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Described herein are stable hybrid peroxidases capable of oxidizing manganese and high-reduction potential substrates, methods of generating such peroxidases, and method of using the peroxidases in reactions that are less environmentally toxic.
A secondary alkaline battery includes an anode, a cathode, and an electrolyte. The cathode includes a current collector, a cathode mixture in electrical contact with the current collector. The cathode mixture comprises: manganese oxide, a copper compound comprising copper, a salt of copper, an alloy thereof, or any combination thereof, a bismuth compound comprising bismuth, a salt of bismuth, or any combination thereof, and a conductive carbon. The secondary alkaline battery can also include a first composition in contact with the current collector and disposed between the current collector and the cathode mixture that includes copper, a salt of copper, an alloy thereof, or a combination thereof.
We report manganese (Mn) oxides have a high surface area and redox potential that facilitate sorption and/or oxidation of organic carbon (OC), but their role in regulating soil C storage is relatively unexplored. Small OC compounds with distinct structures were reacted with Mn(III/IV)-oxides to investigate the effects of OC/Mn molar ratios on Mn–OC interaction mechanisms. Dissolved and solid-phase OC and Mn were measured to quantify the OC sorption to and/or the redox reaction with Mn-oxides. Mineral transformation was evaluated using X-ray diffraction and X-ray absorption spectroscopy. Higher OC/Mn ratios resulted in higher sorption and/or redox transformation; however, interaction mechanisms differed at low or high OC/Mn ratios for some OC. Citrate, pyruvate, ascorbate, and catechol induced Mn-oxide dissolution. The average oxidation state of Mn in the solid phase did not change during the reaction with citrate, suggesting ligand-promoted mineral dissolution, but decreased significantly during reactions with the other compounds, suggesting reductive dissolution mechanisms. Phthalate primarily sorbed on Mn-oxides with no detectable formation of redox products. Mn–OC interactions led primarily to C loss through OC oxidation into inorganic C, except phthalate, which was predominantly immobilized in the solid phase. Together, these results provided detailed fundamental insights into reactions happening at organo–mineral interfaces in soils.
Energy storage plays an essential role for sustainable and renewable energy use in an effort to reduce carbon emissions. Thermochemical energy storage (TCES) is a favorable alternative to fossil fuel energy systems and a promising solution to the intermittency problem of renewable energy sources (such as solar energy). TCES stores energy in the form of chemical bonds using reversible redox reactions (such as manganese metal oxides). This study developed manganese oxide (Mn2O3) and iron oxide (Fe2O3) with an inert dispersant of silicon dioxide (SiO2) (Mn-Fe-Si) for potential large scale energy storage application. These metal oxides are nontoxic, cheap, and relatively abundant. The materials were prepared with varying metal oxide content using physical mixing in a ball mill, pressure pelletization and calcination at different temperatures. Redox cycle tests were conducted using differential scanning calorimetry combined with thermogravimetric analysis (TGA-DSC). The Mn-Fe-Si materials had higher cyclability and energy release compared to the pure metal oxides and manganese oxide with SiO2. The calcination temperature had a significant effect on releasable energy due to the interactions between the oxides. The Mn-Fe-Si mixture calcined at high temperature (1000oC) showed the highest average energy storage density.
The reduction of carbon dioxide (CO 2 ) to formate using molecular catalysts immobilized on high surface area porous silicon is described. Manganese complexes of the type ( R bpy)Mn(CO) 3 Br (bpy = 2,2′-bipyridine) were prepared with silatrane groups on the bpy ligand for attachment to oxide-coated porous silicon (SiO x -porSi). SiO x -porSi wafers were formed by heating hydrogen-terminated p-type porous silicon wafers under air, and the manganese complexes were immobilized on SiO x -porSi by heating at 80°C. The resulting hybrid photoelectrodes are photoelectrocatalysts for CO 2 reduction in acetonitrile containing 2.0 M triethylamine and 2.0 M isopropanol, yielding formate with high selectivity (>96%) and current density (∼0.6 mA/cm 2 ), excellent reproducibility, and a photovoltage of 280 mV at −1.75 V (versus ferrocenium/ferrocene) under 1 sun illumination. Here, the applied potential is close to the equilibrium potential for CO 2 reduction to formate. This work presents rare examples of immobilized molecular catalysts for CO 2 reduction to formate and the first on semiconducting silicon.
