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Synthesis of Nanoporous Metals, Oxides, Carbides, and Sulfides: Beyond Nanocasting Wesley Luc and Feng Jiao* Center for Catalytic Science & Technology, Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware 19716, United States CONSPECTUS: Nanoporous metal-based solids are of particular interest because they combine a large quantity of surface metal sites, interconnected porous networks, and nanosized crystalline walls, thus exhibiting unique physical and chemical properties compared to other nanostructures and bulk counterparts. Among all of the synthetic approaches, nanocasting has proven to be a highly effective method for the syntheses of metal oxides with three-dimensionally ordered porous structures and crystalline walls. A typical procedure involves a thermal annealing process of a porous silica template filled with an inorganic precursor (often a metal nitrate salt), which converts the precursor into a desired phase within the silica pores. The final step is the selective removal of the silica template in either a strong base or a hydrofluoric acid solution. In the past decade, nanocasting has become a popular synthetic approach and has enabled the syntheses of a variety of nanoporous metal oxides. However, there is still a lack of synthetic methods to fabricate nanoporous materials beyond simple metal oxides. Therefore, the development of new synthetic strategies beyond nanocasting has become an important direction. This Account describes new progress in the preparation of novel nanoporous metal-based solids for heterogeneous catalysis. The discussion begins with a method called dealloying, an effective method to synthesize nanoporous metals. The starting material is a metallic alloy containing two or more elements followed by a selective chemical or electrochemical leaching process that removes one of the preferential elements, resulting in a highly porous structure. Nanoporous metals, such as Cu, Ag, and CuTi, exhibit remarkable electrocatalytic properties in carbon dioxide reduction, oxygen reduction, and hydrogen evolution reactions. In addition, the syntheses of metal oxides with hierarchical porous structures are also discussed. On the basis of the choice of hard template, nanoporous metal oxides with bimodal pore size distributions can be obtained. Combining nanocasting with chemical etching, a cobalt oxide with a hierarchical porous structure was synthesized, which possessed a surface area up to 250 m2 g−1, representing the highest surface area reported to date for nanoporous cobalt oxides. Lastly, this Account also covers the syntheses of nanoporous metal carbides and sulfides. The combination of in situ carburization and nanocasting enabled the syntheses of two ordered nanoporous metal carbides, Mo2C and W2C. For nanoporous metal sulfides, an “oxide-to-sulfide” synthetic strategy was proposed to address the large volume change issue of converting metal nitrate precursors to metal sulfide products in nanocasting. The successful syntheses of ordered nanoporous FeS2, CoS2, and NiS2 demonstrated the feasibility of the “oxide-to-sulfide” method. Concluding remarks include a summary of recent advances in the syntheses of nanoporous metalbased solids and a brief discussion of future opportunities in the hope of stimulating new interests and ideas. commonly labeled as “mesoporous” TiO2 based on the IUPAC definition. For consistency and simplicity, we use the term “nanoporous” instead of “mesoporous” or “macroporous” to describe solids with pore diameters of 2−100 nm in the following discussion. After the report of TiO2, nanoporous metal-based solids (primarily metal oxides) attracted significant attention because of their interesting electrochemical, catalytic, and magnetic properties.5−7 Among all of the synthetic methods, nanocasting, which uses a porous silica as a hard template to produce the replicated porous network, is the most widely used synthetic approach to fabricate nanoporous metal oxides with ordered porous structures.8−10 In some cases, this procedure was also labeled as “hard templating”. Since the first report of this nanocasting
1. INTRODUCTION Nanoporous solids have a large surface area, nanosized walls, and three-dimensionally porous networks, making them potential candidates for gas absorption, separation, and heterogeneous catalysis.1,2 In the past few decades, nanoporous solids, primarily silica-based zeolites, have been studied intensively as promising catalysts in the petroleum industry.1 Metals were often introduced to either the porous silica framework or the pore channels to enhance the catalytic performance. Attempts were also made to construct pure transition metal-based nanoporous solids by eliminating silica and alumina from the porous structures. However, these attempts proved to be very difficult due to the lack of a general synthetic method.3−5 In 1995, Ying et al. reported the first synthesis of a nanoporous transition metal oxide, TiO2, using alkyl(trimethyl)ammonium bromide surfactants.3 The assynthesized nanoporous TiO 2 contained 3 nm pores, © 2016 American Chemical Society
Received: February 29, 2016 Published: June 13, 2016 1351
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Figure 1. Typical SEM images for (a) nanoporous Au, (b) nanoporous Pd, (c) Al−Cu−Ti ternary alloy, and (d,e) nanoporous Cu−Ti.
