Electrochemical nitrogen reduction reaction (NRR) for ammonia synthesis might offer an alternative means to the capital- and carbon-intensive thermochemical process (Haber-Bosch) in a clean, sustainable, and decentralized way if the process is coupled to renewable electricity sources. One of the challenges in electrochemical ammonia synthesis is finding catalysts with a suitable activity for breaking N2 triple bonds at or near ambient conditions. Improving the design of electrocatalysts, electrolytes, and electrochemical cells is required to overcome the selectivity and activity barrier in electrochemical NRR. In-situ and operando surface-enhanced Raman spectroscopy (SERS) is a well-suited technique to probe electrochemical reactions at the solid-liquid (electrode/electrolyte) interface. Operando SERS allows for the detection of intermediate species even in low abundance and is used to provide insights into NRR mechanisms using hybrid plasmonic nanostructures (e.g., Au-Pd) by combining spectroscopy and electrochemistry. A potentiostat is used to apply potential on a SERS active substrate that is then monitored by changes in a spectrum. The spectroelectrochemical cell is developed to operando probe the trace of NH3 and possible intermediate species produced at the electrode/electrolyte interface. This work would aid in understanding the reaction mechanism and ultimately designing more efficient catalysts for electrochemical energy conversion systems.
This material is based upon work supported by the National Science Foundation under grant no. 1904351.
more »
« less
Photo-Electrochemical Ammonia Synthesis: Nanocatalyst Discovery, Reactor Design, and Advanced Spectroscopy
Ammonia holds great promise as a carbon-neutral liquid fuel for storing intermittent renewable energy sources and power generation due to its high energy density and hydrogen content. Photo-Electrochemical Ammonia Synthesis: Nanocatalyst Discovery, Reactor Design, and Advanced Spectroscopy covers the synthesis of novel hybrid plasmonic nanomaterials and their application in photo-electrochemical systems to convert low energy molecules to high value-added molecules and looks specifically at photo-electrochemical nitrogen reduction reaction (NRR) for ammonia synthesis as an attractive alternative to the long-lasting thermochemical process.
- Provides an integrated scientific framework, combining materials chemistry, photo-electrochemistry, and spectroscopy to overcome the challenges associated with renewable energy storage and transport
- Reviews materials chemistry for the synthesis of a range of heterogeneous (photo) electrocatalysts including plasmonic and hybrid plasmonic-semiconductor nanostructures for selective and efficient conversion of N2 to NH3
- Covers novel reactor design to study the redox processes in the photo-electrochemical energy conversion system and to benchmark nanocatalysts’ selectivity and activity toward NRR
- Discusses the use of advanced spectroscopic techniques to probe the reaction mechanism for ammonia synthesis
- Offers techno-economic analysis and presents performance targets for the scale-up and commercialization of electrochemical ammonia synthesis
This book is of value to researchers, advanced students, and industry professionals working in sustainable energy storage and conversion across the disciplines of Chemical Engineering, Mechanical Engineering, Materials Science and Engineering, Environmental Engineering, and related areas.