Lithium- and manganese-rich oxides are of interest as lithium-ion battery cathode materials as Mn is earth abundant, low cost, and can deliver high capacity. Herein, a high entropy strategy was used to prepare Mn rich high entropy oxide (HEO) materials by including four additional metals (Ni, Co, Fe and Al) in the compositions using a mild co-precipitation method. Two HEOs (Li x Ni 0.1 Mn 0.6 Co 0.1 Al 0.1 Fe 0.1 O y , where x = 1.5 for HEO-L and x = 0.5 for HEO-H) with layered and spinel-layered hybrid structures were investigated where the morphology, elemental composition, structure, atomic level phase distribution, and electrochemistry were determined. The HEO-L samples involve a Li 2 TMO 3 layered structure with ~39% stacking faults. HEO-H is a hybrid structure comprised of 80 wt% spinel and 20 wt% LiMO 2 layered structure. The high entropy manganese-rich HEO-L showed higher capacity and 93% retention of the average voltage after 100 cycles while HEO-H showed higher capacity retention and near 100% average voltage retention. Finally, operando X-ray absorption spectroscopy revealed that the Ni, Co, and Mn are redox active in both materials while the Fe center remains at the Fe 3+ oxidation state throughout cycling, where the changes in the oxidation states for both materials during discharge were consistent with the delivered electrochemical capacity rationalizing the observed electrochemistry.
We report improving sluggish rate performance and cycling stability of Li, Mn-rich cathode materials (LMR) is of great importance for practical implementation. Here, dual surface modification on LMR particles with formic acid washing and spinel coating improves the electrochemical performance. Dilute formic acid can remove the Li2CO3 surface impurities and selectively reduce Ni while significantly increasing specific surface area by ~32 %, unlocking more electrochemically active surfaces. Spinel coating enhances cycle stability by suppressing detrimental side reactions at electrode-electrolyte interfaces at high voltage. Post-annealing temperature was found to significantly affect the cathode performance. Higher temperature favors diffusion of transition metal (TM)/Li ions of the spinel coating from surface to the bulk, removing the coating by possible reconstruction into the layered structure and thus degrading the performance. The spinel coating also appears to increase Co 3+ segregation on the particle surface. Compared to the original material, the optimized sample demonstrates 47 % higher capacity retention at 3C and retains 89 % of initial capacity after 150 cycles at 0.5C. Besides, the specific energy density of 523 Wh kg -1 can be attained after 150 cycles at 0.5C. Moreover, the post-cycling analysis of modified sample verifies a better structural integrity with less particle cracking. Altogether, this study portrays an alternative strategy to overcome the shortcomings of LMR cathode materials.
We report that direct Li-ion battery recycling involves separating cathode active materials in the solid phase while preserving their electrochemical performance. To reuse the recycled ones in new batteries, it is necessary to separate individual cathode components, which would typically occur prior to the rejuvenation and any compositional reformulation processes. Herein, a froth flotation process is developed to separate pristine lithium nickel-manganese-cobalt oxide (LiNi 0.333 Mn 0.333 Co 0.333 O 2 , NMC111) and lithium manganese oxide (LMO) materials. The flotation results show that with multiple stages of the separation processes, a satisfactory separation is achieved with 95% grade or above of NMC111 in the froth product and 95% grade of LMO in the tailing product. The electrochemistry results show that the flotation chemicals have negligible impact on the electrochemical performance of recycled active materials, whereas the NMC111 exhibits a minor capacity fade after being in contact with deionized water at 2% solid concentration. An improvement in both the rate and cycling performance is achieved at 10% solid concentration or higher. It is found that there is little compositional and structural change to the aqueous recycled NMC111 powders. An effective and low-cost separation method for direct recycling mixed cathode compositions is demonstrated.
