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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Emergent Degradation Phenomena Demonstrated on Resilient, Flexible, and Scalable Integrated Photoelectrochemical Cells

Photoelectrochemical (PEC) water splitting provides a pathway to generate sustainable clean fuels using the two most abundant resources on Earth: sunlight and water. Currently, most of the successful models of PEC cells are still fabricated on small scales near 1 cm 2 , which largely limits the mass deployment of solar-fuel production. Here, the scale-up to 8 cm 2 of an integrated PEC (IPEC) device is demonstrated and its performance compared to a 1 cm 2 IPEC cell, using state-of-the-art iridium and platinum catalysts with III–V photoabsorbers. The initial photocurrents at 1 sun are 8 and 7 mA cm -2 with degradation rates of 0.60 and 0.47 mA cm -2 day -1 , during unbiased operation for the 1 and 8 cm 2 devices, respectively. Additionally, evaluating under outdoor and indoor conditions at two U.S. National Laboratories reveals similar results, evidencing the reproducibility of this design's performance. Furthermore, the emerging degradation mechanisms during scale-up are investigated and the knowledge gained from this work will provide feedback to the broader community, since PEC device durability is a limiting factor in its potential future deployment.

25 ENERGY STORAGE↗
DOE OSTI2020

Water Splitting: Emergent Degradation Phenomena Demonstrated on Resilient, Flexible, and Scalable Integrated Photoelectrochemical Cells (Adv. Energy Mater. 48/2020)

We report Photoelectrochemical (PEC) water splitting provides a pathway to generate sustainable clean fuels using the two most abundant resources on Earth: sunlight and water. Currently, most of the successful models of PEC cells are still fabricated on small scales near 1 cm 2 , which largely limits the mass deployment of solar-fuel production. Here, the scale-up to 8 cm 2 of an integrated PEC (IPEC) device is demonstrated and its performance compared to a 1 cm 2 IPEC cell, using state-of-the-art iridium and platinum catalysts with III-V photoabsorbers. The initial photocurrents at 1 sun were 8 and 7 mA cm -2 with degradation rates of 0.60 and 0.47 mA cm -2 day -1 , during unbiased operation for the 1 and 8 cm 2 devices, respectively. Evaluating under outdoor and indoor conditions at two US National Laboratories revealed similar results, evidencing the reproducibility of this design’s performance. Furthermore, the emerging degradation mechanisms during scale-up are investigated and the knowledge gained from this work will provide feedback to the broader community, since PEC device durability is a limiting factor in its potential future deployment.

25 ENERGY STORAGE↗
DOE OSTI2023

Technoeconomic Model and Pathway to <$2/kg Green Hydrogen Using Integrated Halide Perovskite Photoelectrochemical Cells

The cost of gray hydrogen produced via fossil fuel-based steam-methane reforming has led the U.S. Department of Energy to specify <$\$$2/kg H 2 as a target for commercially competitive green hydrogen generation methods. Integrated photoelectrochemical cells have been proposed as a solar-to-hydrogen conversion technology. In this paper we describe a technoeconomically feasible pathway to reaching <$\$$2/kg green H 2 using integrated photoelectrochemical cells with halide perovskite photoabsorbers, low-cost conductive barriers, and low precious metal-content catalysts in an aqueous, membrane-separated cell. A base-case solar-to-hydrogen conversion efficiency of 20%, stable lifetime of 10 years, and a combined electrocatalyst-plus-panel cost of $\$$50/m 2 enabled a levelized cost of hydrogen of $\$$2.43/kg, which dropped below $\$$2/kg with improved performance metrics including material cost, improvements in process design, or subsidies. We relate these metrics to lab-scale reports to recommend best research practices for scientists and funding agencies working at this intersection of photovoltaics, electrocatalysis, and surface science.

