Emerging Nanocatalysts for Efficient Oxygen Reduction, Oxygen Evolution and Hydrogen Evolution

A special issue of Catalysts (ISSN 2073-4344). This special issue belongs to the section "Nanostructured Catalysts".

Deadline for manuscript submissions: closed (30 June 2021) | Viewed by 46380

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Guest Editor
School of Physics and Astronomy, Cardiff University, Cardiff, UK
Interests: quantum dot synthesis; quantum dot optoelectronics (PV, LED, photodetector, display and image sensors); electron microscopy (TEM) and dynamic charge transfer analysis
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Special Issue Information

Dear Colleagues,

The problem of global warming and global climate change cannot be ignored in any discussion regarding long-term environment policy—and the solution, as part of a comprehensive sustainable energy plan, is reducing or stopping greenhouse gas emissions which are generated through the release of naturally sequestered carbon via the human practice of burning fossil fuels. The ever-increasing detrimental effects of traditional fuels on the environment have stimulated extensive efforts worldwide to develop green and renewable energy technologies, including fuel cells, metal-air batteries and water-splitting systems. The fundamental electrochemical reaction mechanisms behind these renewable energy technologies are oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Indeed, the ORR is the heart of fuel cells, while the OER and HER are of paramount importance to metal-air batteries and electrochemical water-splitting systems. However, the large intrinsic overpotential associated with sluggish OER on anode and HER on the cathode make these electrochemical reactions inefficient. Thus, it is imperative to develop highly active catalysts to reduce the overpotential dramatically. So far, numerous promising nanocatalysts have been demonstrated, including i) multimetal oxide compound nanomaterials such as layered hydroxide, spinel and amorphous metal oxides; ii) metal-free nanocatalysts such as carbon nanotubes (CNTs), graphene, graphite, carbon nitride and 3D carbon architectures; iii) metallic transition–metal dichalcogenide (TMDC) nanocatalysts, where M represents a transition metal atom typically from group IVB to VIIB in the periodic table and X is a chalcogen atom such as S, Se, or Te; iv) Perovskite oxides (POs) such as ABO3±δ (where, A is alkaline or rare earth cations, B is first- row transition metal cations and δ is oxygen non-stoichiometry), Ruddlesden–Popper (An+ 1BnO3n + 1), Dion–Jacobson (AnBnO3n + 1), Aurivillius (Bi2An-1BnO3n + 3) homologous series, double- (A2BB’O6) and triple- (A2A’B2B’O9) layered POs, etc.

This Special Issue will focus on experimental and theoretical investigations into new nanocatalysts for the ORR, OER and HER, with a particular interest in the noble-metal-free or metal-free nanomaterials. Fundamental, applied studies, theoretical studies and advanced characterizations (structure, morphology, or interface charge transfer) are of interest. Additionally relevant are reports that detail new nanocatalysts for photoelectrolysis for water splitting, photocathodic protection and electrochemical organic degradation. The hope is to compile a set of manuscripts that inform the field of the state-of-the-art in electrochemical nanocatalysis.

Dr. Bo Hou
Guest Editor

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Keywords

  • oxygen reduction reaction (ORR)
  • oxygen evolution reaction (OER)
  • hydrogen evolution reaction (HER)
  • bifunctional electrocatalyst
  • metal-air batteries
  • water splitting
  • carbon materials
  • perovskite oxide
  • photocathodic protection
  • electrochemical organic degradation
  • electrochemical supercapacitor
  • fuel cells
  • solar fuels
  • photoelectrolysis
  • density functional theory
  • molecular dynamics
  • electron microscopy
  • electrochemical impedance spectroscopy

Published Papers (12 papers)

