Zinc Imidazolate Metal–Organic Frameworks (ZIF‐8) for Electrochemical Reduction of CO₂ to CO

Abstract

Metal-organic frameworks (MOFs) are regardeda sp romising materials for CO 2 adsorption,which is an importantstep in CO 2 electrochemical reduction.I nt his work, zeolitic imidazolate framework (ZIF-8) nanomaterials were synthesized with various zinc sourcesa nd used as electrocatalystsf or CO 2 reduction to CO. Among them, ZIF-8,p repared using ZnSO 4 ,d elivers the best catalytic activity towards CO 2 electroreduction,w ith 65 % CO yield. The main catalytic centerc an be attributed to the discrete Zn nodes in ZIF-8. Electrolytes are important in increasingt he CO selectivity,a nd NaCl is the best suitablee lectrolyte duetof acile anion exchange.The increasing consumption of fossil resources is broadly regarded as ac ausef or the rising levels of CO 2 in the atmosphere, which leads to energy and environmental problems. [1][2][3] Electrochemical reduction of CO 2 ,u sing electricity from renewable resources, is ap otentially "clean"s trategy to obtain fuels and chemicals under mild conditions. [4][5][6][7][8] However, efficient and robust catalysts operatinga ts mall over-potentials with high selectivity and efficiency are still required for technology commercialization.To address these problems, av ariety of electrocatalysts based on metal and metallicc omplexesh as been developed. Amongt hem, noble metals,s uch as Au, [9,10] Ag, [11] and Pd, [12,13] have shown highF aradaic efficiencies for CO production;h owever,t he scarcity andh igh cost hinder their broad use in CO 2 electro-reduction. It is necessary to develop earth-abundant materials as potent catalysts for CO 2 electro-reduction. Metalorganic frameworks (MOFs)a re promising materials for diverse catalytic conversions. [14,15] Zeolitic imidazolate frameworks (ZIFs), as as ubclass of MOFs, are formed in zeolite topologies with metal ions and imidazolate ligands. [16] Due to their large specific surfacea rea, tunable porosity,a nd tailorable functionality,Z IFs emerged as versatile materials for catalysis,s eparation, energy storage, and so on. [17][18][19] Among various ZIFs, ZIF-8 have been further investigated ase lectrode materials fors upercapacitors, water electrolysis,p hotocatalysts, etc. [20][21][22][23] ZIF-8 served as porous electrode material for supercapacitora sr eported by Yamauchi et al, and delivered high electrochemical capacitance and good stability. [24] It can be calcined to form C, N-doped ZnO for use in dye degradationa nd water oxidation. [25] Besides, ZIF-8 possessesh igh CO 2 adsorption properties, which is an important step for CO 2 electrochemical reduction. [26] Recently,u sing MOFs for CO 2 reduction has just emerged and showed considerable catalytic performances. [28][29][30] Yet, ZIF-8 as ac atalysis material for CO 2 electrochemical reduction has not been reported.In this work, several ZIF-8 nanomaterials have been synthesized to investigate the aqueous electrocatalytic reduction of CO 2 ,e xploitingu nique properties such as larges urface area, uniform pore size, well-defined morphology,a nd strong coordination between me...

Metal–Organic Frameworks and Their Derived Materials as Electrocatalysts and Photocatalysts for CO2 Reduction: Progress, Challenges, and Perspectives

“…Moreover,t he amount of products in CR-MOF electrode is 13-fold greater than the Cu electrode at À1.2 Vv ersus SHE, which could result from the increasedp rotonc onductivity,e nhanced electronic conductivity, well-defined nanopores, and the high concentration of active sites of the as-prepared MOF-based electrocatalysts. [24] They found that ZIF-8 prepared using ZnSO 4 shows the highestp erformance with aC Oy ield of 65 %. [21] In their study,H KUST-1( [Cu 3 (m 6 -C 9 H 3 O 6 ) 2 ] n ), CuAdeAce ([Cu 3 (m 3 -C 5 H 4 N 5 ) 2 ] n ), CuDTAm esoporous metal-organic aerogel( MOA) ([Cu(m-C 2 H 2 N 2 S 2 )] n ), and CuZnDTAM OA ([Cu 0.6 Zn 0.4 (m-C 2 H 2 N 2 S 2 )] n )w ere synthesized and used for CO 2 reduction in the liquid electrolyte.…”

“…However,Z n-MOF-74 generatesb oth CO and H 2 with selectivities of 15.4 %a nd 78.3 %, respectively,a tÀ0.91 V versus RHE.Z IF-8 is another Zn-based MOF that has been widely investigated and shows potentiala pplications in various fields.W ang et al synthesized ZIF-8 nanoparticles using different Zn sources, such as ZnSO 4 ,Z n(NO 3 ) 2 ,a nd Zn(AC) 2 . [24] They found that ZIF-8 prepared using ZnSO 4 shows the highestp erformance with aC Oy ield of 65 %. Their study also elucidates that the actives ites may be discrete Zn nodes in ZIF-8.…”

Pristine Transition‐Metal‐Based Metal‐Organic Frameworks for Electrocatalysis

“…[164] Ni-MIL-77 NBs are successfully applied as a non-enzymatic glucose sensor in human serum with great stability, selectivity and detection limits. [171] They found that the discrete Zn nodes exerted a critical influence for high CO selectivity. [170] Zeolitic imidazolate frameworks (ZIFs), mainly composed of Zn or Co as metal ions, is a subclass of MOFs.…”

“…ZIF-8 a kind of Zn-MOFs is prepared with various zinc sources by Wang et al for carbon dioxide electrochemical reduction to carbon oxide. [171] They found that the discrete Zn nodes exerted a critical influence for high CO selectivity. In another study, Kang et al selected Zn-1,3,5-benzenetricarboxylic acid MOFs (designated as Zn-BTC MOFs) to be deposited on carbon paper (CP) and act as cathodes in the electrochemical reduction of carbon dioxide.…”

The Origin of the Electrocatalytic Activity for CO2 Reduction Associated with Metal‐Organic Frameworks

“…This group suggested that discrete Zn nodes are critical for high CO selectivity on the basis of comparing CO 2 RR activity with Co-ZIF and annealed Zn-ZIF. [10] However, a redox process involving Zn 2 + was observed during cyclic voltammetricm easurements. By contrast, in situ X-ray absorption spectroscopy measurements and density-functional theory calculations undertaken by Jiang et al suggested that the oxidation state of Zn centers in ZIFs remainu nchanged under catalytic turnover conditions.…”