$1/kg↗
DOE OSTI2023

Integrated halide perovskite photoelectrochemical cells with solar-driven water-splitting efficiency of 20.8%

Abstract Achieving high solar-to-hydrogen (STH) efficiency concomitant with long-term durability using low-cost, scalable photo-absorbers is a long-standing challenge. Here we report the design and fabrication of a conductive adhesive-barrier (CAB) that translates >99% of photoelectric power to chemical reactions. The CAB enables halide perovskite-based photoelectrochemical cells with two different architectures that exhibit record STH efficiencies. The first, a co-planar photocathode-photoanode architecture, achieved an STH efficiency of 13.4% and 16.3 h to t 60 , solely limited by the hygroscopic hole transport layer in the n-i-p device. The second was formed using a monolithic stacked silicon-perovskite tandem, with a peak STH efficiency of 20.8% and 102 h of continuous operation before t 60 under AM 1.5G illumination. These advances will lead to efficient, durable, and low-cost solar-driven water-splitting technology with multifunctional barriers.

08 HYDROGEN↗
DOE OSTI2023

Platinum group metal-free (PGM-free) integrated tandem junction photoelectrochemical (PEC) water splitting devices (Final Technical Report)

This project involves using solar light, a photoabsorber, and a catalyst to split water and produce hydrogen. The Department of Energy (DOE) targets for integrated photoelectrochemical (PEC) cells emphasize cost (electrode cost < $200/m 2 ), performance (> 15% solar to hydrogen (STH) efficiency), and stability (> 6 months electrode lifetime), but most approaches skew toward one specific metric. This project exploited interfacial integration of platinum group metal-free (PGM-free) catalysts on the high performance and high value tandem solar cells to attain or exceed the DOE benchmark STH energy conversion efficiency and durability. This was investigated in two thrusts by developing two PEC devices for direct comparison: the first is a high-performance monolithic device based on state-of-the-art GaInP 2 /GaAs tandem solar cells developed at National Renewable Energy Laboratory (NREL), and the second is a high-value device based on earth-abundant wide band gap photoabsorber materials including oxynitride and hybrid organic-inorganic perovskite (HOIP) coupled with commercial narrow band gap silicon (Si). Both these devices were paired with electrocatalysts developed for this purpose at Rutgers University by adapting them to thin films on the photoabsorbers. These catalysts are based on the hydrogen evolution reaction (HER) catalysts (Ni 5 P 4 ), oxygen evolution reaction (OER) catalysts (LiCo 2 O 4 ) previously developed at Rutgers for high-efficiency electrolyzers. For using the high-performance tandem solar cell and Ni 5 P 4 catalysts, we achieved a durability of > 200 h at a STH efficiency of > 10%. For using the high-value wide band gap single junction solar cells on n + Si, we achieved 0.73 mA/cm 2 at 1.23V vs reversible hydrogen electrode (RHE) and -15.9 mA/cm 2 at 0V vs RHE using the oxynitride- and HOIP-based photoelectrodes, respectively. After comparing their photocurrent densities, we down selected the HOIP photoabsorber to couple Si for fabrication of a tandem photocathode. However, due to the COVID-19 pandemic, both the laboratories at Rutgers and NREL were locked down for three months and reopened only partially in 2020. The HOIP/Si tandem photocathode using robust nickel phosphide thin film catalysts cannot be developed within the project period, which is expected to achieve a STH efficiency of > 20%. Also, the low-cost LiCo 2 O 4 OER catalysts need to replace the benchmark IrO 2 for evaluation. Finally, techonomic analysis of full high-performance and high-value integrated PEC devices needs to be carried out for comparison in terms of cost.