Figure 2. (a) CO2 electrolysis results for bulk polycrystalline, nanoparticle, and nanoporous Ag at a constant overpotential of 0.49 V. (b) HER activities for Pt/C, np-CuTi, Ti-free np-Cu control sample, and polycrystalline Cu standard in 0.1 M KOH electrolyte.
such as electrochemical carbon dioxide reduction, hydrogen evolution reactions, oxygen evolution from water, and photocatalytic dye degradation.
concept in 2001, a wide range of ordered nanoporous metal oxides, such as Fe2O3, MnO2, Co3O4, Mn2O3, and NiO, have been synthesized.8−15 Because the porous structure of the resulting metal oxide replicates the porous structure of the silica template, designing a metal oxide with a desired porous structure is relatively easy compared to traditional softtemplating approaches. Another significant feature of nanocasted metal oxides is their well-ordered nature, which is in sharp contrast to the amorphous nature of nanoporous materials produced from soft-templating methods. More importantly, the nanoporous metal oxides exhibited unique properties compared to their bulk and nanoparticle counterparts.9 Although nanocasting is an effective method to synthesize nanoporous metal oxides, the range of materials that can be synthesized is still limited. Several technical barriers include (i) a lack of suitable metal precursors that can be converted into the desired phases through a simple thermal annealing process, (ii) stability issues of target materials in the presence of either a strong base or hydrofluoric acid, and (iii) large volume differences between precursors and target materials resulting in isolated nanoparticles rather than three-dimensional interconnected structures. For these challenges to be addressed, ideas beyond traditional nanocasting hold the key to new nanoporous metal-based solids that are not accessible using existing approaches. This Account discusses recent progress in the fabrication of nanoporous metal-based solids, including monometallic and bimetallic compounds, metal oxides with hierarchical porous structures, and ordered nanoporous metal carbides and sulfides. The resulting nanoporous materials showed superior catalytic properties in a variety of reactions,
2. DEALLOYING CREATING NANOPOROSITY IN METALS To date, the most effective approach to fabricate nanoporous metals is selective dealloying of a binary alloy.16,17 The removal of less noble metal leads to three-dimensional nanoporosity, which was first observed in the acid treatment of a Ag−Au alloy.18 This dealloying process is conceptually similar to the chemical leaching of silica template in nanocasting; both methods involve the removal of a substantial portion of the starting material to create porosity. In general, dealloying can be performed either chemically or electrochemically. In chemical dealloying, Al-based alloys are commonly used as the starting material because Al can be readily removed in either acids or bases. For example, Zhang et al. reported a generalized synthetic approach to fabricate nanoporous Au, Pd, Pt, Ag, and Cu through chemical dealloying of Al-based alloys (Figure 1a,b).19 Cu- and Znbased alloys are other alternative precursors to access nanoporous metals.20,21 It should be noted that the same approach can be extended to the syntheses of bimetallic materials by partial dealloying of binary alloys or fully dealloying ternary alloys. Lu et al. recently showed the synthesis of nanoporous Cu−Ti (denoted as np-CuTi) by chemically dealloying an Al−Cu−Ti ternary alloy.22 The ternary alloy consists of two separated phases, Al2Cu(Ti) and Al(Ti), which are evident in the SEM image (Figure 1c). After dealloying in 6 M KOH, a nanoporous Cu−Ti bimetallic 1352
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case, can possess distinctive properties such as high surface area, highly accessible pores, and enhanced mass transport capability. Sayler et al. reported a general nanocasting approach to synthesize Co3O 4 and NiO with hierarchically porous structures using a hierarchically porous silica as the hard template.38 A hierarchically porous structure can also be achieved by adding potassium salts in the synthesis of MnO2, resulting in a tetramodal micro-meso-macroporous structure.39 Another intriguing idea to create hierarchical porosity is to etch away portions of the nanopore walls. Figure 3 shows the overall
material with a hierarchical porous structure (Figure 1d,e) was obtained. The small pores (∼10−20 nm) were created from the removal of Al from the Al2Cu(Ti) phase, whereas the large pores (∼200−500 nm) were produced from leaching of the Al(Ti) phase. Because nanoporous metals are highly conductive, they are potential electrocatalyst candidates for a wide range of reactions, such as electrocatalytic hydrogen evolution, carbon dioxide reduction, hydrogenation, and hydrocarbon oxidation.16,17 Lu et al. recently showed that nanoporous Ag exhibited an exceptional activity that is over 3 orders of magnitude higher than that of a polycrystalline counterpart at a moderate overpotential of 1100 K) that exceeds the stability limit of mesoporous silica templates.44 For this issue to be addressed, new strategies are required to overcome the synthesis challenges associated with nanoporous metal carbides. 1354
