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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Mediated Electrochemical Probing: A Systems-Level Tool for Redox Biology

Biology uses well-known redox mechanisms for energy harvesting (e.g., respiration), biosynthesis, and immune defense (e.g., oxidative burst), and now we know biology uses redox for systems-level communication. Currently, we have limited abilities to “eavesdrop” on this redox modality, which can be contrasted with our abilities to observe and actuate biology through its more familiar ionic electrical modality. In this Perspective, we argue that the coupling of electrochemistry with diffusible mediators (electron shuttles) provides a unique opportunity to access the redox communication modality through its electrical features. Here, we highlight previous studies showing that mediated electrochemical probing (MEP) can “communicate” with biology to acquire information and even to actuate specific biological responses (i.e., targeted gene expression). We suggest that MEP may reveal an extent of redox-based communication that has remained underappreciated in nature and that MEP could provide new technological approaches for redox biology, bioelectronics, clinical care, and environmental sciences.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Automated Redox Titrations via Interdigitated Electrode Arrays: Application to the Mediated Electron Transfer Interrogation of Charge and Rate on Electrodeposited Polymers

Mediated electron transfer (MET) plays a crucial role in energy storage and conversion technologies such as redox targeting flow batteries (RTFBs), yet its experimental investigation often requires labor-intensive and low-throughput setups. To address this, we developed a microfabricated interdigitated electrode array (IDA) platform that enables automated, high-throughput electrochemical redox titration measurement to be performed to study the MET process. Our redox titration method enables simultaneous measurement of the charge capacity and rate of MET processes on a material or surface. Automated redox titration (ART) facilitates systematic investigation of the MET process across a broad parameter space, exemplified through the study of polypyrrole (PPy) and a pyrene-4,5,9,10-tetrone azo group-based polymer (PTAP), both redox-active polymers relevant to various energy storage applications. Using PPy as a model material, 500 redox titration measurements were conducted within 50 h, varying the electrode gap widths, polymer charging potentials, voltammetric scan rates, and electrolyte concentrations. Finite-element simulations confirmed the electrochemical responses and elucidated the kinetics of the MET reactions. Our automated methodology was further tested with PTAP, revealing a surprising charging potential dependence on the rate of MET. The automation, flexibility, and scalability of our redox titration platform pave the way not only for advanced studies of MET processes relevant to RTFBs, but also with implications in the understanding of next-generation energy storage materials, molecular electrocatalysis, and biosensing.

electrochemical analysis↗
DOE OSTI2023

Soluble Iron Enhances Extracellular Electron Uptake by Shewanella oneidensis MR‐1

Abstract Extracellular electron transfer (EET) is a process that microorganisms use to reduce or oxidize external insoluble electron acceptors or donors. Much of our mechanistic understanding of this process is derived from studies of transmembrane cytochrome complexes and extracellular redox shuttles that mediate outward EET to anodes and external electron acceptors. In contrast, there are knowledge gaps concerning the reverse process of inward EET from external electron donors to cells. Here, we describe a role for soluble iron (exogenous FeCl 2 ) in enhancing EET from cathodes to the model EET bacterium Shewanella oneidensis MR‐1, with fumarate serving as the intracellular electron acceptor. This iron concentration‐dependent electron uptake was eradicated upon addition of an iron chelator and occurred only in the presence of fumarate reductase, confirming an electron pathway from cathodes to this periplasmic enzyme. Moreover, S. oneidensis mutants lacking specific outer membrane and periplasmic cytochromes exhibited significantly decreased current levels relative to wild‐type. These results indicate that soluble iron can function as an electron carrier to the EET machinery of S. oneidensis .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Extracellular Charge Transport in Microbial Redox Chains: Linking the Living and Non-Living Worlds

The fundamental process of electron transfer (ET) within and between molecules dictates all biological energy conversion strategies, including respiration and photosynthesis. This project resulted in a comprehensive physics-based understanding of the mechanisms and limits of redox networks that mediate and regulate electron transport through microbial metabolic pathways, with special emphasis on environmental microbes that can acquire energy by catalyzing anodic or cathodic reactions on solid-state electrodes (extracellular electron transfer, or EET). By performing electron transfer to/from electrodes, such microbes may be used as biocatalysts for converting the energy stored in diverse chemical fuels to electricity, or vice versa (microbial electrosynthesis), in renewable energy technologies.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Interactive Materials for Bidirectional Redox-Based Communication