08 HYDROGEN↗
DOE OSTI2023

Modular Solar-to-Fuel Electrolysis at Low Cell Potentials Enabled by Glycerol Electrooxidation and a Bipolar Membrane Separator

Solar fuel generation through water electrolysis or electrochemical CO 2 reduction is thermodynamically limited when paired with the oxygen evolution reaction (OER). The glycerol electrooxidation reaction (GEOR) is an alternative anodic reaction with lower anodic electrochemical potential that utilizes a renewable coproduct produced during biodiesel synthesis. We show that GEOR on a Au-Pt-Bi ternary metal electrocatalyst in a model alkaline crude glycerol solution can provide significant cell potential reductions even when paired to reduction reactions in seawater and acidic catholytes via a bipolar membrane (BPM). We showed that the combination of GEOR electrooxidation and a BPM separator lowers the total cell potential by 1 V at an electrolysis current of 10.0 mA cm -2 versus to an anode performing OER when paired with hydrogen evolution and CO 2 reduction cathodes. The observed voltage reduction was steady for periods of up to 80 hours, with minimal glycerol crossover observed through the membrane. Furthermore, these results motivate new, high-performance cell designs for photoelectrochemical solar fuels integrated systems based on glycerol electrooxidation.

25 ENERGY STORAGE↗
DOE OSTI2024

Comparative Study on the Photoelectrochemical Hydrogen Production from the Layout Optimization in a Unit Cell

Solar-driven water splitting is achieved by connecting photovoltaics with electrolysis. Recently, integrated approaches of the two configurations for photoelectrochemical reactions have shown great potential in a combined unit, but strategies to address further material and cell development face significant scientific challenges. Here, in this work, we present an experimental demonstration of photoelectrochemical (PEC) unit-cells with efficient separate dual compartments for oxygen evolution and hydrogen evolution reactions. The design and fabrication of cell architectures with various degrees of integration are investigated efficient and sustainable PEC processes. The effect of the nanostructured silicon (Si) photoelectrodes, including the adoption of layer architectures, surface protection layer deposition, and membrane electrode assembly is further studied to optimize the design parameters of the PEC unit-cells. This developed PEC cell with the Si photocathode achieved a photocurrent density of -4.8 mA cm –2 at -2.0 V cell and -2.87 mA cm –2 at -1.6 V cell . It clearly provides a critical milestone for unbiased solar water splitting. Practical solar to hydrogen (STH) can be directly estimated in investigating PEC performance in this unit-cell as assembled with a solar cell. It is a significantly meaningful step forward in practical solar fuel production.

08 HYDROGEN↗
DOE OSTI2022

Creating Functional Oxynitride–Silicon Interfaces and SrNbO 2 N Thin Films for Photoelectrochemical Applications

Photoelectrochemical performance dependence upon absorption length, carrier diffusion length, and surface area of an oxynitride photoabsorber is investigated. How best to fabricate optical-quality thin films of bandgap-tunable oxynitrides is also discussed. We targeted the stoichiometric compound SrNbO 2 N as an optimal wide-bandgap photoabsorber (1.9 eV) for use with silicon (1.1 eV) in a tandem structure photoelectrochemical cell. Preparation of perovskite oxynitrides at high-temperature as isolated powders is often straightforward, but it is difficult to integrate them as thin films in tandem junction devices with low-temperature materials. Here we develop the first method to prepare optical-quality SrNbO 2 N thin-films of tunable thickness and roughness on single-crystal silicon substrate. This achievement required an interfacial layer of ultra-thin TaN to be used as a barrier to reduce the inter-diffusion of silicon and oxygen during oxynitride syn-thesis. We produced a variety of SrNbO 2 N film thicknesses (20-440 nm) on n + -Si(100) surfaces. Roughness factor (0.14-21) scaled with thickness. The intrinsic photoelectrochemical activity of these devices was evaluated using a low-barrier sacrificial electron donor. Photocurrent density and photovoltage revealed a significant (and non-linear) dependence on film thickness and roughness. Furthermore, absorption length, carrier diffusion length, and surface area were each found to play key roles. Balancing these is required for optimally performing devices.

08 HYDROGEN↗
DOE OSTI2021

Integrating computation and experiment to investigate photoelectrodes for solar water splitting at the microscopic scale.

