Selective Electrocatalysts For CO2 Reduction Research Articles

In situ reconstructured alloy nanosheets heterojunction for highly selective electrochemical CO2 reduction to formate.

Tin (Sn)-based materials are expected to realize efficient CO2 electroreduction into formate. Herein, we constructed a heterojunction by depositing Cu on Cu-doped SnS2 nanosheets. During the electrochemical reaction, this heterojunction evolves to a highly active phase of Cu2O@Cu6Sn5 while maintaining its two-dimensional morphology. Specifically, a partial current density of 35 mA cm-2 with an impressive faradaic efficiency of 93% for formate production was achieved over the evolved heterojunction. In situ and ex situ experiments elucidated the formation mechanism of the Cu2O@Cu6Sn5 heterojunction. Cu6Sn5 nanosheets were formed via a stepwise desulfurization process, while Cu2O was generated through its reaction with hydroxyl radicals. This evolved heterojunction with a high electrochemically active surface area synergistically stabilized the *OCHO intermediate, thereby significantly enhancing the selectivity and activity. Our findings provide insight into the structural evolution process and guide the development of selective electrocatalysts for CO2 reduction.

Atomically Isolated Nickel–Nitrogen–Carbon Electrocatalysts Derived by the Utilization of Mg2+ ions as Spacers in Bimetallic Ni/Mg–Metal–Organic Framework Precursors for Boosting the Electroreduction of CO2

Electrochemical CO2 reduction (CO2R) is a promising avenue for the conversion of CO2 into fuels and beneficial chemicals. Significant efforts have been devoted to the development of active and selective electrocatalysts for CO2R. Atomically dispersed transition metal electrocatalysts have recently attracted consideration for CO2R due to their unique electronic and structural properties that can impart good catalytic performance and high active metal utilization. Among different precursors used for preparing these catalysts, metal–organic frameworks (MOFs) have been utilized as templates for generating atomically dispersed transition metal active sites as they provide well-defined structures that contain transition metals isolated from each other by organic ligands, along with high surface areas. However, maintaining the isolation of the transition metal species, achieving high surface concentrations of active sites, and imparting porosity during the high-temperature heat treatment of MOFs used during synthesis remain a challenge. In this report, Mg2+ ions have been employed as spacers in a bimetallic metal–organic framework (NiMg-MOF-74) to assist in preventing the coalescence of the Ni atoms into Ni-based particles during heat treatment, which combined with the use of urea as a nitrogen source resulted in the formation of isolated Ni–Nx/C active sites. Our findings demonstrated that Mg2+ ions play a crucial role in extending the distance between the adjacent Ni sites in the precursor structure and generating atomically isolated Ni sites. On the contrary, the utilization of Mg-free Ni-MOF-74 led to the formation of metallic Ni particles embedded in a carbon nanotube-based structure. Furthermore, we investigated the impact of pyrolysis temperature on the produced catalyst morphology. The generation of isolated Ni–Nx/C sites was promoted at higher pyrolysis temperatures (900 °C), while Ni-based particles were predominantly formed at a lower temperature (700 °C). The optimized atomically dispersed Ni–N–C catalyst exhibited excellent selectivity toward CO with a Faradaic efficiency of ∼90% and a current density of −4.2 mA/cm2 at −0.76 V vs a reversible hydrogen electrode.

Single-Ni Sites Embedded in Multilayer Nitrogen-Doped Graphene Derived from Amino-Functionalized MOF for Highly Selective CO2 Electroreduction

CO₂ electroreduction using renewable electricity is a promising pathway for CO₂ utilization. However, the development of highly active and selective catalysts for CO₂ reduction still poses significant challenges. Here, we report the use of an amino-functionalized metal–organic framework as a precursor to derive Ni-N-C active sites embedded in multilayer graphene shells as the dominant active sites for CO₂ electroreduction. During the process of high-temperature annealing and acid washing, the −NH₂ groups in the MOF precursors exhibit a greater tendency to generate structural defects on graphene layers and derive abundant Ni-N-C sites by Ni migration. Aggregated Ni particles, which incline to catalyze the competitive hydrogen evolution reaction, are successfully removed during the posttreatment, exposing numerous Ni-N-C active sites to facilitate the CO₂ electroreduction. The resulting catalyst displays excellent electrochemical CO₂ reduction activity to CO with Faradaic efficiencies above 90% in a wide range of potentials from −0.6 to −1.2 V versus reversible hydrogen electrode. The maximum Faradaic efficiency of 97% can be achieved at a low overpotential of 0.79 V with a CO partial current density of 27.2 mA cm–², which is among the best performance of Ni-based electrocatalysts reported so far. This work provides useful insights into the tuning of the metal sites by the coordination environment of MOFs toward the fabrication of highly active and selective electrocatalysts for CO₂ reduction.

Synergistic adsorption and activation of nickel phthalocyanine anchored onto ketjenblack for CO2 electrochemical reduction

Designing a facile and high-yield strategy to prepare highly active and selective electrocatalysts for CO2 reduction is beneficial to the industrial application. However, there are still many challenges in catalyst preparation. Besides, further mechanism studies on catalytic process for enhancing CO2 reduction are not clear. Herein, We have found that nickel phthalocyanine facilely incorporated into defect-rich ketjenblack by π-π stacking method can greatly improve its ECR performance. Nickel phthalocyanine/ketjenblack compounds show high selectivity and activity, 251 times turnover frequency for converting CO2 to CO compared to pristine nickel phthalocyanine, and keep above FECO of 90% under large potentials regions from −0.65 to −1.05 V vs RHE. Fundamentally density functional theory (DFT) calculations reveal that nickel phthalocyanine molecules anchored onto ketjenblack enhance the electron acceptability, decreasethe formation energy of the *COOH and inhibit the rival hydrogen evolution reaction (HER), thus showing extremely high synergistic catalytic properties in ECR.