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significantly different from metal oxides.51 In 1999, Braun et al. reported a general synthetic approach to prepare CdS, CdSe, and ZnS superlattices by direct templating in a lyotropic organic liquid crystal (Figure 7a,b).52 The resulting products
(Figure 5e, inset), which is likely due to the partial occupation of two independent sets of pore networks in the KIT-6 template. For nanoporous W2C, a similar bimodal distribution was observed; however, the 13 nm peak was much more pronounced (Figure 5f, inset), suggesting that the majority of W2C only grew in one set of pores. The difference in pore size distributions can be explained by the fact that (1) the density of W2C (∼16 g/cm3) is significantly higher than that of Mo2C (∼9 g/cm3) and (2) the mobility of W is poor compared to Mo during the crystal growth leading to difficulties for W2C to grow across both sets of pore networks. The catalytic properties of nanoporous metal carbides were investigated using anisole hydrodeoxygenation (HDO) as a model reaction. As-synthesized nanoporous W2C was pretreated in H2 at 723 K prior to the anisole HDO experiments. Remarkably, nanoporous W2C exhibited benzene selectivity in excess of 96% with negligible cyclohexane selectivity for anisole HDO at 443 K and atmospheric hydrogen pressure (Figure 6).46 The catalytic properties of nanoporous W2C are distinct
Figure 7. TEM images of (a)ZnS superlattice, (b) CdS superlattice, (c) nanoporous CdS, (d) nanoporous WS2, and (e) nanoporous MoS2. (f) Schematic diagram of the oxide-to-sulfide transformation that can be used to manage the large volume contraction that leads to isolated particles in a traditional nanocasting procedure.
contained 2−3 nm pores with a hexagonal symmetry. However, attempts to extend this method to other metal sulfides, such as Ag2S, CuS, HgS, and PdS, were not successful. Gao et al. showed the possibility to synthesize nanoporous CdS using a unique precursor, cadmium thioglycolate, and a nanocasting approach (Figure 7c).53 Although the synthesis successfully produced high-quality nanoporous CdS, the method required specific inorganic precursors. In 2007, the same group reported the syntheses of highly ordered nanoporous WS2 and MoS2 by combining the nanocasting approach with a high-temperature reductive sulfuration route (Figure 7d,e).54 The synthesis used H2S gas as the sulfurization source to convert the heteropoly acid precursors to WS2 and MoS2 crystallites inside the silica template. Although the report suggested the possibility to extend this method to other metal sulfides, the range of metal sulfides that can be synthesized was limited. A major challenge associated with nanocasting metal sulfides is the large volume change from metal precursor (e.g., a metal nitrate salt) to the final product.55 Taking iron sulfide as an example, every Fe atom in the Fe(NO3)3·9H2O precursor occupies a volume of 372 Å3, whereas the Fe atom in the FeS2 product only occupies 40 Å3, representing an order of magnitude difference in metal densities. Therefore, it is very difficult to form an interconnected, three-dimensionally continuous pore network using traditional nanocasting methods as the large volume shrinkage often results in isolated islands (Figure 7f). Although the large volume shrinkage also exists in the synthesis of metal oxide, the crystal formation mechanism is quite different. Recently, Sun et al. discovered the container effect in nanocasting.56 They proposed that the formation of metal oxides inside the silica template went through a dissolution-recrystallization process, leading to the growth of large, interconnected, crystalline oxides rather than isolated particles. However, the strategy cannot be applied to the synthesis of metal sulfides, as sulfidation occurs at relatively high temperatures.57,58 Additionally, the strong reactivity
Figure 6. Conversion and product selectivity of nanoporous W2C for anisole HDO. Feed = anisole 0.06 mol % in H2 at 131 kPa and 444 K with a total flow rate of ∼3.33 cm3 s−1.
from other HDO catalysts, such as MoO3,48 bimetallic FeMo phosphide catalysts,49 and Mo2C catalysts,50 representing the most selective anisole HDO catalyst for benzene synthesis under ambient hydrogen pressure and low reaction temperature. To date, the majority of nanoporous metal carbides that have been reported in the literature are semicarbides with a stoichiometric metal to carbon ratio close to two, such as Mo2C and W2C. However, there is interest in preparing metal carbides with a stoichiometric ratio of metal-to-carbon close to one. Although both Mo2C and W2C can be converted to MoC and WC at higher temperatures (∼1300 K), the syntheses pose a major challenge in nanocasting because the porous silica template not only collapses at such high temperatures but the silica template also reacts with carbon to form silicon carbide, which is hard to remove using a strong base or HF. New strategies to reduce the carburization temperature while controlling the metal-to-carbon stoichiometric ratio are required to access nanoporous high-temperature metal carbides.