more »
« less
- Award ID(s):
- 1904351
- NSF-PAR ID:
- 10249377
- Date Published:
- Journal Name:
- CRC Press/ Taylor and Francis Group
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Motivated by the increasing demand for flexible and sustainable routes of ammonia (NH3) production, the electrochemical nitrogen (N2) and nitrate reduction reaction (NRR and NO3RR) have attracted intense research interest in the past few years1,2. Compared to the centralized Haber-Bosch process that operates at elevated temperature and pressure, the electrochemical pathway features mild operating conditions but high input energy density, allowing for distributed and on-site generation of NH3 with water as the proton source, thereby reducing the transportation and storage costs of NH3 and H23. Besides N2 which is highly abundant in the atmosphere, nitrate-N exists widely in agricultural and industrial wastewaters, and its presence has raised severe concerns due to its known impacts on the environment and human health4,5. In this regard, NO3RR provides a promising strategy of simultaneously removing the harmful nitrate-N and generating NH3 as a useful product from those wastewater streams. While research activities on both NRR and NO3RR are blooming with substantial progress in the field of electrocatalysis, some major challenges remain unnoticed or unresolved so far. Due to the wide existence of reactive N-containing species in laboratory environments, the source of NH3 in NRR measurements is sometimes elusive and requires rigorous examination by control experiments with costly 15N26,7. On the other hand, while the electro-reduction of nitrate is much more facile, additional costs arising from the enrichment and purification of nitrate in contaminated waste resources have challenged the practical feasibility of NO3RR both technically and economically2. In this talk, we will present our latest research progress as part of the solutions to these challenges in state-of-the-art NRR and NO3RR studies, from the perspective of reactor design. By taking advantage of the prior developments in 15N2 control experiments, here we suggest an improved 15N2 circulation system that is effective and affordable for NRR research, allowing for more accurate and economized quantitative assessment of NH3 origins, so that false positives and subtle catalytic activities can be identified more reliably. For NO3RR, we developed a compact reactor system for rapid and efficient electrochemical conversion of nitrate to NH3 from real nitrate-containing waste sources, accompanied by the concurrent separation and enrichment of the produced NH3 in a trapping solution to yield pure ammonium compounds. Our work highlights the importance of advanced reactor design in N-related electrochemistry research, which will facilitate the transformation of the current N-centric chemical industries towards a sustainable future.more » « less
-
more » « less
Abstract Clean and efficient energy storage and conversion via sustainable water and nitrogen reactions have attracted substantial attention to address the energy and environmental issues due to the overwhelming use of fossil fuels. These electrochemical reactions are crucial for desirable clean energy technologies, including advanced water electrolyzers, hydrogen fuel cells, and ammonia electrosynthesis and utilization. Their sluggish reaction kinetics lead to inefficient energy conversion. Innovative electrocatalysis, i.e., catalysis at the interface between the electrode and electrolyte to facilitate charge transfer and mass transport, plays a vital role in boosting energy conversion efficiency and providing sufficient performance and durability for these energy technologies. Herein, a comprehensive review on recent progress, achievements, and remaining challenges for these electrocatalysis processes related to water (i.e., oxygen evolution reaction, OER, and oxygen reduction reaction, ORR) and nitrogen (i.e., nitrogen reduction reaction, NRR, for ammonia synthesis and ammonia oxidation reaction, AOR, for energy utilization) is provided. Catalysts, electrolytes, and interfaces between the two within electrodes for these electrocatalysis processes are discussed. The primary emphasis is device performance of OER‐related proton exchange membrane (PEM) electrolyzers, ORR‐related PEM fuel cells, NRR‐driven ammonia electrosynthesis from water and nitrogen, and AOR‐related direct ammonia fuel cells.
-
Electro- and photocatalytic reduction of N 2 to NH 3 —the nitrogen reduction reaction (NRR)—is an environmentally- and energy-friendly alternative to the Haber-Bosch process for ammonia production. There is a great demand for the development of novel semiconductor-based electrocatalysts with high efficiency and stability for the direct conversion of inert substrates—including N 2 to ammonia—using visible light irradiation under ambient conditions. Herein we report electro-, and photocatalytic NRR with transition metal dichalcogenides (TMDCs), viz MoS 2 and WS 2 . Improved acid treatment of bulk TMDCs yields exfoliated TMDCs (exTMDCs) only a few layers thick with ∼10% S vacancies. Linear scan voltammograms on exMoS 2 and exWS 2 electrodes reveal significant NRR activity for exTMDC-modified electrodes, which is greatly enhanced by visible light illumination. Spectral measurements confirm ammonia as the main reaction product of electrocatalytic and photocatalytic NRR, and the absence of hydrazine byproduct. Femtosecond-resolved transient absorption studies provide direct evidence of interaction between photo-generated excitons/trions with N 2 adsorbed at S vacancies. DFT calculations corroborate N 2 binding to exMoS 2 at S-vacancies, with substantial π -backbonding to activate dinitrogen. Our findings suggest that chemically functionalized exTMDC materials could fulfill the need for highly-desired, inexpensive catalysts for the sustainable production of NH 3 using Sunlight under neutral pH conditions without appreciable competing production of H 2 .more » « less
