Coordination Engineering of N,O Co-Doped Cu Single Atom on Porous Carbon for High Performance Zinc Metal Anodes

Traditional challenges of poor cycling stability and low Coulombic efficiency in Zinc (Zn) metal anodes have limited their practical application. To overcome these issues, this work introduces a single metal-atom design featuring atomically dispersed single copper (Cu) atoms on 3D nitrogen (N) and oxygen (O) co-doped porous carbon (CuNOC) as a highly reversible Zn host. The CuNOC structure provides highly active sites for initial Zn nucleation and further promotes uniform Zn deposition. The 3D porous architecture further mitigates the volume changes during the cycle with homogeneous Zn²⁺ flux. Consequently, CuNOC demonstrates exceptional reversibility in Zn plating/stripping processes over 1000 cycles at 2 and 5 mA cm⁻² with a fixed capacity of 1 mAh cm⁻², while achieving stable operation and low voltage hysteresis over 700 h at 5 mA cm⁻² and 5 mAh cm⁻². Furthermore, density functional theory calculations show that co-doping N and O on porous carbon with atomically dispersed single Cu atoms creates an efficient zincophilic site for stable Zn nucleation. A full cell with the CuNOC host anode and high loading V₂O₅ cathode exhibits outstanding rate-capability up to 5 A g⁻¹ and a stable cycle life over 400 cycles at 0.5 A g⁻¹.     

Microbial population and functional dynamics associated with surface potential and carbon metabolism

Microbial extracellular electron transfer (EET) to solid surfaces is an important reaction for metal reduction occurring in various anoxic environments. However, it is challenging to accurately characterize EET-active microbial communities and each member''s contribution to EET reactions because of changes in composition and concentrations of electron donors and solid-phase acceptors. Here, we used bioelectrochemical systems to systematically evaluate the synergistic effects of carbon source and surface redox potential on EET-active microbial community development, metabolic networks and overall electron transfer rates. The results indicate that faster biocatalytic rates were observed under electropositive electrode surface potential conditions, and under fatty acid-fed conditions. Temporal 16S rRNA-based microbial community analyses showed that Geobacter phylotypes were highly diverse and apparently dependent on surface potentials. The well-known electrogenic microbes affiliated with the Geobacter metallireducens clade were associated with lower surface potentials and less current generation, whereas Geobacter subsurface clades 1 and 2 were associated with higher surface potentials and greater current generation. An association was also observed between specific fermentative phylotypes and Geobacter phylotypes at specific surface potentials. When sugars were present, Tolumonas and Aeromonas phylotypes were preferentially associated with lower surface potentials, whereas Lactococcus phylotypes were found to be closely associated with Geobacter subsurface clades 1 and 2 phylotypes under higher surface potential conditions. Collectively, these results suggest that surface potentials provide a strong selective pressure, at the species and strain level, for both solid surface respirators and fermentative microbes throughout the EET-active community development.     

Hydrogen consumption in microbial electrochemical systems (MXCs): The role of homo-acetogenic bacteria

Homo-acetogens in the anode of a microbial electrolysis cell (MEC) fed with H₂ as sole electron donor allowed current densities similar to acetate-fed biofilm anodes (∼10 A/m²). Evidence for homo-acetogens included accumulation of acetate at high concentrations (up to 18 mM) in the anode compartment; detection of formate, a known intermediate during reductive acetogenesis by the acetyl-CoA pathway; and detection of formyl tetrahydrofolate synthetase (FTHFS) genes by quantitative real-time PCR. Current production and acetate accumulation increased in parallel in batch and continuous mode, while both values decreased simultaneously at short hydraulic retention times (1 h) in the anode compartment, which limited suspended homo-acetogens. Acetate produced by homo-acetogens accounted for about 88% of the current density of 10 A/m², but the current density was sustained at 4 A/m² at short hydraulic retention time because of a robust partnership of homo-acetogens and anode respiring bacteria (ARB) in the biofilm anode.     

The Relationship of Cobalt Requirement to Vitamin B12-dependent Methionine Synthesis in Rhizobium meliloti

As a growth factor, Rhizobium meliloti required cobalt ion, or vitamin B₁₂ which was found to be incorporated into the cells without decomposition to cobalt ion. Trial of replacement for cobalt ion by the addition of various compounds to the cobalt-deficient medium revealed that methionine could substitute for cobalt ion and promote the growth in response to its concentration. Furthermore, B₁₂-dependent methionine synthetase was demonstrated in the cell-free extracts of this microorganism. The morphological change of R. meliloti by the additions to the medium was observed microscopically.     