5. AN “OXIDE-TO-SULFIDE” APPROACH TO NANOPOROUS METAL SULFIDES Metal sulfides are interesting materials for heterogeneous catalysis, solar cells, and batteries as their properties are 1355
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Accounts of Chemical Research between H2S or metal sulfides and nitrate precursors requires gas flow during synthesis, which drives away the acidic vapors that are critical for crystal growth through the dissolution and recrystallization mechanism. The large volume change between metal nitrate precursor and metal sulfide product can be addressed using an “oxide-tosulfide” strategy, which is outlined in Figure 7f.59 A metal oxide with a three-dimensionally continuous network is first formed inside a nanoporous silica template by taking advantage of the dissolution/recrystallization process. Then, the metal oxide network is transformed to sulfide through a H2S/sulfur vapor treatment at ∼400 °C.59 The density of Fe in α-Fe2O3 is 25.2 Å3/Fe, which is close to that in FeS2 (40 Å3/Fe), suggesting that instead of a volume contraction, the sulfidation conversion involves a small volume expansion to assist the formation of FeS2 with a continuous porous network. Because the majority of first-row transition metals share similar characteristics as iron, the “oxide-to-sulfide” approach can be adopted as a general strategy for the synthesis of various nanoporous metal sulfides. The proposed “oxide-to-sulfide” strategy was examined in the syntheses of FeS2, CoS2, and NiS2 with ordered porous structures. The highly ordered nanoporous structures are evident in the TEM images of all as-synthesized nanoporous metal sulfides (Figures 8a,c,e). The atomic structures of the
Figure 9. UV−vis spectra for nanoporous FeS2 in photocatalytic decomposition of methylene blue. Photographs of the reaction mixture at different reaction times clearly show the difference between nanoporous FeS2 and bulk FeS2 (inset).
crystal structure (Figure 9, inset). Similar behaviors also existed in nanoporous CoS2 and NiS2 samples, suggesting the significance of nanoporosity.
6. SUMMARY AND FUTURE DIRECTIONS Nanocasting is the most powerful method that is able to produce nanoporous carbons and metal oxides with ordered porous structures. The existing technical challenges include difficulties in finding a suitable inorganic precursor that can be converted directly to the desired phase with a continuous structure inside the silica template nanopores. At times, the target product requires very high temperatures to form the desired stoichiometry, and the silica template may not survive under such harsh conditions. This Account discussed some recent efforts in developing new synthetic strategies to overcome the technical barriers in current synthetic methods for nanoporous solids. Below is a brief summary of the recent advances in synthesizing nanoporous solids beyond traditional nanocasting methods.
Figure 8. TEM and HRTEM images of (a,b) nanoporous iron sulfide, (c,d) nanoporous nickel sulfide, and (e,f) nanoporous cobalt sulfide materials.
Selective Leaching−a Powerful Method to Create Porosity
Etching a condensed material in a controlled manner is an effective approach to produce highly porous materials as shown in the examples of nanoporous metals and hierarchical porous metal oxides. Considering the wide existence of multimetallic compounds, selective leaching could be a powerful tool to design mono- and bimetallic compounds with three-dimensionally interconnected pores, which are promising candidates for heterogeneous catalysis and energy storage and conversion. Similar opportunities also exist in hierarchical porous metal oxides that can be synthesized using selective leaching strategies.
