Efficient multicarbon formation in acidic CO2 reduction via tandem electrocatalysis.

The electrochemical reduction of CO2 in acidic conditions enables high single-pass carbon efficiency. However, the competing hydrogen evolution reaction reduces selectivity in the electrochemical reduction of CO2, a reaction in which the formation of CO, and its ensuing coupling, are each essential to achieving multicarbon (C2+) product formation. These two reactions rely on distinct catalyst properties that are difficult to achieve in a single catalyst. Here we report decoupling the CO2-to-C2+ reaction into two steps, CO2-to-CO and CO-to-C2+, by deploying two distinct catalyst layers operating in tandem to achieve the desired transformation. The first catalyst, atomically dispersed cobalt phthalocyanine, reduces CO2 to CO with high selectivity. This process increases local CO availability to enhance the C-C coupling step implemented on the second catalyst layer, which is a Cu nanocatalyst with a Cu-ionomer interface. The optimized tandem electrodes achieve 61% C2H4 Faradaic efficiency and 82% C2+ Faradaic efficiency at 800 mA cm-2 at 25 °C. When optimized for single-pass utilization, the system reaches a single-pass carbon efficiency of 90 ± 3%, simultaneous with 55 ± 3% C2H4 Faradaic efficiency and a total C2+ Faradaic efficiency of 76 ± 2%, at 800 mA cm-2 with a CO2 flow rate of 2 ml min-1.

Atomic-Level Regulation of Cobalt Single-Atom Nanozymes: Engineering High-Efficiency Catalase Mimics.

Nanozymes aim to mimic the highly evolved active centers of natural enzymes. Despite progress in nanozyme engineering, their catalytic performance is much less favorable compared with natural enzymes. This study shows that precise control over the atomic configuration of the active centers of Co single-atom nanozymes (SAzymes) enables the rational regulation of their catalase-like performance guided by theorical calculations. The constructed Co-N3 PS SAzyme exhibits an excellent catalase-like activity and kinetics, exceeding the representative controls of Co-based SAzymes with different atomic configurations. Moreover, we developed an ordered structure-oriented coordination design strategy for rationally engineering SAzymes and established a correlation between the structure and enzyme-like performance. This work demonstrates that precise control over the active centers of SAzymes is an efficient strategy to mimic the highly evolved active sites of natural enzymes.

Synergistic effects of L-theanine and epigallocatechin gallate in alleviating ovalbumin allergy by regulating intestinal immunity through inhibition of mast cell degranulation.

Ovalbumin (OVA), a commonly consumed food protein, can cause severe allergies and intestinal immune disorders. L-Theanine (LTA) and epigallocatechin gallate (EGCG) regulate intestinal immunity. However, it is unclear whether an LTA and EGCG combined intervention can alleviate OVA allergy (OVA-A) by modulating intestinal-specific immunity, and it is unknown whether there is a synergistic effect between LTA and EGCG. Therefore, we treated BALB/c OVA-sensitized mice with LTA, EGCG, or a combination of both (LTA + EGCG) to investigate the effects of LTA and EGCG on intestinal-specific immunity regulation and underlying mechanisms. Female mice were intraperitoneally injected with OVA to establish OVA-sensitive mouse models. MLEO LTA + EGCG (20 mg kg-1 d-1 LTA + 80 mg kg-1 d-1 EGCG) and HLEO (30 mg kg-1 d-1 LTA + 120 mg kg-1 d-1 EGCG) exerted more beneficial effects on alleviating OVA-A (weight gain, allergy score, jejunum structure, mast cell [MC] degranulation, thymus and spleen indices) than LTA or EGCG alone (p < 0.01). Based on the alleviation of OVA-A by LTA + EGCG, we selected MLEO mice for 16S rDNA, flow cytometry, and western blot analyses. The 16S rDNA results showed that MLEO increased the abundance of Lactobacillaceae, Lachnospiraceae, and Ruminococcaceae, and decreased that of Helicobacteraceae (p < 0.01). The flow cytometry and western blotting results indicated that MLEO reduced the number of dendritic cells available to capture OVA, thereby lowering the Th2 immune response and decreasing the IL-4 and IL-13 levels. Meanwhile, the attenuation of the Th2 immune response inhibits the cross-linking of OVA and FcεRI, thus reducing MC degranulation and decreasing the serum HIS and mMCPT-1 levels through the FcεRI/Btk/PLCγ signaling pathway. LTA + EGCG also inhibits the Th2 immune response through the FcεRI/Lyn/Syk/PI3K/AKT signaling pathway and decreases the serum IL-4 and IL-13 levels. Notably, LTA + EGCG promotes the Treg and Th1 immune responses and inhibits the Th17 immune response, altering the levels of the corresponding cytokines. Therefore, LTA + EGCG can synergistically alleviate OVA-A by regulating intestinal immunity through MC degranulation inhibition.

