Au-activated N motifs in non-coherent cupric porphyrin metal organic frameworks for promoting and stabilizing ethylene production.

Direct implementation of metal-organic frameworks as the catalyst for CO2 electroreduction has been challenging due to issues such as poor conductivity, stability, and limited > 2e- products. In this study, Au nanoneedles are impregnated into a cupric porphyrin-based metal-organic framework by exploiting ligand carboxylates as the Au3+ -reducing agent, simultaneously cleaving the ligand-node linkage. Surprisingly, despite the lack of a coherent structure, the Au-inserted framework affords a superb ethylene selectivity up to 52.5% in Faradaic efficiency, ranking among the best for metal-organic frameworks reported in the literature. Through operando X-ray, infrared spectroscopies and density functional theory calculations, the enhanced ethylene selectivity is attributed to Au-activated nitrogen motifs in coordination with the Cu centers for C-C coupling at the metalloporphyrin sites. Furthermore, the Au-inserted catalyst demonstrates both improved structural and catalytic stability, ascribed to the altered charge conduction path that bypasses the incoherent framework. This study underlines the modulation of reticular metalloporphyrin structure by metal impregnation for steering the CO2 reduction reaction pathway.

Promoting ethylene production over a wide potential window on Cu crystallites induced and stabilized via current shock and charge delocalization.

Electrochemical CO2 reduction (CO2RR) in a product-orientated and energy-efficient manner relies on rational catalyst design guided by mechanistic understandings. In this study, the effect of conducting support on the CO2RR behaviors of semi-conductive metal-organic framework (MOF) - Cu3(HITP)2 are carefully investigated. Compared to the stand-alone MOF, adding Ketjen Black greatly promotes C2H4 production with a stabilized Faradaic efficiency between 60-70% in a wide potential range and prolonged period. Multicrystalline Cu nano-crystallites in the reconstructed MOF are induced and stabilized by the conducting support via current shock and charge delocalization, which is analogous to the mechanism of dendrite prevention through conductive scaffolds in metal ion batteries. Density functional theory calculations elucidate that the contained multi-facets and rich grain boundaries promote C-C coupling while suppressing HER. This study underlines the key role of substrate-catalyst interaction, and the regulation of Cu crystalline states via conditioning the charge transport, in steering the CO2RR pathway.

Geometric Modulation of Local CO Flux in Ag@Cu2 O Nanoreactors for Steering the CO2 RR Pathway toward High-Efficacy Methane Production.

The electroreduction of carbon dioxide (CO2 RR) to CH4 stands as one of the promising paths for resourceful CO2 utilization in meeting the imminent "carbon-neutral" goal of the near future. Yet, limited success has been witnessed in the development of high-efficiency catalysts imparting satisfactory methane selectivity at a commercially viable current density. Herein, a unique category of CO2 RR catalysts is fabricated with the yolk-shell nanocell structure, comprising an Ag core and a Cu2 O shell that resembles the tandem nanoreactor. By fixing the Ag core and tuning the Cu2 O envelope size, the CO flux arriving at the oxide-derived Cu shell can be regulated, which further modulates the *CO coverage and *H adsorption at the Cu surface, consequently steering the CO2 RR pathway. Density functional theory simulations show that lower CO coverage favors methane formation via stabilizing the intermediate *CHO. As a result, the best catalyst in the flow cell shows a high CH4 Faraday efficiency of 74 ± 2% and partial current density of 178 ± 5 mA cm- 2 at -1.2 VRHE , ranking above the state-of-the-art catalysts reported today for methane production. These findings mark the significance of precision synthesis in tailoring the catalyst geometry for achieving desired CO2 RR performance.

Breaking the Linear Scaling Relationship by Compositional and Structural Crafting of Ternary Cu-Au/Ag Nanoframes for Electrocatalytic Ethylene Production.

Electrocatalytic conversion of carbon dioxide into high-value multicarbon (C2+ ) chemical feedstocks offers a promising avenue to liberate the chemical industry from fossil-resource dependence and eventually close the anthropogenic carbon cycle but is severely impeded by the lack of high-performance catalysts. To break the linear scaling relationship of intermediate binding and minimize the kinetic barrier of CO2 reduction reactions, ternary Cu-Au/Ag nanoframes were fabricated to decouple the functions of CO generation and C-C coupling, whereby the former is promoted by the alloyed Ag/Au substrate and the latter is facilitated by the highly strained and positively charged Cu domains. Thus, C2 H4 production in an H-cell and a flow cell occurred with high Faradic efficiencies of 69±5 and 77±2 %, respectively, as well as good electrocatalytic stability and material durability. In situ IR and DFT calculations unveiled two competing pathways for C2 H4 generation, of which direct CO dimerization is energetically favored.

Defect Engineering of Palladium-Tin Nanowires Enables Efficient Electrocatalysts for Fuel Cell Reactions.