Emerging research indicates that biology routinely uses diffusible redox-active molecules to mediate communication that can span biological systems (e.g., nervous and immune) and even kingdoms (e.g., a microbiome and its plant/animal host). This redox modality also provides new opportunities to create interactive materials that can communicate with living systems. Here in this paper, it is reported that the fabrication of a redox-active hydrogel film can autonomously synthesize a H 2 O 2 signaling molecule for communication with a bacterial population. Specifically, a catechol-conjugated/crosslinked 4-armed thiolated poly(ethylene glycol) hydrogel film is electrochemically fabricated in which the added catechol moieties confer redox activity: the film can accept electrons from biological reductants (e.g., ascorbate) and donate electrons to O 2 to generate H 2 O 2 . Electron-transfer from an Escherichia coli culture poises this film to generate the H 2 O 2 signaling molecule that can induce bacterial gene expression from a redox-responsive operon. Overall, this work demonstrates that catecholic materials can participate in redox-based interactions that elicit specific biological responses, and also suggests the possibility that natural phenolics may be a ubiquitous biological example of interactive materials.

electrobiofabrication↗
DOE OSTI2020

Electroenzymatic Nitrogen Fixation Using a MoFe Protein System Immobilized in an Organic Redox Polymer

Abstract We report an organic redox‐polymer‐based electroenzymatic nitrogen fixation system using a metal‐free redox polymer, namely neutral‐red‐modified poly(glycidyl methacrylate‐ co ‐methylmethacrylate‐ co‐ poly(ethyleneglycol)methacrylate) with a low redox potential of −0.58 V vs. SCE. The stable and efficient electric wiring of nitrogenase within the redox polymer matrix enables mediated bioelectrocatalysis of N 3 − , NO 2 − and N 2 to NH 3 catalyzed by the MoFe protein via the polymer‐bound redox moieties distributed in the polymer matrix in the absence of the Fe protein. Bulk bioelectrosynthetic experiments produced 209±30 nmol NH 3 nmol MoFe −1 h −1 from N 2 reduction. 15 N 2 labeling experiments and NMR analysis were performed to confirm biosynthetic N 2 reduction to NH 3 .

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2024

Catalyst design for small molecule activation of energy consequence

This project targets the conversion of ubiquitous small molecules (e.g. NO, CO, H 2 O) into viable precursors to synthetic fuels. Current state of the art catalyst design has not directly targeted transition metal complexes capable of mediating the multi-electron redox processes necessary to reduce the overpotential (energy loss) required achieve efficient activation of small molecule substrates. In this vein, a new strategy has been developed for the assembly of polynuclear architectures; allowing for the construction of tunable polymetallic centers that assemble easily within a pre-organized template (conferring stability, selectivity and tunability) that can effect multi-electron redox processes for reactions. Catalyst development has commenced with the following target design elements: (1) catalysts featuring multiple transition metal ions in the same reaction space to greatly expand accessible molecular redox capabilities; (2) catalysts are assembled in a polynucleating ligand framework that permits control over the cluster morphology as well as the local steric and electronic environment of the transition metal ions within the cluster. The high-tunability of the catalyst composition (metal content) and geometric flexibility has permitted a rigorous assessment of electronic-structure-to-function relationship to be developed, further guiding synthetic efforts to realize more potent catalysts. The numerous permutations possible showcase the high degree of generality to this approach with many synthetic handles to tune redox and reaction chemistry. Trinuclear complexes have been synthesized featuring homo- and hetero-trinuclear cores featuring a variety of first row transition metal ions (Cr→Ni). The molecular clusters have been shown to successfully mediate multi-electron redox processes in a cooperative fashion without requiring strong chemical reductants or oxidants. The reactive molecular complexes are being utilized to activate and breakdown the robust bonds within typical waste stream small molecules (e.g., greenhouse gases) and convert them into value-added commodity chemicals. Ultimately, the catalysts developed by this approach will be required to convert energy acquired via renewable resources (e.g., solar or wind) into synthetic fuels as an energy storage mechanism.