nanoporous metal sulfides were analyzed using HRTEM, and the results (Figures 8b,d,f) showed clear crystal lattice fringes, indicating a highly crystalline nature for all three samples. Wide-angle PXRD results indicated that the pyrite phase was the dominate crystal structure in all three samples. The BET surface areas were 92, 86, and 77 m2 g−1 for FeS2, CoS2, and NiS2, respectively, which are close to those of nanocast metal oxides (∼100 m2 g−1). Energy-dispersive X-ray spectroscopy (EDS) results confirmed the chemical compositions of the assynthesized metal sulfides as Fe1.38S2, Co1.43S2, and Ni1.33S2, suggesting a sulfur deficit in the stoichiometry, a common phenomenon in metal sulfide reactions.60−62 Figure 9 shows the photocatalytic performances of nanoporous iron sulfide as well as its bulk counterpart. A suspension of catalyst and methylene blue mixture was exposed to visible light radiation, and the reaction rate was determined by UV−vis spectra as shown in Figure 9. The results demonstrated that nanoporous FeS2 exhibited a substantial improvement in methylene blue removal over bulk catalyst with an identical
Forming the Desired Phase Directly Inside Nanopores
Nanoporous Mo2C and W2C were synthesized using methane as the carbon source and reductant. The nanosized pores confined the carburization process to the scale of a few nanometers, which may reduce the temperature that is required to obtain pure-phase metal carbides. The strategy may be considered for the syntheses of other metal carbides such as NbC and TiC. Moreover, it is possible to extend this method further to metal phosphides and metal nitrides that have not yet been synthesized successfully. 1356
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(4) Antonelli, D. M.; Ying, J. Y. Synthesis of a stable hexagonally packed mesoporous niobium oxide molecular sieve through a novel ligand-assisted templating mechanism. Angew. Chem., Int. Ed. Engl. 1996, 35, 426−430. (5) Yang, P. D.; Zhao, D. Y.; Margolese, D. I.; Chmelka, B. F.; Stucky, G. D. Generalized syntheses of large-pore mesoporous metal oxides with semicrystalline frameworks. Nature 1998, 396, 152−155. (6) Ying, J. Y.; Mehnert, C. P.; Wong, M. S. Synthesis and applications of supramolecular-templated mesoporous materials. Angew. Chem., Int. Ed. 1999, 38, 56−77. (7) Soler-illia, G. J. D.; Sanchez, C.; Lebeau, B.; Patarin, J. Chemical strategies to design textured materials: From microporous and mesoporous oxides to nanonetworks and hierarchical structures. Chem. Rev. 2002, 102, 4093−4138. (8) Yang, H. F.; Zhao, D. Y. Synthesis of replica mesostructures by the nanocasting strategy. J. Mater. Chem. 2005, 15, 1217−1231. (9) Ren, Y.; Ma, Z.; Bruce, P. G. Ordered mesoporous metal oxides: synthesis and applications. Chem. Soc. Rev. 2012, 41, 4909−4927. (10) Lu, A. H.; Schuth, F. Nanocasting: A versatile strategy for creating nanostructured porous materials. Adv. Mater. 2006, 18, 1793− 1805. (11) Joo, S. H.; Choi, S. J.; Oh, I.; Kwak, J.; Liu, Z.; Terasaki, O.; Ryoo, R. Ordered nanoporous arrays of carbon supporting high dispersions of platinum nanoparticles. Nature 2001, 412, 169−172. (12) Li, G.; Zhang, D.; Yu, J. C. Ordered mesoporous BiVO4 through nanocasting: A superior visible light-driven photocatalyst. Chem. Mater. 2008, 20, 3983−3992. (13) Lu, A.-H.; Schueth, F. Nanocasting: A versatile strategy for creating nanostructured porous materials. Adv. Mater. 2006, 18, 1793− 1805. (14) Rumplecker, A.; Kleitz, F.; Salabas, E.-L.; Schueth, F. Hard templating pathways for the synthesis of nanostructured porous Co3O4. Chem. Mater. 2007, 19, 485−496. (15) Wang, Y. Q.; Yang, C. M.; Schmidt, W.; Spliethoff, B.; Bill, E.; Schuth, F. Weakly ferromagnetic ordered mesoporous CO3O4 synthesized by nanocasting from vinyl-functionalized cubic Ia3d mesoporous silica. Adv. Mater. 