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Research

Jump to: Review

15 pages, 3067 KiB  
Article
Synthetic Mechanism Studies of Iron Selenides: An Emerging Class of Materials for Electrocatalysis
by Bo Hou, David Benito-Alifonso, Richard F. Webster, David Cherns, M. Carmen Galan and David J. Fermín
Catalysts 2021, 11(6), 681; https://doi.org/10.3390/catal11060681 - 27 May 2021
Cited by 7 | Viewed by 3482
Abstract
Solution-processed iron selenide nanocrystals (NCs) have recently attracted considerable attention in electrocatalysis water splitting. Nevertheless, a primary challenge in current iron-based NCs chemical synthesis is controlling phase purities between each chalcogen (monochalcogenide, dichalcogenides, and oxides), which requires a comprehensive understanding of the reaction [...] Read more.
Solution-processed iron selenide nanocrystals (NCs) have recently attracted considerable attention in electrocatalysis water splitting. Nevertheless, a primary challenge in current iron-based NCs chemical synthesis is controlling phase purities between each chalcogen (monochalcogenide, dichalcogenides, and oxides), which requires a comprehensive understanding of the reaction mechanisms at the early stages of nucleation. Herein, we investigate the fundamental steps in transforming molecular organoiron and organoselenium precursors to iron selenides NCs with the view of developing universal synthesis protocols for phase pure metal selenium and metal oxides NCs. The main intermediate species and volatile by-products are identified by high-resolution electron microscopy and Nuclear Magnetic Resonance (NMR) spectroscopy (1H, 13C, and 31P). Experimental evidence suggests that the phase determining factor is the coordinating reactivity difference between olefins (1-octadecene, oleylamine), tributylphosphine and trioctylphosphine associated with their corresponding Se bond cleavage. This work proposes organoselenium interconversion reaction mechanisms during iron selenides synthesis, offering a universal synthetic strategy for other electrocatalytically or photocatalytically active layered metal selenides materials. Full article
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11 pages, 30142 KiB  
Article
Net-Patterned Fluorine-Doped Tin Oxide to Accelerate the Electrochromic and Photocatalytic Interface Reactions
by Seock-Joon Jeong, Kue-Ho Kim and Hyo-Jin Ahn
Catalysts 2021, 11(2), 249; https://doi.org/10.3390/catal11020249 - 12 Feb 2021
Cited by 5 | Viewed by 2437
Abstract
In this study, the surface morphology of net-patterned fluorine-doped tin oxide (FTO) films was optimized with mesh sizes (60 mesh, 40 mesh, and 24 mesh) using the one-pot horizontal ultrasonic spray pyrolysis deposition (HUSPD) process. The 40M-FTO sample exhibited optimized electrical and optical [...] Read more.
In this study, the surface morphology of net-patterned fluorine-doped tin oxide (FTO) films was optimized with mesh sizes (60 mesh, 40 mesh, and 24 mesh) using the one-pot horizontal ultrasonic spray pyrolysis deposition (HUSPD) process. The 40M-FTO sample exhibited optimized electrical and optical properties due to the improved crystallinity and net-patterned surface morphology of FTO. The electrochromic (EC) electrodes fabricated with 40M-FTO showed superior EC performance, including transmittance modulation (ΔT, 58.7%), switching speeds (4.1 s for coloration and 5.9 s for bleaching), and coloration efficiency (CE, 52.4 cm2/C). These optimum values were attributed to the combined effect of the enhanced electrical properties from the improved crystallinity of the SnO2 and the high transmittance with a large surface area stemming from the optimization of the net-patterned FTO surface morphology. Moreover, the improved reaction sites with large surface area and enhanced electrical conductivity can facilitate the photocatalytic reaction. Accordingly, we suggest our novel strategy for use in creating promising transparent conducting electrodes that can be fabricated with net-patterned FTO to realize enhanced electrochromic and photocatalytic interface reactions. Full article
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10 pages, 2585 KiB  
Article
Hierarchically Ordinated Two-Dimensional MoS2 Nanosheets on Three-Dimensional Reduced Graphene Oxide Aerogels as Highly Active and Stable Catalysts for Hydrogen Evolution Reaction
by Hyeonggeun Choi, Suok Lee, Min-Cheol Kim, Yeonsu Park, A-Rang Jang, Wook Ahn, Jung Inn Sohn, Jong Bae Park, John Hong and Young-Woo Lee
Catalysts 2021, 11(2), 182; https://doi.org/10.3390/catal11020182 - 30 Jan 2021
Cited by 15 | Viewed by 3538
Abstract
Hydrogen gas (H2) is being intensively proposed as a next-generation clean energy owing to the depletion of fossil fuels. Electrochemical water splitting is one of the most promising processes for hydrogen production. Furthermore, many efforts focusing on electrochemical water splitting have [...] Read more.
Hydrogen gas (H2) is being intensively proposed as a next-generation clean energy owing to the depletion of fossil fuels. Electrochemical water splitting is one of the most promising processes for hydrogen production. Furthermore, many efforts focusing on electrochemical water splitting have been made to develop low-cost, electrochemically active, and stable catalysts for efficient hydrogen production. MoS2 has emerged as an attractive material for developing catalysts for the hydrogen evolution reaction (HER). Hence, in this study, we design hierarchically ordinated two-dimensional (2D) MoS2 nanosheets on three-dimensional (3D) reduced graphene oxide (rGO) (H-2D/3D-MoS2-rGO) aerogel structures as a new class of electrocatalysts for the HER. We use the one-pot hydrothermal synthesis route for developing high-performance electroactive materials for the HER. The as-prepared H-2D/3D-MoS2-rGO contains a unique 3D hierarchical structure providing large surface areas owing to the 3D porous networks of rGO and more active sites owing to the many edge sites in the MoS2 nanosheets. In addition, the H-2D/3D-MoS2-rGO structure exhibits remarkable electrochemical properties during the HER. It shows a lower overpotential than pure MoS2 and excellent electrochemical stability owing to the large number of active sites (highly exposed edge sites) and high electrical conductivity from the rGO structure. Full article
