"Two Ships in a Bottle" Design for Zn-Ag-O Catalyst Enabling Selective and Long-Lasting CO2 Electroreduction

Hydrophobic Electrode Design for CO2 Electroreduction in a Microchannel Reactor

Microchannel reactor is a novel electrochemical device to intensify CO₂ mass transfer with large interfacial areas. However, if the catalyst inserted in the microchannel is wetted, CO₂ is required to diffuse across the liquid film to get access to reaction sites. In this paper, a hydrophobic polytetrafluoroethylene (PTFE)-doped Ag nanocatalyst on a Zn rod was synthesized through a facile galvanic replacement of 2Ag⁺+Zn → 2Ag + Zn²⁺. The catalyst layer, which was PTFE incorporated into the Ag matrix, was detected to distribute uniformly on the Zn substrate with a thickness of 77 μm. Consequently, the PTFE-doped electrode demonstrated enhanced activity with an optimal 96.19% CO faradaic efficiency (FE_CO) in the microchannel reactor. Typically, the catalyst could maintain over 90% FE_CO even at the current density of 24 mA cm^-2, which was nearly 30% higher than that of a similar catalyst without PTFE. In addition, influences of the concentration of PTFE and deposition time were also investigated, determining that 1 vol % of PTFE and 30 min of coating yielded best electrocatalytic efficiency. To achieve a further breakthrough of CO₂ mass transfer limitations, reactions were applied under relatively high pressures (3-15 bar) in a single-compartment high-pressure cell. The maximum CO partial current density (j_CO) can reach 106.76 mA cm^-2 at 9 bar.

In-situ generation of In2O3 nanoparticles inside In[Co(CN)6] quasi-metal-organic-framework nanocubes for efficient electroreduction of CO2 to formate

Three-dimensional (3D) network structure of metal-organic framework (MOF) can accommodate outstanding electrocatalysis performances, but always collapse during the conversion to active materials or applications process. How to maintain the 3D network when producing active species is of great importance for full application of MOF. Herein, a new MOF material, In[Co(CN)₆] (In-Co PBA) nanocubes, are firstly synthesized. Through a controlled low-temperature deligandation process, the In-Co PBA nanocubes are transformed to a novel In₂O₃@In-Co PBA quasi-MOF nanocubes, which basically retain the 3D porous structure of PBA but with in situ generated In₂O₃ nanoparticles inside. When used as CO₂RR electrocatalyst, such a novel cubic composite structure exhibits excellent performances with faradaic efficiency of 85% for formate at a potential of -0.96 V and with current density of 31.5 mA·cm^-2 at -1.32 V, surpassing most of the reported indium-based catalysts. The excellent performance can be attributed to the special composite structure, which provides not only active sites by In₂O₃ nanoparticles to catalyze CO₂RR, but also the 3D porous framework by quasi-MOF to accelerate gaseous exchange and electrolyte permeation and prevent the electrode choking. This work offers a new strategy for the design of post-transition metal catalysts and the structure design of quasi-MOF.

Structure engineering of alveoli-like ZSM-5 with encapsulated Pt nanoparticles for the enhanced benzene oxidation

Inspired by the alveolar configuration, an alveoli-like ZSM-5 and the corresponding platinum encapsulated nanocomposite (Pt@PZ5) were fabricated via a dual-template method and a controlled selective desilication-recrystallization strategy. The dimensions of the central cavity, interconnected zeolitic vesicles, and mesoporous shell could be tuned by adjusting the synthesis parameters, as verified by scanning electron microscopy, transmission electron microscopy, nitrogen physisorption investigations, X-ray photoelectron spectroscopy, and X-ray diffraction techniques. Thanks to these properties and merits, the alveoli-like Pt@PZ5 showed the highest catalytic performance with excellent stability, obtaining 100% benzene conversion at 180 °C. Adsorption experiments combined with a finite-element simulation study uncovered that the alveolar architecture could expedite the accumulation of reactants and boost mass transfer; the conversion of intermediates in the voids could be further facilitated, giving optimal catalytic performance. Additionally, the alveolar architecture is resistant to metal sintering (5-20 nm) and leaching, even after calcination at 850 °C for 360 min. This work provides an alveolar concept into the rational design of efficient catalysts for fundamental catalytic action.

A Multiscale Strategy to Construct Cobalt Nanoparticles Confined within Hierarchical Carbon Nanofibers for Efficient CO2 Electroreduction

The efficiency of CO₂ electroreduction has been largely limited by the activity of the catalysts as well as the three-phase interface. Herein, a multiscale strategy is proposed to synthesize hierarchical nanofibers covered by carbon nanotubes and embedded with cobalt nanoparticles (Co/CNT/HCNF). The confinement effect of carbon nanotubes can restrict the diameter of the cobalt particles down to several nanometers and prevent the easy corrosion of these nanoparticles. The three-dimensional carbon nanofibers, in size range of several hundred nanometers, improve the electrochemically active surface area, facilitate electron transfer, and accelerate CO₂ transportation. These cross-linked carbon nanofibers eventually form a freestanding Co/CNT/HCNF membrane of dozens of square centimeters. Consequently, Co/CNT/HCNF produces CO with 97% faradaic efficiency at only -0.4 V_RHE cathode potential in an H-type cell. From the regulation of catalyst nanostructure to the design of macrography devices, Co/CNT/HCNF membrane can be directly used as the gas-diffusion compartment in a flow cell device. Co/CNT/HCNF membrane generates CO with faradaic efficiencies higher than 90% and partial current densities greater than 300 mA cm^-2 for at least 100-h stability. This strategy provides a successful example of efficient catalysts for CO₂ electroreduction and also has the feasibility in other self-standing energy conversion devices.

