Enhanced photoelectrochemical hydrogenation of green-house gas CO2 to high-order solar fuel on coordinatively unsaturated metal-N sites containing carbonized Zn/Co ZIFs
Introduction
Fossil fuel shortage and global warming are the two major concerns in modern society. The fixation of CO2 via the photoelectrochemical reduction in a photoelectrochemical cell (PEC) [1], which is also known as artificial photosynthesis, has received a considerable attention for its application in the CO2 reduction recently [2], [3]. Among various options for CO2 conversion and utilization, CO2 hydrogenation to alcohol fuels [4], [5] (methanol, ethanol and propanol) has been considered as the favorite since these alcohol fuels can be easily transported and used as fuel or as an intermediate to produce valuable chemicals. Intense research effort has been made towards CO2 hydrogenation to alcohol fuels. However, achieving a high product selectivity towards the production of high-order alcohol fuels (ethanol and propanol) is still challenging.
Nowadays, various cathode catalysts, including Cu, Zn, graphene, ZIF, and MOF [6], [7], [8], [9], [10] have been investigated to be used in the CO2 photoelectrochemical reduction reaction (CO2PRR) to generate valuable products. However, the development of efficient and high-selective CO2PRR catalysts, which are able to activate the inert CO2 molecule into high-order liquid fuels at low overpotential or even spontaneously, remains a challenge.
Among the potential candidates, transition metal complexes based on nitrogen-donor ligand catalysts have attracted a large attention [11]. N-doping can effectively alter the catalyst electronic and geometrical properties and thus improve its catalytic activity [11], [12]. The change of these properties of the catalysts will lead to the stronger bonding of intermediates on the surface, resulting in the much easier generation of high-order products [13]. N-doping can be effectively achieved either by etching the carbon material in a nitrogen-containing gas or via the direct pyrolysis of N-containing carbon sources, such as ZIFs and MOFs [14], [15]. In both methods, the pyrolysis conditions are known to have a significant effect on the composition and on the structure of the resultant catalysts. The structure changes can have large impact on the activity of the catalysts in CO2PRR.
Herein, a strategy to facilitate the CO2PRR via the construction of coordinatively unsaturated transition metal-nitrogen active sites [11], [16], [17], [18] within porous carbon, derived from the pyrolysis of the Zn/Co bimetallic Zeolitic Imidazolate Framework (Zn/Co ZIF) is proposed. Moreover, this technique is used to reduce CO2 in a photoeletrochemical cell for the first time. The effects of the applied biases and of the pyrolysis duration were studied by placing the carbonized Zn/Co ZIF (C–Zn/Co ZIF) samples in the PEC system. DFT calculations were also performed to understand the high catalytic activity and the selectivity of the catalyst for the CO2PRR.
Section snippets
Materials
The analytical grade chemicals were used without any further purification. Zn(NO3)2·6H2O, Co(NO3)2·6H2O, NH4F, NaHCO3, NaCl, absolute ethanol, ethylene glycol, and isopropanol were purchased from Sinopharm Chemical Reagent Co. Ltd (China). 2-methylimidazole was purchased from Sigma Aldarich Co. Ltd. The Nafion 117 membrane and the Nafion membrane solution were purchased from Shanghai Hesen Co. Ltd. The copper foam (CF, 100 ppi) was purchased from Taili Suzhou Co. Ltd., and the 99.89% Ti foil
Catalyst structure and morphology
The XRD patterns of the Zn/Co ZIF and of the three C–Zn/Co ZIF catalysts were obtained. According to Fig. 1, the XRD pattern of the Zn/Co ZIF (Fig. 1(a)) shows similar characteristic peaks as ZIF-8, indicating that the Zn/Co ZIF and the ZIF-8 have a similar crystal structure [9], [23]. The XRD patterns of the C–Zn/Co ZIFs (Fig. 1(b)) show diffraction peaks located at 2θ = 31.8, 34.5, 36.3, 47.6, 56.7, 62.8, and 68°. These peaks have been attributed to ZnO. While the XRD patterns of the
Conclusions
In summary, carbon-based Zn/Co ZIF (C–Zn/Co) catalysts with various pyrolysis durations were successfully synthesized by pyrolyzing the pristine Zn/Co ZIF in an N2 atmosphere. Moreover, the CO2 photoelectrochemical reduction reaction at ambient temperature for these compounds was achieved for the first time. The XPS measurement shows that several coordinatively unsaturated Co–N sites can be formed upon the increase of the pyrolysis duration, and this greatly affectes the catalyst activity. The
Acknowledgements
This study was supported by the National Natural Science Foundation of China (51676171), National Key Technologies Research and Development Program-China (2016YFE0117900).
References (32)
- et al.
Photoelectrochemical reduction of CO2 on Cu/Cu2O films: product distribution and pH effects
Chem Eng J
(2015) - et al.
CO2 hydrogenation to methanol over Pd/In2O3: effects of Pd and oxygen vacancy
Appl Catal B Environ
(2017) - et al.
