Regulating the Coordination Environment of MOF‐Templated Single‐Atom Nickel Electrocatalysts for Boosting CO₂ Reduction

Abstract

The general synthesis and control of the coordination environment of single-atom catalysts (SACs) remains ag reat challenge.H erein, ag eneral host-guest cooperative protection strategy has been developed to construct SACs by introducing polypyrrole (PPy) into abimetallic metal-organic framework. As an example,the introduction of Mg 2+ in MgNi-MOF-74 extends the distance between adjacent Ni atoms;t he PPy guests serve as Nsource to stabilizethe isolated Ni atoms during pyrolysis.Asaresult, aseries of single-atom Ni catalysts (named Ni SA -N x -C) with different Nc oordination numbers have been fabricated by controlling the pyrolysis temperature. Significantly,t he Ni SA -N 2 -C catalyst, with the lowest N coordination number,a chieves high CO Faradaic efficiency (98 %) and turnover frequency (1622 h À1 ), far superior to those of Ni SA -N 3 -C and Ni SA -N 4 -C,inelectrocatalytic CO 2 reduction. Theoretical calculations reveal that the low Nc oordination number of single-atom Ni sites in Ni SA -N 2 -C is favorable to the formation of COOH* intermediate and thus accounts for its superior activity.Single-atom catalysts (SACs), featured with metal atoms dispersed at atomic level, can achieve amaximal utilization of metal atoms and have demonstrated excellent catalytic performance for various reactions. [1] Combining the merits of both heterogeneous and homogenous catalysts,SACshave been regarded as akind of unique heterogeneous catalysts to serve as an ideal model for the exploration of structureproperty relationships during reaction processes. [2] Theatomically dispersed metal atoms of SACs are stabilized by the support through coordination interaction to minimize their surface energy.T herefore,t he local coordination environ-ment usually plays asignificant role for both catalytic activity and selectivity of SACs.A lthough much work has been devoted in this field, to our knowledge,accurate control over the coordination environment of SACs at an atomic level remains agreat challenge and has been rarely investigated. [3] Metal-organic frameworks (MOFs), ac lass of crystalline porous materials with well-defined structures and diverse compositions,n ot only exhibit great potentials for applications in diverse fields, [4] but also are promising precursors to produce desired materials for energy and catalysis. [5] Particularly,MOFs have recently emerged as an ideal platform for the construction of SACs,a st he targeted metal atoms in MOFs can be rationally and spatially separated in an atomically dispersed form. [6] More specifically,b ecause of the precisely designable and tailorable structures and components in MOFs,i ti sc onvenient to realize coordination environment regulation of SACs based on MOFs. [3b,c] While great progress has been achieved, the currently available strategies towards MOF-based SACs are limited to MOFs involving abundant Na toms,s uch as ZIFs [3b,c, 6c,d, 7] and porphyrinic MOFs. [8] Given that Na toms are not involved in most MOFs,itishighly desired to develop amore general approach for the ...

Transition metal-based catalysts for the electrochemical CO2reduction: from atoms and molecules to nanostructured materials

“…More recently, a general host-guest cooperative protection strategy based on the introduction of polypyrrole into bimetallic MgNi-MOF-74, followed by a pyrolysis step, allowed to obtain Ni SACs with tunable N/C coordination by controlling the annealing temperature. 319 The hybrid Ni SA -N 2 -C material with the lowest N coordination number (2) showed the best performance across the series, affording a maximum FE CO 98% at À0.8 V vs. RHE. By using theoretical and experimental tools, Yamauchi and co-workers systematically investigated a series of hybrid Ni-N x C 4Àx (x = 0-4) moieties containing different combinations of coordinating N or C atoms in an attempt to elucidate the role of C atoms on the structural and catalytic properties of Ni N-C SACs.…”

Ionic Exchange of Metal−Organic Frameworks for Constructing Unsaturated Copper Single‐Atom Catalysts for Boosting Oxygen Reduction Reaction

“…In the powder X‐ray diffraction patterns, only one broad peak in the range of 20°–30° could be observed (Figure S7, Supporting Information), corresponding to the (002) planes of carbon. [ 18 ] No Cu characteristic peaks could be observed in Cu SAs/NC materials, indicating the poor crystallinity of Cu. Figure S8, Supporting Information, shows the survey scan X‐ray photoelectron spectroscopy (XPS) spectra of Cu SAs/NC materials.…”

“…[ 22 ] Such a phenomenon was also observed in the study of atomically dispersed NiNC materials, in which the interatomic distance of NiN for NiN 3 was slightly decreased compared with NiN 4 . [ 18 ] Under higher temperature, we supposed that partial of nitrogen was removed, resulting in the formation of Cu SAs/NC with CuN 3 moieties (Figure 2G). In this case, the valence state of Cu atoms was slightly decreased, due to the loss of one‐nitrogen coordination.…”

Single-atom Fe with Fe1N3 structure showing superior performances for both hydrogenation and transfer hydrogenation of nitrobenzene

“…Single-atom catalysis has become one of the most active research frontiers in heterogeneous catalysis due to the uniform active site and total atom utilization efficiency [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. The uniform active site can provide an ideal platform for deeper understanding of the fundamentals.…”