Enhancing CO2 Electroreduction with Au/Pyridine/Carbon Nanotubes Hybrid Structures

Multi-functionalized carbon nanotubes towards green fabrication of heterogeneous catalyst platforms with enhanced catalytic properties under NIR light irradiation

Metal/carbon nanotubes (CNTs) have been attractive hybrid systems due to their high specific surface area and exceptional catalytic activity, but their challenging synthesis and dispersion impede their extensive applications. Herein, we report a facile and green approach towards the fabrication of metal/CNT composites, which utilizes a versatile glycopeptide (GP) both as a stabilizer for CNTs in water and as a reducing agent for noble metal ions. The abundant hydrogen bonds in GP endow the formed GP-CNTs with excellent plasticity, enabling the availability of polymorphic CNT species from dispersion to viscous paste, gel, and even to dough by increasing their concentration. The GP molecules can reduce metal precursors at room temperature without additional reducing agents, enabling the in situ immobilization of metal nanoparticles (e.g. Au, Ag, Pt, and Pd) on the CNT surface. The combination of the excellent catalytic properties of Pd particles with photothermal conversion capability of CNTs makes the Pd/CNT composite a promising catalyst for the fast degradation of organic pollutants, as demonstrated by a model catalytic reaction using 4-nitrophenol (4-NP). The conversion of 4-NP using the Pd/CNT composite as the catalyst has increased by 1.6-fold under near infrared light illumination, benefiting from the strong light-to-heat conversion effect of CNTs. Our proposed strategy opens a new avenue for the synthesis of CNT composites as a sustainable and versatile catalyst platform.

CO2 Electrolysis via Surface-Engineering Electrografted Pyridines on Silver Catalysts

The electrochemical reduction of carbon dioxide (CO₂) to value-added materials has received considerable attention. Both bulk transition-metal catalysts and molecular catalysts affixed to conductive noncatalytic solid supports represent a promising approach toward the electroreduction of CO₂. Here, we report a combined silver (Ag) and pyridine catalyst through a one-pot and irreversible electrografting process, which demonstrates the enhanced CO₂ conversion versus individual counterparts. We find that by tailoring the pyridine carbon chain length, a 200 mV shift in the onset potential is obtainable compared to the bare silver electrode. A 10-fold activity enhancement at −0.7 V vs reversible hydrogen electrode (RHE) is then observed with demonstratable higher partial current densities for CO, indicating that a cocatalytic effect is attainable through the integration of the two different catalytic structures. We extended the performance to a flow cell operating at 150 mA/cm², demonstrating the approach’s potential for substantial adaptation with various transition metals as supports and electrografted molecular cocatalysts.

Regulation of electronic structures of MOF-derived carbon via ligand adjustment for enhanced Fenton-like reactions

Peroxymonosulfate (PMS)-based Fenton-like reactions are widely used for wastewater remediation. Metal-free carbonaceous activators can avoid the secondary pollution caused by metal leaching but often suffer from insufficient activity due to limited active centers and mass transfer barriers. Here, we prepared a series of heteroatom (N, S, F)-doped, highly porous carbonaceous materials (UC-X, X = N, S, F) by pyrolyzing UiO-66 precursors assembled by various organic ligands. Density functional theory calculations showed that the heteroatoms modulated the electronic structures of the carbon plane. UC-X exhibited significantly enhanced PMS activation capability compared with the undoped counterpart, in the efficiency order of UC-N > UC-S > UC-F > UC. UC-N (calcined at 1000°C) showed the best PMS activation, exceeding that of commonly used carbocatalysts. The prominent performance of UC-N originated from its unique porous structure and homogeneously dispersed graphitic N moieties. Trapping experiments and electron spin resonance showed a nonradical degradation pathway in the UC-N/PMS system, through which organics were oxidized by donating electrons to UC-N/PMS* metastable complexes. This work not only reports a universal way to access high-performance, metal-free PMS activators but also provides insight into the underlying mechanism of the carbon-activated PMS process.

Pyridine Grafted on SnO2 -Loaded Carbon Nanotubes Acting as Cocatalyst for Highly Efficient Electroreduction of CO2

Sn-based electrocatalysts have shown great potential in the future industrial application of CO₂ electroreduction (CO₂ ER) to C₁ products due to their non-toxicity and low price. However, it is a great challenge to fabricate a Sn-based electrocatalytic system with high performance and stability. Herein, grafted pyridine was innovatively coupled with SnO₂ to construct an organic-inorganic composite (SnO₂ /Py-CNTO) for highly efficient CO₂ ER. The detailed studies showed that pyridine and protonated pyridine coexist on the surface of SnO₂ /Py-CNTO, and both play distinctive roles in promoting the selectivity of CO₂ ER. Benefiting from the merits, SnO₂ /Py-CNTO delivered an excellent faradaic efficiency (FE) of 96 % for CO₂ ER at -1.29 V_RHE where the HCOOH production with 85 % FE dominated, and good stability for 32 h electrolysis. The theoretical calculations showed that protonated pyridine not only facilitates the CO₂ adsorption and HCOOH desorption, but also significantly reduces the limiting potential for the conversion of CO₂ to HCOOH.

