Reconstructing Cu Nanoparticle Supported on Vertical Graphene Surfaces via Electrochemical Treatment to Tune the Selectivity of CO2 Reduction toward Valuable Products

A vertical/horizontal graphene-based microneedle plant sensor for on-site detection of indole-3-acetic acid in vegetables

Plant hormones are important regulators of crop growth and production. In this study, an in situ electrochemical sensor was successfully built using flat microelectrodes with horizontally and vertically grown graphene to detect the plant regulator indole-3-acetic acid (IAA) in plants. Vertical and horizontal graphene layers were prepared by electron-assisted hot-filament chemical vapor deposition. Vertical graphene nanosheets were grown on a horizontal graphene layer as sensing electrodes, and a microneedle sensor was assembled by combining Pt and Ti microelectrodes. The vertical/horizontal graphene (VHG) microneedle sensor can rapidly detect IAA levels in various plants in situ over a wide pH range of 4.0-9.0 and concentration range of 1-100 μM, with a minimum detection limit of 0.21 μM (3σ/S). Subsequently, this microneedle sensor was used to determine the IAA content in different tissues of cucumber and cauliflower stems with satisfactory results. The combination of VHG microelectrode arrays and small electrochemical workstations is useful for constructing portable, low-cost, on-site, and fast electrochemical sensing platforms for plant growth monitoring.

Introducing La into a Customized Dual Cu Covalent Organic Framework to Steer CO2 Electroreduction Selectivity from C2H4 to CH4

Customizing multi-metal site catalysts for achieving controllable CO2 reduction reaction (CO2RR) product tuning holds immense promise yet poses formidable challenges. The traditional synthesis method of multi-metal sites is the pyrolysis of metal-containing precursors, which is inherently uncontrollable. Herein, a bottom-up strategy is employed to customize and synthesize multi-metal sites in covalent organic frameworks (COFs), aiming to controllably switch the CO2 reduction selectivity by regulating the electronic structure of active sites. Briefly, La element provides chances for manipulating and finetuning the electronic structure of the customized dual Cu sites, and converts the main catalytic product of CO2RR from ethylene to methane. Density functional theory calculations show that the introduction of La alters the electronic structure around Cu, enhances CO2 and H2O activation, and changes the formation of energy barriers of key intermediates. To the best of the author's knowledge, this study constructed the first example of customized multi-metal site COF catalysts and provided new ideas for controllable modulation of products.

State of Play of Critical Mineral-Based Catalysts for Electrochemical E-Refinery to Synthetic Fuels

The pursuit of decarbonization involves leveraging waste CO2 for the production of valuable fuels and chemicals (e.g., ethanol, ethylene, and urea) through the electrochemical CO2 reduction reactions (CO2RR). The efficacy of this process heavily depends on electrocatalyst performance, which is generally reliant on high loading of critical minerals. However, the supply of these minerals is susceptible to shortage and disruption, prompting concerns regarding their usage, particularly in electrocatalysis, requiring swift innovations to mitigate the supply risks. The reliance on critical minerals in catalyst fabrication can be reduced by implementing design strategies that improve the available active sites, thereby increasing the mass activity. This review seeks to discuss and analyze potential strategies, challenges, and opportunities for improving catalyst activity in CO2RR with a special attention to addressing the risks associated with critical mineral scarcity. By shedding light onto these aspects of critical mineral-based catalyst systems, this review aims to inspire the development of high-performance catalysts and facilitates the practical application of CO2RR technology, whilst mitigating adverse economic, environmental, and community impacts.

Ru-Induced Defect Engineering in Co3O4 Lattice for High Performance Electrochemical Reduction of Nitrate to Ammonium

Amidst these growing sustainability concerns, producing NH4 + via electrochemical NO3 - reduction reaction (NO3RR) emerges as a promising alternative to the conventional Haber-Bosch process. In a pioneering approach, this study introduces Ru incorporation into Co3O4 lattices at the nanoscale and further couples it with electroreduction conditioning (ERC) treatment as a strategy to enhance metal oxide reducibility and induce oxygen vacancies, advancing NH4 + production from NO3RR. Here, supported by a suite of ex situ and in situ characterization measurements, the findings reveal that Ru enrichment promotes Co species reduction and oxygen vacancy formation. Further, as evidenced by the theoretical calculations, Ru integration lowers the energy barrier for oxygen vacancy formation, thereby facilitating a more energy-efficient NO3RR-to-NH4 + pathway. Optimal catalytic activity is realized with a Ru loading of 10 at.% (named 10Ru/Co3O4), achieving a high NH4 + production rate (98 nmol s-1 cm-2), selectivity (97.5%) and current density (≈100 mA cm-2) at -1.0 V vs RHE. The findings not only provide insights into defect engineering via the incorporation of secondary sites but also lay the groundwork for innovative catalyst design aimed at improving NH4 + yield from NO3RR. This research contributes to the ongoing efforts to develop sustainable electrochemical processes for nitrogen cycle management.

Recent advances in dynamic reconstruction of electrocatalysts for carbon dioxide reduction

Electrocatalysts undergo structural evolution under operating electrochemical CO2 reduction reaction (CO2RR) conditions. This dynamic reconstruction correlates with variations in CO2RR activity, selectivity, and stability, posing challenges in catalyst design for electrochemical CO2RR. Despite increased research on the reconstruction behavior of CO2RR electrocatalysts, a comprehensive understanding of their dynamic structural evolution under reaction conditions is lacking. This review summarizes recent developments in the dynamic reconstruction of catalysts during the CO2RR process, covering fundamental principles, modulation strategies, and in situ/operando characterizations. It aims to enhance understanding of electrocatalyst dynamic reconstruction, offering guidelines for the rational design of CO2RR electrocatalysts.