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Biogenic manganese (Mn) oxides occur ubiquitously in the environment including the uranium (U) mill tailings at the Ningyo-toge U mine in Okayama, Japan, being important in the sequestration of radioactive radium (Ra). To understand the nanoscale processes in Mn oxides formation at the U mill tailings site, Mn 2+ absorption by a basidiomycete fungus, Coprinopsis urticicola, isolated from Ningyo-toge mine water samples, was investigated in the laboratory under controlled conditions utilizing electron microscopy, synchrotron-based X-ray analysis, and fluorescence microscopy with molecular pH probe. The fungus’ growth was first investigated in an agar-solidified medium supplemented with 1.0 mmol/L of Mn 2+ , ± Cu 2+ (50 – 200 µM), ± Zn 2+ (50 – 200 µM), or ± diphenyleneiodonium chloride (DPI) (50 – 100 µM) at 25 °C. The results revealed that Zn 2+ has no significant effects on the Mn oxides formation, whereas Cu 2+ and DPI significantly inhibit both fungal growth and Mn oxidation, indicating superoxide-mediated Mn oxidation. During the interaction of Mn 2+ with the fungi in solution medium at the initial pH of 5.67, a small fraction of Mn 2+ infiltrated into the fungal hyphae within 8 h, forming a few tens nm-sized concentrates of soluble Mn2+ in the intracellular pH of ~6.5, which can be released back to solution within a day as shown in a subsequent releasing experiment. After 1 day of incubation, Mn oxides began to precipitate on the hyphae, which were characterized to be fibrous nanocrystals with a hexagonal birnessite-structure, these forming spherical aggregates with a diameter of ~1.5 µm. When the fungi were reacted using the Ningyo-toge mine water, the Mn concentration decreased at a rate of 1.0 mmol·day-1 per unit dry weight. The nanoscale processes associated with the fungi derived from the Ningyo-toge mine area provides additional insights into the existing mechanisms of Mn oxidation by filamentous fungi at other U mill tailings sites under circumneutral pH conditions. Such processes add to the class of reactions important to the sequestration of toxic elements.
Biogenic isoprene is an important pollutant for regional air quality. Being ubiquitously distributed on the earth surface, manganese (hydr)oxides should play a vital role in the transformation of isoprene. Cryptomelane is a typical manganese oxide with isomorphous substitution of Fe for Mn, but less attention has been paid to its heterogeneous reaction with isoprene. When Fe 3+ replaces Mn 3+ , K + is depleted and Mn 3+ is oxidized to Mn 4+ . In contrast, oxygen vacancies are formed when Fe 3+ substitutes Mn 4+ . Fe substitution creates weak crystallites and abundant mesopores, resulting in the increase of isoprene adsorption. As found by theoretical calculations, the Mn 4+ –O 2- bonds at the cross sections of the tunnels is more active than that on the outer wall of the tunnels. After the adsorption of isoprene, bridging carboxylate species and hydrogen-bonding water are produced and the surface octahedra are distorted, i.e., Mn 4+ O 6 → Mn 3+ O 6-δ . As the heat facilitates the breakage of Mn 4+ –O 2- , the increase of environmental temperature enhances the oxidation of isoprene. Here the above findings shed light on the effect of Fe substitution in cryptomelane to enhance the oxidation of isoprene, and illustrates that heterogeneous reaction with isoprene impairs the transformation of other environmental substances on cryptomelane.
In this work, a continuum heat and mass transfer model coupling transport phenomena and high-temperature thermochemical reactions is developed for stationary packed-bed and counter-flow moving-bed reactors. After presenting the general modeling framework, we focus on the 2D axisymmetric version of the model for which validation is conducted with experimental results for a packed-bed reactor in the literature for manganese-iron oxide reduction/oxidation and an in-house counter-flow moving-bed reactor for magnesium-manganese oxide reduction up to 1450 °C. Transient simulation results including the local distributions of gas/solid temperatures, oxygen concentration and the extent of reaction, as well as the various energy flow components and energy conversion efficiencies are reported. The results based on the 2D axisymmetric model are also compared with those obtained from a previous 1D model. The comparison shows that capturing the radial variation is critical in reactor modeling and the 2D results demonstrate improved agreement with experiments. Specifically, large temperature variations along the radial direction are observed especially in the reaction zone; this non-uniform radial temperature distribution has a significant effect on the chemical reaction extent due to its strong dependence on temperature; and the overall oxygen concentration at the reactor exit and the predicted system efficiency are slightly lower in the 2D model compared to the 1D model. Finally, the present heat and mass transfer model can provide valuable insights into reactor design, scale-up, and operating conditions selection to maximize system energy storage efficiency.