CONSPECTUS: Photoelectrochemical water-splitting is a promising and sustainable way to store the energy of the sun in chemical bonds and use it to produce hydrogen gas, a clean fuel. The key components in photoelectrochemical cells (PECs) are photoelectrodes, including a photocathode that reduces water to hydrogen gas and a photoanode that oxidizes water to oxygen gas. Materials used in photoelectrodes for PECs must effectively absorb sunlight, yield photogenerated carriers, and exhibit electronic properties that enable the efficient shuttling of carriers to the surface to participate in relevant water-splitting reactions. Discovering and understanding the key characteristics of optimal photoelectrode materials is paramount to the realization of PEC technologies. Oxide-based photoelectrodes can satisfy many of these materials requirements, including stability in aqueous environments, band edges with reasonable alignment with the redox potentials for water splitting, and ease of synthesis. However, oxide photoelectrodes generally suffer from poor charge transport properties and considerable bulk electron-hole separation, and they have relatively large band gaps. Numerous strategies have been proposed to improve these aspects and understand how these improvements are reflected in the photoelectrochemical performance. Unfortunately, the structural and compositional complexity of multinary oxides accompanied by the inherent complexity of photoelectrochemical processes makes it challenging to understand the individual effects of composition, structure, and defects in the bulk and on the surface on a material's photoelectrochemical properties. The integration of experiment and theory has great potential to increase our atomic-level understanding of structure-composition-property relationships in oxide photoelectrodes. In this Account, we describe how integrating experiment and theory is beneficial for achieving scientific insights at the microscopic scale. We highlight studies focused on understanding the role of (i) bulk composition via solid-state solutions, intercalation, and comparison with isoelectronic compounds, (ii) dopants for both the anion and cation and their interactions with oxygen vacancies, and (iii) surface/interface structure in the photocurrent generation and photoelectrochemical performance in oxide photoelectrodes. In each instance, we outline strategies and considerations for integrating experiment and theory and describe how this integration led to valuable insights and new directions in uncovering structure-composition-property relationships. Our aim is to demonstrate the unique value of combining experiment and theory in studying photoelectrodes and to encourage the continued effort to bring experiment and theory in closer step with each other.

Wang, Wennie↗
DOE OSTI2024

Hydrogen and its Vital Role in a Clean Energy Future

Large-scale, low -cost hydrogen production can enable an economically competitive, secure, and environmentally beneficial future energy system across multiple sectors. Furthermore, clean hydrogen can address specific sectors that are hard to decarbonize (e.g., heavy-duty trucking, load-following electricity, iron, steel, and cement) and can help the U.S. meet the net zero carbon goal by 2050. To achieve this goal, tens of millions of metric tons of clean, reliable, and affordable hydrogen will be needed annually1. In 2021, the Hydrogen Energy Earthshot was launched, and its goal is to reduce the cost of clean hydrogen to $1 per $1 kilogram in 1 decade (1 1 1) 2. One very promising pathway for large-scale hydrogen production is water splitting. Water splitting technologies range from commercial technologies such as electrolyzers to approaches that are at a much earlier stage of development, such as photoelectrochemical (PEC) and thermochemical (TCH) processes. All these water splitting pathways offer diverse benefits in energy storage, grid services, and cross-sector emissions reductions while taking advantage of the diverse domestic resources. However, critical materials-, component- and system-level challenges must be addressed to improve efficiency and durability and reduce cost. To address these barriers and move these promising and high impact technologies forward, the HydroGEN Advanced Water Splitting Materials (AWSM) and the H2 from the Next-generation of Electrolyzers of Water (H2NEW) consortia were formed and supported by the Department of Energy (DOE) EERE Hydrogen and Fuel Cell Technologies Office (HFTO). HydroGEN (https://www.energy.gov/eere/h2awsm/) consortium, established in 2016, is an Energy Materials Network (EMN) that aims to accelerate the materials R&D of low technology readiness level (TRL) advanced water splitting (AWS) technologies. The consortium comprises five core national laboratories and focuses on four early-stage AWS pathways: alkaline exchange membrane (AEM) electrolysis, proton conducting solid oxide electrolysis (p-SOEC), photoelectrochemical, and thermochemical water splitting. Liquid alkaline and PEM electrolyzers are already commercial and significant advancements in oxygen conducting solid oxide electrolysis cells (o-SOECs) have been realized. Yet, these systems are still too expensive and not sufficiently durable for wide-scale commercialization. To enable high-volume manufacturing of affordable, durable, efficient electrolyzers, H2NEW (https://h2new.energy.gov/), another multi-lab consortium, was established in 2020. This comprehensive, concerted effort is focused on overcoming barriers related to components and materials integration and scale-up to achieve performance, durability, with an initial focus to achieve $2/kg H2 by 2026.