A study on improving the current density performances of CO2 electrolysers

Electrochemical CO₂ reduction reaction (CO₂RR) technology can reduce CO₂ emission with converting excess electrical energy to high-value-added chemicals, which however needs further improvement on the electrolyser cell performance. In this work, extensive factors were explored in continuous CO₂ electrolysers. Gold, one of the benchmark materials for CO₂RR to produce CO, was used as the catalyst. Electrolyser configurations and membrane types have significant influences on cell performance. Compact MEA-constructed gas-phase electrolyser showed better catalytic performance and lower energy consumption. The gas diffusion electrode with a 7:1 mass ratio of total-catalyst-to-polytetrafluoroethylene (PTFE) ionomer exhibited the best performance. At a low total cell voltage of 2.2 V, the partial current density of CO production achieved 196.8 mA cm⁻², with 90.6% current efficiency and 60.4% energy efficiency for CO producing respectively. Higher CO selectivity can be achieved using anion exchange membranes, while higher selectivity for hydrogen and formate products can be achieved with cation exchange membranes. This research has pointed out a way on how to improve the CO₂RR catalytic performance in flow cells, leaving aside the characteristics of the catalyst itself.

Polyacrylamide-Mediated Silver Nanoparticles for Selectively Enhancing Electroreduction of CO2 towards CO in Water

Conversion of the greenhouse gas CO₂ to value-added products is an important challenge for sustainable energy research. Here, a durably nanohybrid composed of Ag nanoparticles and polyacrylamide was constructed for the selectively electroreduction of CO₂ to CO. The nanohybrid exhibited an outstanding CO faradaic efficiency of 97.2±0.2 % at -0.89 V_RHE (vs. the reversible hydrogen electrode) with a desirable CO partial current density of -22.0±2.3 mA cm^-2 and maintained the CO faradaic efficiency above 95 % over a wide potential range (-0.79 to -1.09 V_RHE ), showing excellent stability during a 48 h prolonged electrolysis. The origins of selective enhancement of CO₂ reduction over the nanohybrid stemmed from the activation of CO₂ via hydrogen bond and the low basicity of the amide. DFT calculations implied that the synergy of Ag nanoparticles and amide could better stabilize the key intermediate (*COOH) and effectively lower the overpotential of CO₂ reduction. These results establish the synergistic effects of organic/inorganic hybrid as a complementary method for tuning selectivity in CO₂ -to-fuels catalysis.

Inhibition of hydrogen evolution without debilitating electrochemical CO2 reduction via the local suppression of proton concentration and blocking of step-edges by pyridine functionalization on Cu electrocatalysts

HER suppression without debilitating CO₂RR by blocking step-edges and decreasing local H⁺ concentration on copper via pyridine functionalization.

Electrocatalysis for CO2 conversion: from fundamentals to value-added products

This timely and comprehensive review mainly summarizes advances in heterogeneous electroreduction of CO₂: from fundamentals to value-added products.

Transition metal-based catalysts for the electrochemical CO2 reduction: from atoms and molecules to nanostructured materials

An overview of the main strategies for the rational design of transition metal-based catalysts for the electrochemical conversion of CO₂, ranging from molecular systems to single-atom and nanostructured catalysts.

Porous Palladium Nanomeshes with Enhanced Electrochemical CO2 -into-Syngas Conversion over a Wider Applied Potential

Electrochemical conversion of CO₂ into syngas, which can be used directly in the classical petroleum industrial processes, provides a powerful approach for achieving the recycling of anthropogenic carbon. Pd has previously been reported to be capable of converting CO₂ into syngas with various CO/H₂ ratios, but only at limited applied potential, which is mainly attributed to fewer active sites exposed toward electrocatalysis. Herein, high-performance Pd nanomeshes (NMs) assembled with branch-like Pd nanoparticles were designed and synthesized by using a simple interface-induced self-assembly strategy; these NMs could catalyze CO₂ -into-syngas conversion with a high current density in a wide applied potential range from -0.5 to -1.0 V (vs. reversible hydrogen electrode). Further evidence validated that the enhanced activity of the Pd NMs was not only caused by the crosslinked network structure accelerating electron transport, but also by the greater number of edge and/or corner active sites exposed on the surface of the NMs, which facilitated CO₂ adsorption, CO₂ ^.- formation, COOH* stabilization, and CO generation. Under optimal operating conditions, Pd NMs could balance two competing reactions: CO₂ reduction and hydrogen evolution. The resultant syngases with the ideal and tunable CO/H₂ ratio between 0.5:1 and 1:1 could be used directly for methanol synthesis and Fischer-Tropsch reactions.