs) synthesized using the scalable atomic layer deposition (ALD) technique are investigated with the goal of exploring the durability benefits of high-aspect-ratio electrocatalysts and the tunability of beneficial kinetic properties. The surface and bulk composition and the structure of the PtNi NWs were investigated as a function of a series of postsynthesis modifications. The results from a combination of electron microscopy and X-ray spectroscopy characterization techniques were correlated to electrochemical performance to gain a comprehensive understanding of the structure-property-performance relationships. The robust structure of the ALD-derived NWs enabled additional postsynthesis optimization steps, which were not possible with previous-generation materials synthesized via spontaneous galvanic displacement, resulting in a catalyst with beneficial properties for catalyst kinetics as well as improved durability. Our study demonstrates potential pathways toward further improving the performance of this class of materials through optimization of bulk and surface properties of the catalyst.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2020

Pathway to Complete Energy Sector Decarbonization with Available Iridium Resources using Ultralow Loaded Water Electrolyzers

We present ultralow Ir-loaded (ULL) proton exchange membrane water electrolyzer (PEMWE) cells that can produce enough hydrogen to largely decarbonize the global natural gas, transportation, and electrical storage sectors by 2050, using only half of the annual global Ir production for PEMWE deployment. This represents a significant improvement in PEMWE's global potential, enabled by careful control of the anode catalyst layer (CL), including its mesostructure and catalyst dispersion. Using commercially relevant membranes (Nafion 117), cell materials, electrocatalysts, and fabrication techniques, we achieve at peak a 250× improvement in Ir mass activity over commercial PEMWEs. An optimal Ir loading of 0.011 mg Ir cm -2 operated at an Ir-specific power of ~100 MW kg Ir -1 at a cell potential of ~1.66 V versus RHE (85% higher heating value efficiency). Here, we further evaluate the performance limitations within the ULL regime and offer new insights and guidance in CL design relevant to the broader energy conversion field.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Codesign of an integrated metal–insulator–semiconductor photocathode for photoelectrochemical reduction of CO 2 to ethylene

Photoelectrochemical carbon-dioxide reduction (PEC CO 2 R) is a potentially attractive means for producing chemicals and fuels using sunlight, water, and carbon dioxide; however, this technology is in its infancy. To date, most studies of PEC CO 2 R have reported products containing one carbon atom (C 1 products) but the production of valuable products containing two or more carbons (C 2+ products), such as ethylene, ethanol, etc., is rarely demonstrated. Metal–semiconductor–insulator (MIS) photocathode/catalyst structures offer a promising approach for this purpose, since they integrate the functions of light absorption, charge separation, and catalysis. In this study, we have investigated a Cu/TiO 2 /p-Si photocathode/catalyst structure with the aim of establishing the effects of semiconductor–insulator interactions on the performance of the photocathode and the influence of the direction of illumination of the MIS structure on the total current density and the distribution of products formed by on the Cu catalyst. Here, we have also examined the influence of ionomer coatings deposited on the Cu surface on the total current density and the distribution of products formed. A major finding is that for a fixed Cu potential the distribution of products formed by PEC CO 2 R are the same, irrespective of the direction of illumination, and are identical to those obtained by electrochemical reduction of CO 2 (EC CO 2 R). Another important finding is that the total current density and the faradaic efficiency to ethylene are enhanced significantly by deposition of a thin bilayer of Sustainion/Nafion onto the surface of the Cu.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

A surface mechanism for O 3 production with N 2 addition in dielectric barrier discharges

Ozone, O 3 , is a strong oxidizing agent often used for water purification. O 3 is typically produced in dielectric barrier discharges (DBDs) by electron-impact dissociation of O 2 , followed by three-body association reactions between O and O 2 . Previous studies on O 3 formation in low-temperature plasma DBDs have shown that O 3 concentrations can drop to nearly zero after continued operation, termed the ozone-zero phenomenon (OZP). Including small (<4%) admixtures of N 2 can suppress this phenomenon and increase the O 3 production relative to using pure O 2 in spite of power deposition being diverted from O 2 to N 2 and the production of nitrogen oxides, N x O y . The OZP is hypothesized to occur because O 3 is destroyed on the surfaces in contact with the plasma. Including N 2 in the gas mixture enables N atoms to occupy surface sites that would otherwise participate in O 3 destruction. The effect of N 2 in ozone-producing DBDs was computationally investigated using a global plasma chemistry model. A general surface reaction mechanism is proposed to explain the increase in O 3 production with N 2 admixtures. The mechanism includes O 3 formation and destruction on the surfaces, adsorption and recombination of O and N, desorption of O 2 and N 2 , and NO x reactions. Without these reactions on the surface, the density of O 3 monotonically decreases with increasing N 2 admixture due to power absorption by N 2 leading to the formation of nitrogen oxides. With N-based surface chemistry, the concentrations of O 3 are maximum with a few tenths of percent of N 2 depending on the O 3 destruction probability on the surface. The consequences of the surface chemistry on ozone production are less than the effect of gas temperature without surface processes. An increase in the O 3 density with N-based surface chemistry occurs when the surface destruction probability of O 3 or the surface roughness was decreased.

54 ENVIRONMENTAL SCIENCES↗