AEM↗
DOE OSTI2022

Design and characterization of surface molecular assemblies for the preparation of solar fuels

A key issue in solar energy conversion is the utilization of solar energy for the preparation of solar fuels. In this area, artificial photosynthesis offers promising approaches for the conversion of H 2 O and CO 2 into usable solar fuels. This review highlights both the design and characterization of surface molecular assemblies for the preparation of solar fuels. It includes mechanistic summaries of the details of the underlying surface chemical reactions including water oxidation and proton/water reduction. The surface mechanisms are shown to integrate molecular reactivity with surface electron transfer in integrated assemblies that lead to impressive efficiencies for water oxidation and proton or CO 2 reduction.

catalysts and catalysis↗
DOE OSTI2023

Redox‐Functionalized Semiconductor Interfaces for Photoelectrochemical Separations

Redox-mediated electrosorption is a promising platform for selective electrochemical (EC) separations, due to its molecular selectivity, high uptake, and tunability for target ions. However, the electrical energy required is mainly generated by non-renewable energy sources, which limits its sustainability and overall impact to decarbonization. Here, a redox-mediated photoelectrochemical (PEC) separation process using polyvinyl ferrocene functionalized TiO 2 nanorod electrodes is proposed, which integrates direct solar energy as a driver for the selective electrosorption. The photoelectrochemically-driven oxidation and reduction with both homogeneous and heterogeneous ferrocene-systems is investigated to establish the underlying mechanism. The PEC system can separate heavy metal oxyanions at lower voltages or even without electrical energy. At 0.3 V versus SCE, a 124 mg g −1 uptake for Mo is achieved, which is comparable to the performance of EC cells at 0.75 V versus SCE. Thus, PEC systems not only can generate energy for spontaneous redox-separations, but also can reduce electrical energy consumption by 51.4% compared to EC cells for separation processes when coupled with an external electrical energy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Semi-monolithic Integration of All-Chalcopyrite Multijunction Solar Conversion Devices via Thin-Film Bonding and Exfoliation

Here we report on a semi-monolithic integration method to circumvent processing incompatibility between materials of dissimilar classes and combine them into multijunction devices for photovoltaic and photoelectrochemical applications. Proof-of-concept all-chalcopyrite tandems were obtained by consecutive transfer of fully integrated unpatterned 1.85 eV CuGa 3 Se 5 and 1.13 eV CuInGaSe 2 PV stacks from their Mo/soda lime glass substrates onto a new single host substrate. This transfer approach consists of two key steps: (1) bonding of the solar stack (face down) onto a handle (e.g., SnO 2 :F, FTO) using a transparent conductive composite and (2) delamination of the solar stack at the chalcopyrite/Mo interface by employing a wedge-based exfoliation technique. Upon transfer onto FTO, a CuGa 3 Se 5 champion device demonstrated near-coincident photocurrent density-voltage characteristic with a baseline measurement. Then, the exfoliated CuGa 3 Se 5 single-junction stack transferred onto FTO served as the new host onto which a second fully processed CuInGaSe 2 stack was bonded (face down) onto and liberated from its Mo/SLG substrate, leading to a complete transfer of both sub-cells onto one FTO substrate. A champion semi-monolithic tandem device exhibited a power conversion efficiency of 5.04% with an open-circuit voltage, a short-circuit current density, and a fill factor of 1.24 V, 7.19 mA/cm 2 , and 56.7%, respectively. This first-time demonstration of a fully operational semi-monolithic device provides a new avenue to combine thermally, mechanically, and/or chemically incompatible thin-film material classes into tandem photovoltaic and photoelectrochemical devices while maintaining state-of-the-art sub-cell processing.

