Fuel and oxygen harvesting from Martian regolithic brine

Bridging Place-Based Astrobiology Education with Genomics, Including Descriptions of Three Novel Bacterial Species Isolated from Mars Analog Sites of Cultural Relevance

Democratizing genomic data science, including bioinformatics, can diversify the STEM workforce and may, in turn, bring new perspectives into the space sciences. In this respect, the development of education and research programs that bridge genome science with "place" and world-views specific to a given region are valuable for Indigenous students and educators. Through a multi-institutional collaboration, we developed an ongoing education program and model that includes Illumina and Oxford Nanopore sequencing, free bioinformatic platforms, and teacher training workshops to address our research and education goals through a place-based science education lens. High school students and researchers cultivated, sequenced, assembled, and annotated the genomes of 13 bacteria from Mars analog sites with cultural relevance, 10 of which were novel species. Students, teachers, and community members assisted with the discovery of new, potentially chemolithotrophic bacteria relevant to astrobiology. This joint education-research program also led to the discovery of species from Mars analog sites capable of producing N-acyl homoserine lactones, which are quorum-sensing molecules used in bacterial communication. Whole genome sequencing was completed in high school classrooms, and connected students to funded space research, increased research output, and provided culturally relevant, place-based science education, with participants naming three novel species described here. Students at St. Andrew's School (Honolulu, Hawai'i) proposed the name Bradyrhizobium prioritasuperba for the type strain, BL16AT, of the new species (DSM 112479T = NCTC 14602T). The nonprofit organization Kauluakalana proposed the name Brenneria ulupoensis for the type strain, K61T, of the new species (DSM 116657T = LMG = 33184T), and Hawai'i Baptist Academy students proposed the name Paraflavitalea speifideiaquila for the type strain, BL16ET, of the new species (DSM 112478T = NCTC 14603T).

Determination of Kinematic Viscosity of Mg(ClO4)2 and KOH Brines Saturated with CO2 at Sub-Zero Temperatures

The current race for space exploration has hastened the development of electrochemical technologies for the in-situ utilisation of planetary resources for the synthesis of vital chemicals such as O2 and fuels. Understanding the physicochemical properties, such as the density and kinematic viscosity, of aqueous solutions is essential for the design of electrochemical devices for the electrolysis of water and CO2, particularly at low temperatures. The density and kinematic viscosity of highly concentrated Mg(ClO4)2 and KOH solutions have been determined, both at low temperatures and in the presence of CO2 gas. It was found that, for all of the solutions, independent of the concentration or nature of the electrolyte, as the temperature was decreased to 255 K, the density and the viscosity of the solutions increased. Upon saturation with CO2, no significant change to the density and viscosity of Mg(ClO4)2, at all of the temperatures measured, was observed. Conversely, the CO2 saturated solutions of KOH showed significant changes in density and viscosity at all temperatures, likely due to the formation of carbonates. The effects of these changes on the diffusion coefficient for dissolved CO2 is also discussed.

Pyrochlores for Advanced Oxygen Electrocatalysis

Fuel cells (FCs), water electrolyzers (WEs), unitized regenerative fuel cells (URFCs), and metal-air batteries (MABs) are among the emerging electrochemical technologies for energy storage, fuel (H₂), oxidant (O₂), and clean energy production. Their commercial applications are hindered by the low oxygen reduction reaction/oxygen evolution reaction (ORR/OER) bifunctional activity (for URFCs and MABs), OER selectivity (brine electrolysis in seawater and Martian environments), and high cost of the benchmark electrocatalysts (OER: RuO₂, IrO₂ and ORR: Pt/C) which affects the performance and affordability of the devices. Low-cost electrocatalysts with highly symmetric ORR/OER bifunctional activity and high OER selectivity are crucial for large-scale FC, WE, URFC, and MAB application. Recent studies have revealed that tuning the structure of pyrochlore oxides provides a pathway to enhancing OER and ORR activity over a wide range of pH. Pyrochlore oxides commonly contain a cubic A₂B₂O_7-x structure with two types of tetrahedrally coordinated O atoms containing (1) A-O-A and (2) A-O-B types with a cationic radii mismatch of r_A/r_B > 1.5 and propensity toward oxygen vacancy formation. The variety of pyrochlore oxides and their tunable properties make them attractive for a wide spectrum of applications. Among all the metal oxides, Ru-based pyrochlores (e.g., Pb₂Ru₂O_7-x) exhibit the best bifunctional oxygen electrocatalytic activity, i.e., low bifunctionality index (BI), in alkaline medium. Furthermore, pyrochlores exhibit high OER selectivity in brine electrolytes due to the presence of surface oxygen vacancies, making them suitable for space applications (brine electrolysis on Mars) and coastal hydrogen generation. Their bifunctional activity and selectivity can be further amplified by (1) substituting "A" and "B" sites of pyrochlores (AA'BB'O_7-x), (2) tuning metal oxidation states of A and B by varying synthesis conditions, and (3) modulating oxygen vacancy concentration, each of which yield favorable structural and electronic variations. In recent years, research on the synthesis and understanding of pyrochlores has significantly enhanced their viability, offering a new horizon in the quest for economical and active electrocatalysts. However, an account that focuses on critical developments in this field is still lacking.In this Account, we focus on the recent development of a variety of pyrochlore electrocatalysts to understand intrinsic structure-activity-selectivity-stability relationships in these materials. Recent developments and applications of pyrochlore-based electrocatalysts are discussed under the following headings: (1) modulation of crystal and electronic structure of pyrochlores, (2) structure-activity-stability relationships of different pyrochlores for OER and ORR, (3) development of OER-selective pyrochlores for brine electrolysis, and (4) the application of pyrochlores in electrochemical devices. Finally, we highlight some unaddressed issues such as the precise identification of active sites, which can be addressed in the future through advanced in situ and ex situ characterization techniques coupled with the density functional theory-based analyses. This Account provides foundational understanding to guide the comprehensive development of highly active, selective, stable and low-cost structurally engineered pyrochlores for high performance electrochemical devices.