2005, 17, 53−56. (16) Tappan, B. C.; Steiner, S. A.; Luther, E. P. Nanoporous Metal Foams. Angew. Chem., Int. Ed. 2010, 49, 4544−4565. (17) Zhang, J. T.; Li, C. M. Nanoporous metals: fabrication strategies and advanced electrochemical applications in catalysis, sensing and energy systems. Chem. Soc. Rev. 2012, 41, 7016−7031. (18) Erlebacher, J.; Aziz, M. J.; Karma, A.; Dimitrov, N.; Sieradzki, K. Evolution of nanoporosity in dealloying. Nature 2001, 410, 450−453. (19) Zhang, Z. H.; Wang, Y.; Qi, Z.; Zhang, W. H.; Qin, J. Y.; Frenzel, J. Generalized Fabrication of Nanoporous Metals (Au, Pd, Pt, Ag, and Cu) through Chemical Dealloying. J. Phys. Chem. C 2009, 113, 12629−12636. (20) Jia, F. L.; Yu, C. F.; Deng, K. J.; Zhang, L. Z. Nanoporous metal (Cu, Ag, Au) films with high surface area: General fabrication and preliminary electrochemical performance. J. Phys. Chem. C 2007, 111, 8424−8431. (21) Pugh, D. V.; Dursun, A.; Corcoran, S. G. Formation of nanoporous platinum by selective dissolution of Cu from Cu0.75Pt0.25. J. Mater. Res. 2003, 18, 216−221. (22) Lu, Q.; Hutchings, G. S.; Yu, W. T.; Zhou, Y.; Forest, R. V.; Tao, R. Z.; Rosen, J.; Yonemoto, B. T.; Cao, Z. Y.; Zheng, H. M.; Xiao, J. Q.; Jiao, F.; Chen, J. G. G. Highly porous non-precious bimetallic electrocatalysts for efficient hydrogen evolution. Nat. Commun. 2015, 6, 6567. (23) Lu, Q.; Rosen, J.; Zhou, Y.; Hutchings, G. S.; Kimmel, Y. C.; Chen, J. G. G.; Jiao, F. A selective and efficient electrocatalyst for carbon dioxide reduction. Nat. Commun. 2014, 5, 3242. (24) Zhou, Y.; Lu, Q.; Zhuang, Z. B.; Hutchings, G. S.; Kattel, S.; Yan, Y. S.; Chen, J. G. G.; Xiao, J. Q.; Jiao, F. Oxygen Reduction at Very Low Overpotential on Nanoporous Ag Catalysts. Adv. Energy Mater. 2015, 5, 1500149. (25) Tian, B. Z.; Liu, X. Y.; Solovyov, L. A.; Liu, Z.; Yang, H. F.; Zhang, Z. D.; Xie, S. H.; Zhang, F. Q.; Tu, B.; Yu, C. Z.; Terasaki, O.;
In contrast to the formation process of nanoporous metal oxides through a dissolution-recrystallization mechanism, the synthesis of nanoporous metal sulfides was based on an “oxideto-sulfide” strategy. A nanoporous metal oxide was first formed using a traditional nanocasting procedure, followed by an additional chemical treatment step to convert oxide to sulfide. By doing so, undesired volume contraction was suppressed, resulting in a continuous three-dimensional porous structure. Despite this success, further efforts to optimize sulfidation conditions are required to prepare nanoporous metal sulfides with desired stoichiometric metal to sulfur ratios. Hunting for new synthetic methods beyond existing approaches is always important because the method holds the key to access nanoporous materials with unprecedented properties. Examples presented in this Account clearly showed a broad range of superior properties compared to their nonporous counterparts, suggesting their great potentials in heterogeneous catalysis and other applications. The discussions presented in this Account not only provide the community a brief overview of the recent progress in the synthesis of nanoporous metal-based solids but also strive to inspire new ideas and strategies for nanoporous material fabrication.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest. Biographies Wesley Luc studied at the University of California, San Diego and obtained his B.Sc. and M.Sc. degrees in Chemical Engineering in 2012 and 2013, respectively. He is now pursuing his Ph.D. degree in the Chemical and Biomolecular Engineering Department at the University of Delaware under the guidance of Dr. Feng Jiao. His current research is focused on the development of CO2 electroreduction catalysts and electrochemical process engineering for industrial applications. Feng Jiao obtained his B.Sc. in chemistry at Fudan University (2001) and his Ph.D. degree in Chemistry at the University of St. Andrews (Scotland, 2008) before moving to Lawrence Berkeley National Laboratory as a postdoctoral scholar. He spent two and half years at Berkeley developing solar fuel technology and joined in the Chemical and Biomolecular Engineering Department at the University of Delaware as an assistant professor in 2010. His current research interests include nanoporous materials, heterogeneous catalysis, and electrochemistry.
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ACKNOWLEDGMENTS The authors are thankful for financial support from the University of Delaware Energy Institute Innovative Energy Research Grants Program (IERGP) and the National Science Foundation CAREER Program (Award No. CBET-1350911).
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REFERENCES
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DOI: 10.1021/acs.accounts.6b00109 Acc. Chem. Res. 2016, 49, 1351−1358
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DOI: 10.1021/acs.accounts.6b00109 Acc. Chem. Res. 2016, 49, 1351−1358