Stratified microbial structure and activity within anode biofilm during electrochemically assisted brewery wastewater treatment

In a bioelectrochemical system (BES), microbial community of anode biofilm is crucial to BES performance. In this study, the stratified pattern of community structure and activity of an anode-respiring biofilm in a BES fueled with brewery wastewater was investigated over time. The anode biofilm exhibited a superior performance in the removal of ethanol to that of an open-circuit system. The electrical current density reached a high level of 0.55mA/cm² with a Coulombic efficiency of 71.4%, but decreased to 0.18mA/cm² in the late stage of operation. A mature biofilm developed a more active outer layer covering a less active inner core, although the activities of the outer and inner layers of biofilm were similar in the early stage. More Geobacter spp., typical exoelectrogens, were enriched in the outer layer than in the inner layer of biofilm in the early stage, while more Geobacter spp. were distributed in the inner layer than in the outer layer in the late stage. The inactive and Geobacter-occupied inner layer of biofilm might be responsible for the decreased electricity generation from wastewater in the late stage of operation. This study provides better understanding of the effect of anode biofilm structure on BES performance.     

Realizing Reversible Conversion‐Alloying of Sb(V) in Polyantimonic Acid for Fast and Durable Lithium‐ and Potassium‐Ion Storage

Finding suitable electrode materials for alkali‐metal‐ion storage is vital to the next‐generation energy‐storage technologies. Polyantimonic acid (PAA, H₂Sb₂O₆ · nH₂O), having pentavalent antimony species and an interconnected tunnel‐like pyrochlore crystal framework, is a promising high‐capacity energy‐storage material. Fabricating electrochemically reversible PAA electrode materials for alkali‐metal‐ion storage is a challenge and has never been reported due to the extremely poor intrinsic electronic conductivity of PAA associated with the highest oxidation state Sb(V). Combining nanostructure engineering with a conductive‐network construction strategy, here is reported a facile one‐pot synthesis protocol for crafting uniform internal‐void‐containing PAA nano‐octahedra in a composite with nitrogen‐doped reduced graphene oxide nanosheets (PAA?N‐RGO), and for the first time, realizing the reversible storage of both Li⁺ and K⁺ ions in PAA?N‐RGO. Such an architecture, as validated by theoretical calculations and ex/in situ experiments, not only fully takes advantage of the large‐sized tunnel transport pathways (0.37 nm²) of PAA for fast solid‐phase ionic diffusion but also leads to exponentially increased electrical conductivity (3.3 S cm^?1 in PAA?N‐RGO vs 4.8 × 10^?10 S cm^?1 in bare‐PAA) and yields an inside‐out buffer function for accommodating volume expansion. Compared to electrochemically irreversible bare‐PAA, PAA?N‐RGO manifests reversible conversion‐alloying of Sb(V) toward fast and durable Li⁺‐ and K⁺‐ion storage.     

Chemical Studies on Components of Dried Bonito, “Katsuobushi”

Volatile components obtained by the extraction of “Katsuobushi” with 80% ethanol and by the subsequent steam distillation of the extract were fractionated by the usual methods, and the resulting hydrocarbon fraction was investigated. Gas chromatographic study on this fraction originated from “Katsuobushi” of bonito (Katsuwonus pelamis) revealed 9 hydrocarbons, including n-tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane, n-eicosane, n-heneicosane and n-docosane, which were tentatively identified by the retention times with the aid of authentic hydrocarbons. n-Pentadecane and n-heptadecane that were main components among these hydrocarbons were identified further by NMR and IR spectrometry. “Katsuobushi” of frigate mackerel (Auxis thazard), mackerel (Scomber Japonicus Houttuyn) or muroaji (Decapterus muroadsi) also contained n-penta-decane and n-heptadecane in large amounts, but did other hydrocarbons in negligible amounts.

Possible mechanisms of the hydrocarbon formation during the processing of “Katsuobushi” were discussed.     

Analysis of a microbial electrochemical cell using the proton condition in biofilm (PCBIOFILM) model

Common to all microbial electrochemical cells (MXCs) are the anode-respiring bacteria (ARB), which transfer electrons to an anode and release protons that must transport out of the biofilm. Here, we develop a novel modeling platform, Proton Condition in BIOFILM (PCBIOFILM), with a structure geared towards mechanistically explaining: (1) how the ARB half reaction produces enough acid to inhibit the ARB by low pH; (2) how the diffusion of alkalinity carriers (phosphates and carbonates) control the pH gradients in the biofilm anode; (3) how increasing alkalinity attenuates pH gradients and increases current; and (4) why carbonates enable higher current density than phosphates. Analysis of literature data using PCBIOFILM supports the hypothesis that alkalinity limits the maximum current density for MXCs. An alkalinity criterion for eliminating low-pH limitation - 12 mg CaCO₃/mg BOD - implies that a practical MXC can achieve a maximum current density with an effluent quality comparable to anaerobic digestion.