Novel homogeneous selective electrocatalysts for CO2 reduction: an electrochemical and computational study of cyclopentadienyl-phenylendiamino-cobalt complexes

Cobalt cyclopentadienyl phenylendiamine complexes are revealed to be efficient and selective electrocatalysts for CO2 reduction, resulting in a 31-fold catalytic current without the hydrogen evolution.

Promoting electrocatalytic CO2 reduction to formate via sulfur-boosting water activation on indium surfaces

Electrocatalytic reduction of CO2 to fuels and chemicals is one of the most attractive routes for CO2 utilization. Current catalysts suffer from low faradaic efficiency of a CO2-reduction product at high current density (or reaction rate). Here, we report that a sulfur-doped indium catalyst exhibits high faradaic efficiency of formate (>85%) in a broad range of current density (25–100 mA cm−2) for electrocatalytic CO2 reduction in aqueous media. The formation rate of formate reaches 1449 μmol h−1 cm−2 with 93% faradaic efficiency, the highest value reported to date. Our studies suggest that sulfur accelerates CO2 reduction by a unique mechanism. Sulfur enhances the activation of water, forming hydrogen species that can readily react with CO2 to produce formate. The promoting effect of chalcogen modifiers can be extended to other metal catalysts. This work offers a simple and useful strategy for designing both active and selective electrocatalysts for CO2 reduction.

Electrochemical reduction of CO2 by single atom catalyst TM–TCNQ monolayers

Eight novel two-dimensional TM–TCNQ (TM = V–Zn) monolayers as highly efficient and selective electrocatalysts for CO2 reduction have been systematically studied and the underlying detailed reaction mechanisms have been revealed.

Correction: Biosynthesized silver nanorings as a highly efficient and selective electrocatalysts for CO2 reduction.

Correction for 'Biosynthesized silver nanorings as a highly efficient and selective electrocatalysts for CO2 reduction' by Yani Pan et al., Nanoscale, 2019, 11, 18595-18603.

Biosynthesized silver nanorings as a highly efficient and selective electrocatalysts for CO2 reduction.

Inspiration from nature has driven the development and applications of greener inorganic nanomaterials prepared using biotemplates in the field of nanoscience. In this study, we report the superiority of using a biosynthesized silver nanoring material for CO formation in CO2 saturated KHCO3. Compared to bulk silver and free silver nanoparticles prepared by pure chemical reduction, this silver nanoring (assembled on tobacco mosaic virus coat protein) exhibits significantly enhanced activity and selectivity for the conversion of CO2 to CO. The highest CO faradaic efficiency reaches 95.0% at an overpotential of 910 mV. Additionally, the CO partial current density is 2.7-fold higher than that of the free silver nanoparticles. We believe that the improved catalytic performance is related to the structuring ligand effect of the protein. The numerous functional groups on the protein may tune the reaction activity by influencing the binding energies of the intermediate species from CO2 reduction or hydrogen evolution.

Electrochemical Activation of CO2 through Atomic Ordering Transformations of AuCu Nanoparticles.

Precise control of elemental configurations within multimetallic nanoparticles (NPs) could enable access to functional nanomaterials with significant performance benefits. This can be achieved down to the atomic level by the disorder-to-order transformation of individual NPs. Here, by systematically controlling the ordering degree, we show that the atomic ordering transformation, applied to AuCu NPs, activates them to perform as selective electrocatalysts for CO2 reduction. In contrast to the disordered alloy NP, which is catalytically active for hydrogen evolution, ordered AuCu NPs selectively converted CO2 to CO at faradaic efficiency reaching 80%. CO formation could be achieved with a reduction in overpotential of ∼200 mV, and catalytic turnover was enhanced by 3.2-fold. In comparison to those obtained with a pure gold catalyst, mass activities could be improved as well. Atomic-level structural investigations revealed three atomic gold layers over the intermetallic core to be sufficient for enhanced catalytic behavior, which is further supported by DFT analysis.

A highly active nickel electrocatalyst shows excellent selectivity for CO2 reduction in acidic media

The development of selective electrocatalysts for CO2 reduction in water offers a sustainable route to carbon based fuels and feedstocks. However, molecular catalysts are typically studied in non-aqueous solvents, in part to avoid competitive H2 evolution. [Ni(cyclam)]2+ (1) is one of the few known electrocatalysts that operate in water and 30 years after its report its activity remains a rarely surpassed benchmark. Here we report that [Ni(cyclam-CO2H)]2+ (cyclam-CO2H = 1,4,8,11-tetraazacyclotetradecane-6-carboxylic acid (2)) shows greatly enhanced activity versus1 for CO production. At pHs < pKa of the pendant carboxylic acid a large increase in catalytic activity occurs. Remarkably, despite the high proton concentration (pH 2), 2 maintains selectivity for CO2 reduction and is believed to be unique in operating selectively in such acidic aqueous solutions.