MOFs based on ZIF-8 deposited on TiO2 nanotubes increase the surface adsorption of CO2 and its photoelectrocatalytic reduction to alcohols in aqueous media
Appl Catal B Environ
(2018) - et al.
Enhanced photocatalytic conversion of greenhouse gas CO2 into solar fuels over g-C3N4 nanotubes with decorated transparent ZIF-8 nanoclusters
Appl Catal B Environ
(2017) - et al.
Selective photocatalytic reduction of CO2 into CH4 over Pt-Cu2O TiO2 nanocrystals: the interaction between Pt and Cu2O cocatalysts
Appl Catal B Environ
(2017) - et al.
Creating coordinatively unsaturated metal sites in metal-organic-frameworks as efficient electrocatalysts for the oxygen evolution reaction: insights into the active centers
Nano Energy
(2017) - et al.
Comprehensive study of ultra-microporous nitrogen-doped activated carbon for CO2 capture
Carbon
(2015) - et al.
Hierarchically porous N-doped carbon derived from ZIF-8 nanocomposites for electrochemical applications
Electrochim Acta
(2016) - et al.
Designed synthesis of nitrogen-rich carbon wrapped Sn nanoparticles hybrid anode via in-situ growth of crystalline ZIF-8 on a binary metal oxide
Nano Energy
(2016) - et al.
Selective reduction of CO2 to alcohol products on octahedral catalyst of carbonized Cu(BTC) doped with Pd nanoparticles in a photoelectrochemical cell
Chem Eng J
(2019)
Preparation and carbon dioxide uptake capacity of N-doped porous carbon materials derived from direct carbonization of zeolitic imidazolate framework
Carbon
Superhigh surface area determination of microporous solids
Colloids Surface
Metal–organic framework (MOF) as a template for syntheses of nanoporous carbons as electrode materials for supercapacitor
Carbon
Photoelectrocatalytic reduction of CO2 into chemicals using Pt-modified reduced graphene oxide combined with Pt-modified TiO2 nanotubes
Environ Sci Technol
Photoelectrochemical reduction of CO2 in methanol with TiO2 photoanode and metal cathode
ECS Transactions
High-selectivity electrochemical conversion of CO2 to ethanol using a copper nanoparticle/N-doped graphene electrode
ChemistrySelect
Cited by (11)
Synergetic bimetallic catalysts: A remarkable platform for efficient conversion of CO<inf>2</inf> to high value-added chemicals
2023, Journal of Energy ChemistrySecondary metal doped cuprous-cyanoimidazole frameworks for triple-mode detection of dopamine
2023, Analytica Chimica ActaNanoarchitectonics of low-dimensional metal-organic frameworks toward photo/electrochemical CO<inf>2</inf> reduction reactions
2022, Journal of CO2 UtilizationCitation Excerpt :Due to the adjustable chemical composition [12,13], pore structure [14], and large specific surface area [15,16], MOFs have been widely used in various applications, such as catalysis, gas adsorption, drug delivery, energy storage, etc [15,17–21]. Furthermore, these attractive characteristics can increase the adsorption ability for CO2 and provide more catalytic active sites [22–26]. Nowadays, most of the studies on the application of MOFs for CO2 reduction were conducted on three-dimensional (3D) MOFs, but their catalytic activities are limited by the large thickness and small number of exposed active sites on the 3D MOF surface.
Bimetallic metal–organic frameworks and MOF-derived composites: Recent progress on electro- and photoelectrocatalytic applications
2022, Coordination Chemistry ReviewsCitation Excerpt :These include: (i) an improved light harvesting efficiency under visible light, (ii) an augmented photogenerated efficiency of charge separation by selecting proper organic ligands and metal ions for MOFs, and (iii) an optimized structure of photoelectrodes due to high tunability, synthetic adjustability, porosity, and CO2 adsorption ability of MOFs. A Zn/Co bimetallic MOF from a Zeolitic Imidazolate Framework family (Zn/Co ZIF) was used to synthesize a porous carbon-based composite (C-Zn/Co ZIFs) through a high-temperature pyrolysis process [243]. This composite was studied in a photoelectrochemical system (Fig. 27a), exhibiting an efficient reduction of CO2 at ambient temperature into various chemical products including CO, CH3OH, HCOOH, C2H5OH, CH3COOH, C3H7OH, and H2 (Fig. 27b).
Metal-organic frameworks and their derivatives-modified photoelectrodes for photoelectrochemical applications
2021, Coordination Chemistry ReviewsCitation Excerpt :Similarly, due to the 3D structure and high adsorption, copper foam is often used as a collector electrode [93]. In related research, Cheng and his colleagues [94] mixed C-Zn/Co-ZIF catalyst, Nafion and Deionized water (DI) together to coat on the foam copper. Copper foam was used as a 3D conductive support, which could uniformly disperse the C-Zn/Co-ZIF catalyst and effectively prevent the catalyst from agglomeration.