Cyanobacteria as Candidates to Support Mars Colonization: Growth and Biofertilization Potential Using Mars Regolith as a Resource

Cyanobacteria are indicated as organisms that can possibly support Mars colonization, contributing to the production of oxygen and other commodities therein. In this general context, the aim of this work was to evaluate the ability of three species of cyanobacteria (Anabaena cylindrica, Nostoc muscorum, and Arthrospira platensis) and a green microalga (Chlorella vulgaris) to grow using only the resources existing in Mars, i.e., water and Martian regolith stimulant (MGS-1), under an Earth-like atmosphere. A Martian regolith extract was produced and used as a culture medium to grow these species. Their growth was assessed during a period of 25 days, using optical density and fluorometric parameters. After this period, the possible contribution of end-of-life cyanobacteria/microalga as biofertilizing agents was also assessed, using the macrophyte Lemna minor as a vegetable model. Among the three species, N. muscorum showed the best growth performance when compared to the other species, while A. platensis and C. vulgaris were not able to thrive on Mars regolith extract. Therefore, N. muscorum should be the target of future studies not only due to their role in oxygen production but also due to their possible use as a food source, as many members of the Nostoc genus. Cyanobacteria and microalgae (A. platensis and C. vulgaris) showed good abilities as biofertilizing agents, i.e., they stimulated biomass (i.e., dry weight) production at levels comparable to the plants that grew on standard synthetic medium. The highest yield was reached with A. platensis, while the lowest was achieved using the media with N. muscorum. FTIR-ATR (Fourier transform infrared with attenuated total reflectance) spectroscopy showed that the differences between the plants grown on media with or without Martian regolith seem to be related mainly to polysaccharides.

High-performance AEM unitized regenerative fuel cell using Pt-pyrochlore as bifunctional oxygen electrocatalyst

The performance of fixed-gas unitized regenerative fuel cells (FG-URFCs) are limited by the bifunctional activity of the oxygen electrocatalyst. It is essential to have a good bifunctional oxygen electrocatalyst which can exhibit high activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In this regard, Pt-Pb₂Ru₂O_7-x is synthesized by depositing Pt on Pb₂Ru₂O_7-x wherein Pt individually exhibits high ORR while Pb₂Ru₂O_7-x shows high OER and moderate ORR activity. Pt-Pb₂Ru₂O_7-x exhibits higher OER (η_@10mAcm-2 = 0.25 ± 0.01 V) and ORR (η_@-3mAcm-2 = -0.31 ± 0.02 V) activity in comparison to benchmark OER (IrO₂, η_@10mAcm-2 = 0.35 ± 0.02 V) and ORR (Pt/C, η_@-3mAcm-2 = -0.33 ± 0.02 V) electrocatalysts, respectively. Pt-Pb₂Ru₂O_7-x shows a lower bifunctionality index (η_{@10mAcm-2, OER} ^- η_{@-3mAcm-2, ORR}) of 0.56 V with more symmetric OER-ORR activity profile than both Pt (>1.0 V) and Pb₂Ru₂O_7-x (0.69 V) making it more useful for the AEM (anion exchange membrane) URFC or metal-air battery applications. FG-URFC tested with Pt-Pb₂Ru₂O_7-x and Pt/C as bifunctional oxygen electrocatalyst and bifunctional hydrogen electrocatalyst, respectively, yields a mass-specific current density of 715 ± 11 A/g_cat ^-1 at 1.8 V and 56 ± 2 A/g_cat ^-1 at 0.9 V under electrolyzer mode and fuel-cell mode, respectively. The FG-URFC shows a round-trip efficiency of 75% at 0.1 A/cm^-2, underlying improvement in AEM FG-URFC electrocatalyst design.

A Bioinspired Molybdenum Catalyst for Aqueous Perchlorate Reduction

Perchlorate (ClO₄^-) is a pervasive, harmful, and inert anion on both Earth and Mars. Current technologies for ClO₄^- reduction entail either harsh conditions or multicomponent enzymatic processes. Herein, we report a heterogeneous (L)Mo-Pd/C catalyst directly prepared from Na₂MoO₄, a bidentate nitrogen ligand (L), and Pd/C to reduce aqueous ClO₄^- into Cl^- with 1 atm of H₂ at room temperature. A suite of instrument characterizations and probing reactions suggest that the Mo^VI precursor and L at the optimal 1:1 ratio are transformed in situ into oligomeric Mo^IV active sites at the carbon-water interface. For each Mo site, the initial turnover frequency (TOF₀) for oxygen atom transfer from ClO_x^- substrates reached 165 h^-1. The turnover number (TON) reached 3840 after a single batch reduction of 100 mM ClO₄^-. This study provides a water-compatible, efficient, and robust catalyst to degrade and utilize ClO₄^- for water purification and space exploration.