Disordered rock-salt oxides and oxyfluorides are promising positive electrode materials for high-performance lithium-ion batteries free of nickel and cobalt. However, conventional synthesis methods rely on post-synthesis pulverization to achieve cycling-appropriate particle sizes, offering limited control over particle microstructure and crystallinity. This accelerates degradation and complicates secondary particle processing. Here we present a synthesis strategy that enhances nucleation while suppressing particle growth and agglomeration across various disordered rock-salt compositions, including lithium–manganese–titanium oxide, lithium–manganese–niobium oxide, and lithium–nickel–titanium oxide systems. Applied to Li 1.2 Mn 0.4 Ti 0.4 O 2 , this method yields highly crystalline, well-dispersed sub-200 nm particles that form homogeneous electrode films with stable cycling behavior. Tested in cells with lithium metal as the counter electrode, these electrodes deliver ~200 mAh/g with 85% capacity retention relative to the first cycle after 100 cycles (20 mA/g, 1.5–4.8 V), and an average discharge voltage loss of 4.8 mV per cycle, compared to 38.6% retention and 7.5 mV loss per cycle for electrodes derived from pulverized solid-state particles. This approach suggests a route to enhance the performance and durability of disordered rock-salt electrodes for sustainable lithium-ion batteries.
The occurrence of manganese (Mn) oxides on Mars is believed to be an indicator of an O 2 -rich paleoenvironment of Mars because Mn oxides often form through the oxidation of Mn(II) by O 2 on the surface of Earth. An alternative formation pathway was recently proposed, in which Mn(II) is oxidized by bromate (BrO 3 - ), a common oxidant in contemporary Martian regolith. However, the oxidation of Mn(II) by bromate in solution is kinetically controlled and slow unless using very high concentrations (100 mM) of reactants that may be irrelevant to the conditions of Mars. We conducted laboratory simulations to determine whether iron (Fe) oxides (hematite and goethite) and a phyllosilicate (montmorillonite), abundant minerals on the surface of Mars, could catalyze the oxidation of Mn(II) by bromate. Hematite and goethite, but not montmorillonite, dramatically accelerated the oxidation with a low concentration (1 mM) of Mn(II) and bromate under various solution conditions. Further, the reaction system was autocatalytic with Fe oxides initiating the oxidation of Mn(II) at the early stage and the subsequent catalysis mainly provided by the Mn oxide products. In contrast to producing Mn(IV)O 2 only during the homogeneous oxidation of Mn(II) by bromate in solutions, the heterogeneous mineral-surface catalyzed oxidation resulted in a mixture of Mn(III)OOH and Mn(IV)O 2 phases. Mn(III)OOH was an intermediate product and can be further oxidized by bromate to Mn(IV)O 2 . The occurrence and accumulation of the intermediate product MnOOH can be attributed to its rapid formation due to surface-enhanced nucleation and growth on Fe oxide surfaces and to its higher resistance to oxidation by bromate than Mn(III) ions or clusters. Overall, mineralsurface catalyzed oxidation of Mn(II) by bromate is favorable from both thermodynamic and kinetic perspectives, and can be a major pathway for the occurrence of Mn oxides on Mars where microorganisms are lacking to catalyze the reaction. Our study further improves our understanding of the thermodynamic and kinetic controls on Mn(II) oxidation.
High-nickel LiNi 1–x–y Mn x Co y O 2 and LiNi 1–x–y Co x Al y O 2 cathodes are receiving growing attention due to the burgeoning demands on high-energy-density lithium-ion batteries. The presence of both cobalt and manganese in them, however, triggers multiple issues, including high cost, high toxicity, rapid surface deterioration, and severe transition-metal dissolution. Herein, a Co- and Mn-free ultrahigh-nickel LiNi 0.93 Al 0.05 Ti 0.01 Mg 0.01 O 2 (NATM) cathode that exhibits 82% capacity retention over 800 deep cycles in full cells, outperforming two representative high-Ni cathodes LiNi 0.94 Co 0.06 O 2 (NC, 52%) and LiNi 0.90 Mn 0.05 Co 0.05 O 2 (NMC, 60%) is presented. It is demonstrated that a titanium-enriched surface along with aluminum and magnesium as the stabilizing ions in NATM not only ameliorates unwanted side reactions with the electrolyte and structural disintegrity, but also mitigates transition-metal dissolution and active lithium loss on the graphite anode. As a result, the graphite anode paired with NATM displays an ultrathin (≈8 nm), monolayer anode-electrolyte interphase architecture after extensive cycling. Furthermore, NATM displays considerably enhanced thermal stability with an elevated exothermic temperature (213 °C for NATM vs 180 and 190 °C for NC and NMC, respectively) and remarkably reduced heat release. This work sheds light on rational compositional design to adopt ultrahigh-Ni cathodes in lithium-based batteries with low cost, long service life, and improved thermal stability.
