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Young Scientists
1
Nitrile-facilitated Proton Transfer for Enhanced Oxygen Reduction by
Hybrid Electrocatalysts
Abstract
Energy conservation and emission reduction, which attributes to the creation of a green and sustainable society, are important topics in the current social and economic development. Traditional tactics are often accompanied by heavy pollution, high energy consumption, and unclean production processes, while the late-model energy catalysis masters the key to achieving sustainable energy-efficient conversion. Low-temperature polymer electrolyte membrane fuel cells (PEMFCs) are considered to be a next-generation technology for the transportation sector, and the oxygen reduction reaction (ORR) is the chemical reaction occurring at a PEMFC cathode that fundamentally limits the overall performance of a PEMFC. While the multiple protons and electrons transfer steps, result in the deleterious reduced oxygen species (PROS). There is still plenty of room for improvement regarding the activity and selectivity of the artificial catalysts compared to ORR enzymes like laccase in nature. In order to enhance the activity and selectivity of the ORR electrocatalyst, a more thorough understanding and control of the proton and electron transfer steps involved in the ORR is necessary. Recently, hybrid bilayer membranes (HBMs), comprised of a self-assembled monolayer (SAM) covered by a lipid membrane, have been developed recently to regulate the performance of HBM-embedded electrocatalysts.1,2 However, no proton switch can be turned on in basic conditions and off in acidic conditions. We synthesized proton carriers bearing nitrile groups found in protonophores, and nature-inspired proton carriers can facilitate transmembrane proton delivery to an HBM-supported Cu ORR catalyst under alkaline conditions. Our stimuli-responsive proton regulators can turn on the activity of the ORR catalyst on-demand, thereby opening doors to investigate how proton transfer kinetics govern the performance of electrocatalysts for renewable energy conversion processes.
Figure 1. Cyano proton carrier regulates the activity of the ORR catalyst on demand.
Keywords: electrocatalysis; hybrid membrane; oxygen reduction reaction; energy conversion; PECT.
Reference
Keywords: electrocatalysis; hybrid membrane; oxygen reduction reaction; energy conversion; PECT.
References
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Gautam, R; Lee, Y. T.; Herman, G. L.; Moreno, C. M.; Tse, E. C. M.; Barile, C. J. Angew. Chem. Int. Ed., 2018, 57, 13480-13483.
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Zeng, T., Gautam, R. P., Barile, C. J., Li, Y., & Tse, E. C. M.; ACS Catalysis, 2020, 10(21): 13149-13155.
2
Enhanced Nitrite Electrovalorization to Ammonia by NiFe Layered Double Hydroxide
Abstract
The development of non-precious metal (NPM) electrocatalysts for efficient nitrite-toammonia upcycling is key to enabling a sustainable society. Here, an earth-abundant NiFe
layered double hydroxide (LDH) is prepared to electrochemically reduce nitrite with a Faradaic
efficiency as high as 85 %, an ammonia selectivity reaching 98 %, and an ammonia yield rate
up to 351 μmol h-1 mgcat-1, rivaling the performance metrics of state-of-the-art NPM catalysts.
NiFe LDH further displays excellent stability after 10 consecutive electrolysis runs with its
nanostructure unperturbed. By conducting electroreduction of nitrite in a range of solutions, the
electrolyte identity is found to play an important role in dictating the overall nitrite removal
activity. Through a comparative study with MgFe and NiAl inorganic solids, Ni and Fe are
demonstrated to boost nitrite valorization rate as well as ammonia selectivity and yield in a
synergistic manner. Taken together, these low-cost catalysts provide a promising strategy for
one-step conversion of nitrite into ammonia exclusively with implications in next-generation
wastewater treatment and green industrial commodity production.
Reference
1. Wang, W.; Tse, E. C. M.* European Journal of Inorganic Chemistry, 2022, Accepted
DOI:10.1002/ejic.202200291
3
Synthesis and Time-Resolved Spectroscopy of Catalysts for Solar-Driven H2 Generation
Dr. Wenchao WANG,
with Prof. ZX GUO and Prof. D.L. Phillips
The University of Hong Kong
E-mail: wenchao9@hku.hk
Abstract
Photocatalytic water-splitting for H2 production is an environmentally friendly and cost-effective way to zero-carbon energy supply. One of the key factors for efficient photocatalysis is to accelerate the separation and utilization of charge carriers. Due to the insufficient driving force, most single-component photocatalysts (e.g., TiO2, WO3, and CdS) show low H2 evolution activities due to the facile recombination of electron-hole pairs. Therefore, many efforts have focused on improving photoactivity by means of heterojunction / vacancy / doping against the intrinsic recombination. Graphitic carbon nitride (g-C3N4) as a metal-free material has been widely studied owing to its favorable band structure for visible-light response. 1,2 However, the key steps to affect photocatalytic H2 production of g-C3N4 are not very clear because of the ultrafast frequency of electron-hole recombination (usually in pico- / femto- second range).
With full consideration of the above, we resorted to an integrated strategy of synthesizing functional
g-C3N4 catalysts and monitoring charge carriers dynamics via time-resolved absorption spectroscopy:
1) In-situ proton fed interstitially phosphorus doped holey g-C3-xN4 to switch deep-to-shallow charge trapping (Figure 1a) and prolong the lifetime of active electrons to > 400 ps; 2) In2O3 nanocube induced near-field assistance system to provides catalytic “hot sites” for restraining electron-hole recombination and enhancing shallow trap states survival (Figure 1b).3 In summary, for g-C3N4 photocatalysis, it’s a promising strategy to improve photoactivity by promoting shallow charge trapping.
Figure 1. (a) Interstitially phosphorus doped holey g-C3-xN4; (b) femtosecond time-resolved absorption spectroscopic study of In2O3 nanocube modified g-C3N4 photocatalyst.
Reference
1. Lin, L.; Lin, Z.; Zhang, J.; Cai, X.; Lin, W.; Yu, Z.; Wang, X. Nat. Catal. 2020, 3, 649.
2. Ruan, Q.; Miao, T.; Wang, H.; Tang, J. J. Am. Chem. Soc. 2020, 142, 2795.
3. Wang, W.; Bai, X.; Ci, Q.; Du, L.; Ren, X.; Phillips, D. L. Adv. Funct. Mater. 2021, 31, 2103978.