L-Theanine Modulates Intestine-Specific Immunity by Regulating the Differentiation of CD4+ T Cells in Ovalbumin-Sensitized Mice.

Ovalbumin (OVA), a common food protein, can cause deadly allergies with intestine-specific immune reactions. L-Theanine (LTA) shows great potential for regulating intestinal immunity. To investigate the regulatory effect of LTA intervention on intestine-specific immunity, a 41 day experiment was performed on BALB/c OVA-sensitized mice. The results show that injecting female mice intraperitoneally with 50 µg of OVA and administering 30 mg of OVA 4 times can successfully establish an OVA-sensitized mouse model. LTA intervention significantly increased weight gain and thymus index (p < 0.05), decreased allergy and diarrhea scores (p < 0.05), and improved jejunum structure. Meanwhile, the histological score and degranulation of mast cells decreased. LTA intervention increased Clostridiales, Lachnospiraceae, Lactobacillus, Prevotella, and Ruminococcus abundance while decreasing Helicobacter abundance. Flow cytometry and Western blotting results indicated that 200 and 400 mg/kg of LTA upregulated the expression of T-bet and Foxp3 proteins (p < 0.05), thus promoting the differentiation of jejunum CD4+ T cells to Th1 and Tregs and increasing the cytokines IFN-γ, IL-10, and TGF-ß (p < 0.05). We found that 200 and 400 mg/kg of LTA downregulated the expression of RORγt and GATA3, thus inhibiting the differentiation of Th2 and Th17 cells and decreasing cytokines IL-4, IL-5, IL-13 TNF-α, IL-6, and IL-17A (p < 0.05). LTA inhibited the degranulation of mast cells and significantly decreased the serum levels of OVA-IgE, HIS, and mouse MCPT-1 (p < 0.05). Therefore, LTA intervention alleviated OVA allergy by improving intestine-specific immunity.

The atomic-level regulation of single-atom site catalysts for the electrochemical CO2 reduction reaction.

The electrochemical CO2 reduction reaction (CO2RR) is viewed as a promising way to remove the greenhouse gas CO2 from the atmosphere and convert it into useful industrial products such as methane, methanol, formate, ethanol, and so forth. Single-atom site catalysts (SACs) featuring maximum theoretical atom utilization and a unique electronic structure and coordination environment have emerged as promising candidates for use in the CO2RR. The electronic properties and atomic structures of the central metal sites in SACs will be changed significantly once the types or coordination environments of the central metal sites are altered, which appears to provide new routes for engineering SACs for CO2 electrocatalysis. Therefore, it is of great importance to discuss the structural regulation of SACs at the atomic level and their influence on CO2RR activity and selectivity. Despite substantial efforts being made to fabricate various SACs, the principles of regulating the intrinsic electrocatalytic performances of the single-atom sites still needs to be sufficiently emphasized. In this perspective article, we present the latest progress relating to the synthesis and catalytic performance of SACs for the electrochemical CO2RR. We summarize the atomic-level regulation of SACs for the electrochemical CO2RR from five aspects: the regulation of the central metal atoms, the coordination environments, the interface of single metal complex sites, multi-atom active sites, and other ingenious strategies to improve the performance of SACs. We highlight synthesis strategies and structural design approaches for SACs with unique geometric structures and discuss how the structure affects the catalytic properties.

Atomic-Level Modulation of Electronic Density at Cobalt Single-Atom Sites Derived from Metal-Organic Frameworks: Enhanced Oxygen Reduction Performance.

Demonstrated here is the correlation between atomic configuration induced electronic density of single-atom Co active sites and oxygen reduction reaction (ORR) performance by combining density-functional theory (DFT) calculations and electrochemical analysis. Guided by DFT calculations, a MOF-derived Co single-atom catalyst with the optimal Co1 -N3 PS active moiety incorporated in a hollow carbon polyhedron (Co1 -N3 PS/HC) was designed and synthesized. Co1 -N3 PS/HC exhibits outstanding alkaline ORR activity with a half-wave potential of 0.920 V and superior ORR kinetics with record-level kinetic current density and an ultralow Tafel slope of 31 mV dec-1 , exceeding that of Pt/C and almost all non-precious ORR electrocatalysts. In acidic media the ORR kinetics of Co1 -N3 PS/HC still surpasses that of Pt/C. This work offers atomic-level insight into the relationship between electronic density of the active site and catalytic properties, promoting rational design of efficient catalysts.