Natural manganese (Mn) oxide coatings, resulting from the heterogeneous nucleation on foreign substances, have garnered interest based on their importance in the reaction with organic substances and in environmental systems. However, the heterogeneous nucleation of the natural Mn oxide coatings still remains elusive. Here, via fast photochemical oxidation of Mn 2+ (aq), we show that Mn(IV) oxide nuclei form and aggregate on quartz in three distinct successive stages: (i) a nanocrystalline film of unaligned grain forms, (ii) nanoislands develop on the film, and (iii) nanorods form on the nanoislands. Each stage has different crystalline structures and forms by aligned attachment of nanoscale precursors on the preceding surface. Crystal lattice analyses confirm the crystalline development, from the short-range order of the Mn oxide film to the long-range order of the nanorods. Also, the heterogeneous nucleation observed in this work produced groutellite-like tunnel structures of Mn oxide on quartz. Furthermore, this revealed pathway of the heterogeneous nucleation can offer a new perspective on the variety of poorly crystalline structures of natural Mn oxides found in the environment, which can affect elemental redox cycles, contaminant sequestration and removal, and soil carbon storage.
Manganese (Mn)-oxides regulate carbon (C) cycling in soils by sorbing and oxidizing organic compounds. The composition of soil organic matter varies widely, and little is known about the reactivity of individual organic compounds with structurally diverse Mn-oxides under various environmentally relevant pH conditions. Here, in this study, we examined the affinity of six organic compounds for three Mn-oxides, comprised of layer (birnessite and hydrous Mn oxide HMO) or tunnel (cryptomelane) structures, at acidic (pH 4), slightly acidic (pH 6), and slightly alkaline (pH 8) conditions. Cryptomelane, with a higher specific surface area and point of zero charge, showed higher reactivity than that of HMO and birnessite. Interestingly, these Mn-oxides, although different in structures, decomposed each organic compound to form the same products. Citrate, pyruvate, ascorbate, and catechol induced reduction and dissolution of Mn-oxides. After the reaction, the average oxidation state of Mn in the solids was much lower at pH 4 than at pH 6 and 8, suggesting more reduction under more acidic conditions. Even when reacting with phthalate and propanol, which only sorbed to Mn-oxides but did not degrade, there was proton-promoted Mn dissolution under acidic conditions. These results suggest the significance of environmental pH and mineral structures in affecting the Mn–organic interactions and provide fundamental insights into a better understanding of the roles of Mn-oxides in regulating soil C cycling.
Manganese has been observed on Mars by the NASA Curiosity rover in a variety of contexts and is an important indicator of redox processes in hydrologic systems on Earth. Within the Murray formation, an ancient primarily fine-grained lacustrine sedimentary deposit in Gale crater, Mars, have observed up to 45× enrichment in manganese and up to 1.5× enrichment in iron within coarser grained bedrock targets compared to the mean Murray sediment composition. This enrichment in manganese coincides with the transition between two stratigraphic units within the Murray: Sutton Island, interpreted as a lake margin environment, and Blunts Point, interpreted as a lake environment. On Earth, lacustrine environments are common locations of manganese precipitation due to highly oxidizing conditions in the lakes. Here, we explore three mechanisms for ferromanganese oxide precipitation at this location: authigenic precipitation from lake water along a lake shore, authigenic precipitation from reduced groundwater discharging through porous sands along a lake shore, and early diagenetic precipitation from groundwater through porous sands. All three scenarios require highly oxidizing conditions and we discuss oxidants that may be responsible for the oxidation and precipitation of manganese oxides. This work has important implications for the habitability of Mars to microbes that could have used Mn redox reactions, owing to its multiple redox states, as an energy source for metabolism.