-
Conventional lithium-ion batteries are unable to meet the increasing demands for high-energy storage systems, because of their limited theoretical capacity. 1 In recent years, intensive attention has been paid to enhancing battery energy storage capability to satisfy the increasing energy demand in modern society and reduce the average energy capacity cost. Among the candidates for next generation high energy storage systems, the lithium sulfur battery is especially attractive because of its high theoretical specific energy (around 2600 W h kg-1) and potential cost reduction. In addition, sulfur is a cost effective and environmentally friendly material due to its abundance and low-toxicity. 2 Despite all of these advantages, the practical application of lithium sulfur batteries to date has been hindered by a series of obstacles, including low active material loading, poor cycle life, and sluggish sulfur conversion kinetics. 3 Achieving high mass loading cathode in the traditional 2D planar thick electrode has been challenged. The high distorsion of the traditional planar thick electrodes for ion/electron transfer leads to the limited utilization of active materials and high resistance, which eventually results in restricted energy density and accelerated electrode failure. 4 Furthermore, of the electrolyte to pores in the cathode and utilization ratio of active materials. Catalysts such as MnO 2 and Co dopants were employed to accelerate the sulfur conversion reaction during the charge and discharge process. 5 However, catalysts based on transition metals suffer from poor electronic conductivity. Other catalysts such as transition metal dopants are also limited due to the increased process complexities. . In addition, the severe shuttle effects in Li-S batteries may lead to fast failures of the battery. Constructing a protection layer on the separator for limiting the transmission of soluble polysulfides is considered an effective way to eliminate the shuttle phenomenon. However, the soluble sulfides still can largely dissolve around the cathode side causing the sluggish reaction condition for sulfur conversion. 5 To mitigate the issues above, herein we demonstrate a novel sulfur electrode design strategy enabled by additive manufacturing and oxidative vapor deposition (oCVD). Specifically, the electrode is strategically designed into a hierarchal hollow structure via stereolithography technique to increase sulfur usage. The active material concentration loaded to the battery cathode is controlled precisely during 3D printing by adjusting the number of printed layers. Owing to its freedom in geometry and structure, the suggested design is expected to improve the Li ions and electron transport rate considerably, and hence, the battery power density. The printed cathode is sintered at 700 °C at N 2 atmosphere to achieve carbonization of the cathode during which intrinsic carbon defects (e.g., pentagon carbon) as catalytic defect sites are in-situ generated on the cathode. The intrinsic carbon defects equipped with adequate electronic conductivity. The sintered 3D cathode is then transferred to the oCVD chamber for depositing a thin PEDOT layer as a protection layer to restrict dissolutions of sulfur compounds in the cathode. Density functional theory calculation reveals the electronic state variance between the structures with and without defects, the structure with defects demonstrates the higher kinetic condition for sulfur conversion. To further identify the favorable reaction dynamic process, the in-situ XRD is used to characterize the transformation between soluble and insoluble polysulfides, which is the main barrier in the charge and discharge process of Li-S batteries. The results show the oCVD coated 3D printed sulfur cathode exhibits a much higher kinetic process for sulfur conversion, which benefits from the highly tailored hierarchal hollow structure and the defects engineering on the cathode. Further, the oCVD coated 3D printed sulfur cathode also demonstrates higher stability during long cycling enabled by the oCVD PEDOT protection layer, which is verified by an absorption energy calculation of polysulfides at PEDOT. Such modeling and analysis help to elucidate the fundamental mechanisms that govern cathode performance and degradation in Li-S batteries. The current study also provides design strategies for the sulfur cathode as well as selection approaches to novel battery systems. References: Bhargav, A., (2020). Lithium-Sulfur Batteries: Attaining the Critical Metrics. Joule 4 , 285-291. Chung, S.-H., (2018). Progress on the Critical Parameters for Lithium–Sulfur Batteries to be Practically Viable. Advanced Functional Materials 28 , 1801188. Peng, H.-J.,(2017). Review on High-Loading and High-Energy Lithium–Sulfur Batteries. Advanced Energy Materials 7 , 1700260. Chu, T., (2021). 3D printing‐enabled advanced electrode architecture design. Carbon Energy 3 , 424-439. Shi, Z., (2021). Defect Engineering for Expediting Li–S Chemistry: Strategies, Mechanisms, and Perspectives. Advanced Energy Materials 11 . Figure 1more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1201/9781003141808