10 SYNTHETIC FUELS↗
DOE OSTI2022

The role of Co valence in charge transport in the entropy‐stabilized oxide (Mg 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 )O

Abstract Many of the studies on the entropy‐stabilized oxide (Mg 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 )O have been heavily application‐based. Previous works have studied effects of cation stoichiometry on the entropy‐driven reaction to form a single phase, but a fundamental exploration of the effects of anion stoichiometry and/or redox chemistry on electrical properties is lacking. Using near‐edge X‐ray absorption fine structure (NEXAFS) and electrical measurements, we show that oxidizing thin film samples of (Mg 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 )O affects primarily the valence of Co, leaving the other cations in this high‐entropy system unchanged. This oxidation increases electrical conduction in these thin films, which occurs via small polaron hopping mediated by the Co valence shift from 2+ to a mixed 2+/3+ state. In parallel, we show that bulk samples sintered in an oxygen‐rich atmosphere have a lower activation energy for electrical conduction than those equilibrated in a nitrogen (reducing) atmosphere. Combining feasible defect compensation scenarios with electrical impedance measurements and NEXAFS data, we propose a self‐consistent interpretation of Co redox‐mediated small polaron conduction as the dominant method of charge transfer in this system.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Role of redox-active biochar with distinctive electrochemical properties to promote methane production in anaerobic digestion of waste activated sludge

Biochar has been reported as an effective additive to improve methane production during anaerobic digestion (AD). However, the mechanism for such a stimulatory impact remains unclear. Here we investigated the capability of three pyrolytic biochars with distinctive electrochemical properties (BC300, BC500, BC700) to promote methanogenic performance of anaerobic digesters treating waste activated sludge (WAS). The cumulative methane production and the maximum methane production rate were increased by 46.9% and 181.6%, respectively, with BC300 amendment. By characterizing the electrochemical properties of biochar, our research team found out that methane production in AD of sludge was positively correlated to biochar’s electron-donating capacity (EDC) rather than its bulk electrical conductivity. These results indicate that the electron transfer mediated by the redox-active functional groups may prevail over the direct electron migration as the predominant mechanism to facilitate interspecies electron transfer in syntrophic communities for enhanced methanogenesis. Microbial community analysis suggests that biochar enriched Methanosarcina and Methanobacterium. Overall, this study shows that functional groups-mediated electron transfer contributes greatly to the improved methane production in WAS digester with biochar amendment.

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

Allosteric control of electron transfer in nitrogenase and nitrogenase-like enzymes (Final Report)

More than a third of all known proteins to date are either oxidoreductases or metalloproteins. The diversity of metal cofactors and redox centers in these proteins make them attractive candidates for engineering protein-based biocatalysts, biosensors, and biofuel cells, among other necessary tools for the bioeconomy. Many of these enzymes function as large multi-subunit complexes arranged as symmetric or asymmetric assemblies, and the purpose of this architecture is unclear. The goal of the project was to address this fundamental question by investigating the mechanism of action of two oxidoreductases: Nitrogenase and DPOR (Dark-Operative Protochlorophyllide Oxidoreductase, a nitrogenase-like oxidoreductase). Nitrogenase and DPOR play key roles in nitrogen fixation and photosynthesis, processes essential to sustaining life. Both proteins are arranged as two symmetrical halves with each half capable of substrate reduction. For more than half a century, substrate reduction by nitrogenase has been presumed to occur independently within the two identical halves. Funded by this DOE grant we have now shown that both nitrogenase and DPOR function asymmetrically. Electron transfer in one half suppresses activity in the other. Thus, we have demonstrated that the two halves do not function in an independent manner; rather, catalytic events in one-half allosterically suppress activity and electron transfer (ET) in the other. This alternating-site mechanism has significant implications on our current understanding of substrate reduction by these enzymes and offers a new mechanistic paradigm for the reactions they catalyze. Our work now provides a mechanistic map of the how the two symmetric catalytic halves work together to establish and maintain the sequential-site mechanism through multiple ET cycles to achieve substrate reduction. There is substantive need for bio-inspired tools that enable reduction of nitrogen and other substrates, as well as photosynthesis, for energy and food production. Understanding the workings of enzymes like nitrogenase and DPOR that mediate multi-electron redox chemistry is vital for designing such synthetic tools. The timing of our research coincides with the biotechnological breakthrough of light-driven artificial N2 reduction by nitrogenase, achieved using the native enzyme with both halves arranged in a mirror-like architecture as catalyst. Together with such discoveries, our research now reveal unknown facets of the reaction mechanism and hold promise for designing more effective catalysts.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Multielectron Bond Cleavage Processes Enabled by Redox-Responsive Phosphinimide Ligands