Design of Quasi-MOF Nanospheres as a Dynamic Electrocatalyst toward Accelerated Sulfur Reduction Reaction for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are considered as one of the most promising next-generation rechargeable batteries owing to their high energy density and cost-effectiveness. However, the sluggish kinetics of the sulfur reduction reaction process, which is so far insufficiently explored, still impedes its practical application. Metal-organic frameworks (MOFs) are widely investigated as a sulfur immobilizer, but the interactions and catalytic activity of lithium polysulfides (LiPs) on metal nodes are weak due to the presence of organic ligands. Herein, a strategy to design quasi-MOF nanospheres, which contain a transition-state structure between the MOF and the metal oxide via controlled ligand exchange strategy, to serve as sulfur electrocatalyst, is presented. The quasi-MOF not only inherits the porous structure of the MOF, but also exposes abundant metal nodes to act as active sites, rendering strong LiPs absorbability. The reversible deligandation/ligandation of the quasi-MOF and its impact on the durability of the catalyst over the course of the electrochemical process is acknowledged, which confers a remarkable catalytic activity. Attributed to these structural advantages, the quasi-MOF delivers a decent discharge capacity and low capacity-fading rate over long-term cycling. This work not only offers insight into the rational design of quasi-MOF-based composites but also provides guidance for application in Li-S batteries.

Preparation of trimetallic electrocatalysts by one-step co-electrodeposition and efficient CO2 reduction to ethylene

Use of multi-metallic catalysts to enhance reactions is an interesting research area, which has attracted much attention. In this work, we carried out the first work to prepare trimetallic electrocatalysts by a one-step co-electrodeposition process. A series of Cu–X–Y (X and Y denote different metals) catalysts were fabricated using this method. It was found that Cu₁₀La₁Cs₁ (the content ratio of Cu²⁺, La³⁺, and Cs⁺ in the electrolyte is 10 : 1 : 1 in the deposition process), which had an elemental composition of Cu₁₀La_0.16Cs_0.14 in the catalyst, formed a composite structure on three dimensional (3D) carbon paper (CP), which showed outstanding performance for CO₂ electroreduction reaction (CO₂RR) to produce ethylene (C₂H₄). The faradaic efficiency (FE) of C₂H₄ could reach 56.9% with a current density of 37.4 mA cm⁻² in an H-type cell, and the partial current density of C₂H₄ was among the highest ones up to date, including those over the catalysts consisting of Cu and noble metals. Moreover, the FE of C₂₊ products (C₂H₄, ethanol, and propanol) over the Cu₁₀La₁Cs₁ catalyst in a flow cell reached 70.5% with a high current density of 486 mA cm⁻². Experimental and theoretical studies suggested that the doping of La and Cs into Cu could efficiently enhance the reaction efficiency via a combination of different effects, such as defects, change of electronic structure, and enhanced charge transfer rate. This work provides a simple method to prepare multi-metallic catalysts and demonstrates a successful example for highly efficient CO₂RR using non-noble metals.

Trimetallic Cu₁₀La₁Cs₁ catalysts prepared via a one-step co-electrodeposition strategy can act as a robust electrocatalyst for CO₂RR to C₂H₄.

Accelerating Triple Transport in Zinc-Air Batteries and Water Electrolysis by Spatially Confining Co Nanoparticles in Breathable Honeycomb-Like Macroporous N-Doped Carbon

Rational engineering electrode structure to achieve an efficient triple-phase contact line is vital for applications such as in zinc-air batteries and water electrolysis. Herein, a facile "MOF-in situ-leaching and confined-growth-MOF" strategy is developed to construct a breathable trifunctional electrocatalyst based on N-doped graphitic carbon with Co nanoparticles spatially confined in an inherited honeycomb-like macroporous structure (denoted as Co@HMNC). The unique orderly arranged macroporous channels and the "ships in a bottle" confinement effect jointly expedite the triple transport, endowing the catalysts with fast reaction kinetics. As a result, the obtained Co@HMNC catalyst presents superb trifunctional performance with a positive half-wave potential (E_1/2 ) of 0.90 V for oxygen reduction reaction (ORR), and low overpotentials of 318 and 51 mV for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) at 10 mA cm^-2 , respectively. The Co@HMNC-based liquid Zn-air battery reaches a large specific capacity of 859 mA h g_Zn ^-1 , a high-power density of 198 mW cm^-2 , and long-term stability for 375 h, suggesting its promise for actual applications.