Polymer Modification Strategy to Modulate Reaction Microenvironment for Enhanced CO2 Electroreduction to Ethylene

Modulation of the microenvironment on the electrode surface is one of the effective means to improve the efficiency of electrocatalytic carbon dioxide reduction (eCO2 RR). To achieve high conversion rates, the phase boundary at the electrode surface should be finely controlled to overcome the limitation of CO2 solubility in the aqueous electrolyte. Herein, we developed a simple and efficient method to structure electrocatalyst with a superhydrophobic surface microenvironment by one-step co-electrodeposition of Cu and polytetrafluoroethylene (PTFE) on carbon paper. The super-hydrophobic Cu-based electrode displayed a high ethylene (C2 H4 ) selectivity with a Faraday efficiency (FE) of 67.3 % at -1.25 V vs. reversible hydrogen electrode (RHE) in an H-type cell, which is 2.5 times higher than a regular Cu electrode without PTFE. By using PTFE as a surface modifier, the activity of eCO2 RR is enhanced and water (proton) adsorption is inhibited. This strategy has the potential to be applied to other gas-conversion electrocatalysts.

Ultrafine ZnCo2O4 QD-incorporated carbon nitride mediated peroxymonosulfate activation for norfloxacin oxidation: performance, mechanisms and pathways

Recently, peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) are being actively investigated as a potential technology for water decontamination and many efforts have been made to improve the activation efficiency of PMS. Herein, a 0D metal oxide quantum dot (QD)-2D ultrathin g-C3N4 nanosheet (ZnCo2O4/g-C3N4) hybrid was facilely fabricated through a one-pot hydrothermal process and used as an efficient PMS activator. Benefiting from the restricted growth effect of the g-C3N4 support, ultrafine ZnCo2O4 QDs (∼3-5 nm) are uniformly and stably anchored onto the surface. The ultrafine ZnCo2O4 possesses high specific surface areas and shortened mass/electron transport route so that the internal static electric field (Einternal) formed in the interface between p-type ZnCo2O4 and the n-type g-C3N4 semiconductor could speed up the electron transfer during the catalytic reaction. This thereby induces the high-efficiency PMS activation for rapid organic pollutant removal. As expected, the ZnCo2O4/g-C3N4 hybrid catalysts significantly outperformed individual ZnCo2O4 and g-C3N4 in catalytic oxidative degradation of norfloxacin (NOR) in the presence of PMS (95.3% removal of 20 mg L-1 of NOR in 120 min). Furthermore, the ZnCo2O4/g-C3N4-mediated PMS activation system was systematically studied in terms of the identification of reactive radicals, the impact of control factors, and the recyclability of the catalyst. The results of this study demonstrated the great potential of a built-in electric field-driven catalyst as a novel PMS activator for the remediation of contaminated water.

Single-Site Metal-Organic Framework and Copper Foil Tandem Catalyst for Highly Selective CO2 Electroreduction to C2 H4

Tandem catalysis is a promising way to break the limitation of linear scaling relationship for enhancing efficiency, and the desired tandem catalysts for electrochemical CO₂ reduction reaction (CO₂ RR) are urgent to be developed. Here, a tandem electrocatalyst created by combining Cu foil (CF) with a single-site Cu(II) metal-organic framework (MOF), named as Cu-MOF-CF, to realize improved electrochemical CO₂ RR performance, is reported. The Cu-MOF-CF shows suppression of CH₄ , great increase in C₂ H₄ selectivity (48.6%), and partial current density of C₂ H₄ at -1.11 V versus reversible hydrogen electrode. The outstanding performance of Cu-MOF-CF for CO₂ RR results from the improved microenvironment of the Cu active sites that inhibits CH₄ production, more CO intermediate produced by single-site Cu-MOF in situ for CF, and the enlarged active surface area by porous Cu-MOF. This work provides a strategy to combine MOFs with copper-based electrocatalysts to establish high-efficiency electrocatalytic CO₂ RR.

Atomically Dispersed Cu Catalysts on Sulfide-Derived Defective Ag Nanowires for Electrochemical CO2 Reduction

Single-atom catalysts (SACs) have shown potential for achieving an efficient electrochemical CO₂ reduction reaction (CO2RR) despite challenges in their synthesis. Here, Ag₂S/Ag nanowires provide initial anchoring sites for Cu SACs (Cu/Ag₂S/Ag), then Cu/Ag(S) was synthesized by an electrochemical treatment resulting in complete sulfur removal, i.e., Cu SACs on a defective Ag surface. The CO2RR Faradaic efficiency (FE_CO2RR) of Cu/Ag(S) reaches 93.0% at a CO2RR partial current density (j_CO2RR) of 2.9 mA/cm² under -1.0 V vs RHE, which outperforms sulfur-removed Ag₂S/Ag without Cu SACs (Ag(S), 78.5% FE_CO2RR with 1.8 mA/cm²j_CO2RR). At -1.4 V vs RHE, both FE_CO2RR and j_CO2RR over Cu/Ag(S) reached 78.6% and 6.1 mA/cm², which tripled those over Ag(S), respectively. As revealed by in situ and ex situ characterizations together with theoretical calculations, the interacted Cu SACs and their neighboring defective Ag surface increase microstrain and downshift the d-band center of Cu/Ag(S), thus lowering the energy barrier by ∼0.5 eV for *CO formation, which accounts for the improved CO2RR activity and selectivity toward related products such as CO and C₂₊ products.