14 SOLAR ENERGY↗
DOE OSTI2024

Low‐Temperature Synthesis of Stable CaZn 2 P 2 Zintl Phosphide Thin Films as Candidate Top Absorbers

Abstract The development of tandem photovoltaics and photoelectrochemical solar cells requires new absorber materials with bandgaps in the range of ≈1.5–2.3 eV, for use in the top cell paired with a narrower‐gap bottom cell. An outstanding challenge is finding materials with suitable optoelectronic and defect properties, good operational stability, and synthesis conditions that preserve underlying device layers. This study demonstrates the Zintl phosphide compound CaZn 2 P 2 as a compelling candidate semiconductor for these applications. Phase‐pure, ≈500 nm‐thick CaZn 2 P 2 thin films are prepared using a scalable reactive sputter deposition process at growth temperatures as low as 100 °C, which is desirable for device integration. Ultraviolet‐visible spectroscopy shows that CaZn 2 P 2 films exhibit an optical absorptivity of ≈10 4 cm −1 at ≈1.95 eV direct bandgap. Room‐temperature photoluminescence (PL) measurements show near‐band‐edge optical emission, and time‐resolved microwave conductivity (TRMC) measurements indicate a photoexcited carrier lifetime of ≈30 ns. CaZn 2 P 2 is highly stable in both ambient conditions and moisture, as evidenced by PL and TRMC measurements. Experimental data are supported by first‐principles calculations, which indicate the absence of low‐formation‐energy, deep intrinsic defects. Overall, this study shall motivate future work integrating this potential top cell absorber material into tandem solar cells.

14 SOLAR ENERGY↗
DOE OSTI2023

Photoelectrochemical and Photovoltaic Performance of As-deposited Ink-based CuInS 2 Heterojunction Thin Film

In this report, we demonstrate low-temperature ink-based fabrication of CuInS 2 -based photoelectrodes for hydrogen production capable of producing photocurrent densities as high as 8.8mA.cm -2 . In this process, molecular ink made of metal chlorides and thiourea dissolved in methanol was spin coated onto Mo-coated soda lime glass substrates. Samples were then placed on a hot plate (sample surface temperature: 250°C) to induce CuInS 2 formation and remove the solvent and by-products. No further processing, such as high temperature sulfurization, was performed. Further, the CuInS 2 films were then integrated as photocathode for hydrogen evolution by photoelectrodeposition of Pt nanoparticles. Photocurrent density of 0.4mA.cm -2 at 0V vs. RHE was detected from such electrodes. However, samples coated with CdS/ZnO/ITO overlayers forming heterojunction prior to Pt deposition exhibited significant improvement of the photocurrent density, reaching 8.8mA.cm -2 at 0V vs. RHE, highlighting the improved charge transfer by the p-n junction formed at the CuInS 2 /CdS interface. The charge transfer resistance of the CuInS 2 /CdS/ZnO/ITO-Pt photoelectrode was almost 5 times lower than that of the CuInS 2 -Pt photoelectrode as revealed by electrochemical impedance spectroscopy analysis. In addition, the onset potential was shifted by ca. 0.45V toward the anodic direction, reaching 0.75V vs. RHE. Solar cell made of identical structure (Mo/CuInS 2 /CdS/ZnO/ITO) showed power conversion efficiency of 2.1% with short-circuit photocurrent density and open circuit voltage of 7.4mA.cm -2 and 820mV, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