The defect engineering of noble metal nanostructures is of vital importance because it can provide an additional yet advanced tier to further boost catalysis, especially for one-dimensional (1D) noble metal nanostructures with a high surface to bulk ratio and more importantly the ability to engineer the defect along the longitudinal direction of the 1D nanostructures. Herein, for the first time, we report that the defect in 1D noble metal nanostructures is a largely unrevealed yet essential factor in achieving highly active and stable electrocatalysts toward fuel cell reactions. The detailed electrocatalytic results show that the Pd-Sn nanowires (NWs) exhibit interesting defect-dependent performance, in which the defect-rich Pd4Sn wavy NWs display the highest activity and durability for both the methanol oxidation reaction (MOR) and the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations reveal that a large number of surface vacancies/agglomerated voids are the driving forces for forming surface grain boundaries (GBs) within Pd4Sn WNWs. These electronic active GB regions are the key factors in preserving the number of Pd0 sites, which are critical for minimizing the intrinsic site-to-site electron-transfer barriers. Through this defect engineering, the Pd4Sn WNWs ultimately yield highly efficient alkaline ORR and MOR. The present work highlights the importance of defect engineering in boosting the performance of electrocatalysts for potentially practical fuel cells and energy applications.

Octahedral gold-silver nanoframes with rich crystalline defects for efficient methanol oxidation manifesting a CO-promoting effect.

Three-dimensional bimetallic nanoframes with high spatial diffusivity and surface heterogeneity possess remarkable catalytic activities owing to their highly exposed active surfaces and tunable electronic structure. Here we report a general one-pot strategy to prepare ultrathin octahedral Au3Ag nanoframes, with the formation mechanism explicitly elucidated through well-monitored temporal nanostructure evolution. Rich crystalline defects lead to lowered atomic coordination and varied electronic states of the metal atoms as evidenced by extensive structural characterizations. When used for electrocatalytic methanol oxidation, the Au3Ag nanoframes demonstrate superior performance with a high specific activity of 3.38 mA cm-2, 3.9 times that of the commercial Pt/C. More intriguingly, the kinetics of methanol oxidation on the Au3Ag nanoframes is counter-intuitively promoted by carbon monoxide. The enhancement is ascribed to the altered reaction pathway and enhanced OH- co-adsorption on the defect-rich surfaces, which can be well understood from the d-band model and comprehensive density functional theory simulations.

Stabilizing and Activating Metastable Nickel Nanocrystals for Highly Efficient Hydrogen Evolution Electrocatalysis.

Exploring high-performance and cost-efficient electrocatalysts with unusual metastable phase offers opportunities for improving the electrochemical hydrogen generation, while it remains a great challenge to achieve them with desirable activity and stability. Herein, we report that the doping engineering in a metastable, hexagonal-close-packed nickel (hcp Ni) electrocatalyst is a largely unrevealed yet important factor in achieving an extremely active and stable electrocatalyst toward alkaline hydrogen evolution reaction (HER). Theoretical predications and experimental results suggest that, while the stability of metastable hcp Ni electrocatalyst can be largely improved via the manganese (Mn) doping due to the lower formation energy and lattice stabilization, the MnO/hcp Ni surface promotes the HER via intrinsic favorable H2O adsorption and fast water dissociation kinetics. Consequently, the Mn-doped hcp Ni electrocatalyst shows a small overpotential of 80 mV at 10 mA/cm2 and a low Tafel slope of 68 mV/dec. The result is even approaching that of the commercial Pt/C, being one of the best reported non-noble metal HER electrocatalysts in alkaline media. Under long-term chronopotentiometry measurement, such electrocatalyst can endure at least 10 h with negligible activity decay and structure change. The present work demonstrates the dimension in boosting the electrocatalysis by doping engineering of metastable electrocatalysts.

Encapsulating Microorganisms inside Electrospun Microfibers as a Living Material Enables Room-Temperature Storage of Microorganisms.

Room-temperature storage and transportation of microorganisms maximize the power of microorganisms in healthcare, energy, and environment. Recently, paper-based biotechnologies have been developed to enable room-temperature storage of a variety of nonliving biosystems such as diagnostic devices and cell-free systems. Herein, room-temperature storage of living microorganisms is realized by an electrospun nonwoven paper containing convex region, which is composed of coiled microfibers with dense distribution of microorganisms. Microorganisms are encapsulated into the microfibers and remain intact after electrospinning. Poly(ethylene oxide) is used as polymer matrix, and glycerol and dextran are used as additives. When the contents of glycerol and dextran are optimized as 5 and 0.4%, the room-temperature time is prolonged to 2 days, more than 8 folds as compared with the control group. Upon demand, the microorganisms can be activated by adding water and used for culturing microorganisms directly. Furthermore, mechanisms which account for microbial activity and storage are studied. Our microfiber-based strategy is universal for the room-temperature storage of prokaryotic and eukaryotic microorganisms in the solid formulation. Besides, our microorganism/polymer complex structures represent novel living materials via a bottom-up strategy, which are of great potential for new biomedical applications.