The activation of small molecules via multielectron redox processes offers promise in mediating difficult transformations related to energy conversion processes. While molecular systems that engage in one- and two-electron redox processes are widespread, those that participate in the direct transfer of four or more electrons to small molecules are very rare. To that end, we report a mononuclear Cr II complex competent for the 4-electron reduction of dioxygen (O 2 ) and nitrosoarenes. These systems additionally engage in facile two-electron group transfer reactivity, including O atom excision and nitrene transfer. Structural, spectroscopic, and computational studies support bond activation processes that intimately occur at a mononuclear chromium(phosphinimide) center and highlight the unusual structural responsiveness of the phosphinimides in stabilizing a range of metal redox states.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Impact of Urban Pollution on Organic-Mediated New-Particle Formation and Particle Number Concentration in the Amazon Rainforest

A major challenge in assessing the impact of aerosols on climate change is to understand how human activities change aerosol loading and properties relative to the pristine-preindustrial baseline. Here we combine chemical transport simulation and field measurements to investigate the effect of anthropogenic pollution from an isolated metropolis on particle number concentration over the preindustrial-like Amazon rainforest through various new-particle formation (NPF) mechanisms and primary particle emissions. To represent organic-mediated NPF, we employ a state-of-the-art model that systematically simulates the formation chemistry and thermodynamics of extremely low volatility organic compounds as well as their roles in NPF processes, and further update the model to improve organic NPF simulations under human-influenced conditions. Results show that urban pollution from the metropolis increases particle number concentration by a factor of 5–25 over the downwind region (within 200 km from city center) compared to background conditions. Overall, our model indicates that NPF contributes over 70% of the total particle number in the downwind region except immediately adjacent to the sources. Among different NPF mechanisms, the ternary NPF involving organics and sulfuric acid overwhelmingly dominates. The improved understanding of particle formation mechanisms will help better quantify anthropogenic aerosol forcing from pristine-preindustrial times to present day.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

New Materials for Photoelectrochemical Energy Conversion

This review concerns light-to-chemical energy conversion, focusing on approaches that could be driven by terrestrial sunlight to produce hydrogen and/or reduce carbon dioxide. Recent advances in photocatalytic (PC) and photoelectrocatalytic (PEC) materials are covered. In both approaches, the electron-hole pairs that are created by photon absorption must travel in specific directions to the sites that mediate multielectron bond making/breaking redox reactions. Thermodynamic requirements for materials stability are described, although some recently discovered materials appear to be exceptions. For PC materials, the importance of rate matching between reduction and oxidation processes and the mass transfer of intermediates and products is emphasized. Surprisingly, metal sulfides appear to be promising for PC carbon dioxide reduction. For PEC materials, recent work elucidating the elementary step mechanism for oxygen evolution on metal oxides and the discovery of chalcogen-based photocathode materials capable of sustained light-driven CO 2 reduction are discussed.

energy conversion↗
DOE OSTI2026

Manganese Oxidation during Vegetation Burning

Redox recycling of manganese (Mn) plays a key role in organic matter decomposition and nutrient cycling in terrestrial vegetated ecosystems, and it is expected to be changed by fires. This study revealed how Mn is oxidized during vegetation burning, by characterizing the chemical speciation of Mn in fire ash from wildland fires and laboratory burning and evaluating the factors governing its average oxidation state (AOS) and speciation. Manganese in wildland fire ash from different ecosystems showed variable AOS that ranges from 2.5 to 3.3. Laboratory burning experiments showed that Mn oxidation was primarily controlled by fire thermal intensity (temperature × duration) and burning completeness. As heating time increased from 5 min to 5 h at 550 and 700 °C, Mn AOS in the lab-burned vegetation ash increased from 2.7 to 4.0 and the oxidation rate was faster at higher temperature. Diverse Mn species can present in wildland fire ash and differ structurally from biogenic Mn oxides. The oxidized Mn species enable fire ash to mediate oxidative degradation of catechol, demonstrating its potential in mediating organic matter decomposition. This study revealed a new paradigm of Mn redox recycling, as compared to the microbe-mediated Mn redox cycling in the absence of fires.

36 MATERIALS SCIENCE↗