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9 pages, 1498 KiB  
Article
Enhanced Hydrogen Evolution Reaction in Surface Functionalized MoS2 Monolayers
by Sangyeon Pak, Jungmoon Lim, John Hong and SeungNam Cha
Catalysts 2021, 11(1), 70; https://doi.org/10.3390/catal11010070 - 6 Jan 2021
Cited by 19 | Viewed by 3727
Abstract
Monolayered, semiconducting MoS2 and their transition metal dichalcogenides (TMDCs) families are promising and low-cost materials for hydrogen generation through electrolytes (HER, hydrogen evolution reaction) due to their high activities and electrochemical stability during the reaction. However, there is still a lack of [...] Read more.
Monolayered, semiconducting MoS2 and their transition metal dichalcogenides (TMDCs) families are promising and low-cost materials for hydrogen generation through electrolytes (HER, hydrogen evolution reaction) due to their high activities and electrochemical stability during the reaction. However, there is still a lack of understanding in identifying the underlying mechanism responsible for improving the electrocatalytic properties of theses monolayers. In this work, we investigated the significance of controlling carrier densities in a MoS2 monolayer and in turn the corresponding electrocatalytic behaviors in relation to the energy band structure of MoS2. Surface functionalization was employed to achieve p-doping and n-doping in the MoS2 monolayer that led to MoS2 electrochemical devices with different catalytic performances. Specifically, the electron-rich MoS2 surface showed lower overpotential and Tafel slope compared to the MoS2 with surface functional groups that contributed to p-doping. We attributed such enhancement to the increase in the carrier density and the corresponding Fermi level that accelerated HER and charge transfer kinetics. These findings are of high importance in designing electrocatalysts based on two-dimensional TMDCs. Full article
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18 pages, 4583 KiB  
Communication
Reducing the Photodegradation of Perovskite Quantum Dots to Enhance Photocatalysis in CO2 Reduction
by Hanleem Lee, Meeree Kim and Hyoyoung Lee
Catalysts 2021, 11(1), 61; https://doi.org/10.3390/catal11010061 - 5 Jan 2021
Cited by 7 | Viewed by 3665
Abstract
Solution-processed perovskite quantum dots (QDs) have been intensively researched as next-generation photocatalysts owing to their outstanding optical properties. Even though the intrinsic physical properties of perovskite QDs have been significantly improved, the chemical stability of these materials remains questionable. Their low long-term chemical [...] Read more.
Solution-processed perovskite quantum dots (QDs) have been intensively researched as next-generation photocatalysts owing to their outstanding optical properties. Even though the intrinsic physical properties of perovskite QDs have been significantly improved, the chemical stability of these materials remains questionable. Their low long-term chemical stability limits their commercial applicability in photocatalysis. In this study, we investigated the photodegradation mechanisms of perovskite QDs and their hybrids via photoluminescence (PL) by varying the excitation power and the ultraviolet (UV) exposure power. Defects in perovskite QDs and the interface between the perovskite QD and the co-catalyst influence the photo-stability of perovskite QDs. Consequently, we designed a stable perovskite QD film via an in-situ cross-linking reaction with amine-based silane materials. The surface ligand comprising 2,6-bis(N-pyrazolyl)pyridine nickel(II) bromide (Ni(ppy)) and 5-hexynoic acid improved the interface between the Ni co-catalyst and the perovskite QD. Then, ultrathin SiO2 was fabricated using 3-aminopropyltriethoxy silane (APTES) to harness the strong surface binding energy of the amine functional group of APTES with the perovskite QDs. The Ni co-catalyst content was further increased through Ni doping during purification using a short surface ligand (3-butynoic acid). As a result, stable perovskite QDs with rapid charge separation were successfully fabricated. Time-correlated single photon counting (TCSPC) PL study demonstrated that the modified perovskite QD film exhibited slow photodegradation owing to defect passivation and the enhanced interface between the Ni co-catalyst and the perovskite QD. This interface impeded the generation of hot carriers, which are a critical factor in photodegradation. Finally, a stable red perovskite QD was synthesized by applying the same strategy and the mixture between red and green QD/Ni(ppy)/SiO2 displayed an CO2 reduction capacity for CO (0.56 µmol/(g∙h)). Full article
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9 pages, 24515 KiB  
Article
Redox-Mediated Polymer Catalyst for Lithium-Air Batteries with High Round-Trip Efficiency
by Min-Cheol Kim, Jung Hyun Song, Young-Woo Lee and Jung Inn Sohn
Catalysts 2020, 10(12), 1479; https://doi.org/10.3390/catal10121479 - 17 Dec 2020
Cited by 2 | Viewed by 2724
Abstract
Lithium-air batteries (LABs) continue to receive attention as a promising power source because they possess a high theoretical energy density of 3436 Wh L−1. However, the remaining Li2O2 resulting from the irreversible decomposition of Li2O2 [...] Read more.
Lithium-air batteries (LABs) continue to receive attention as a promising power source because they possess a high theoretical energy density of 3436 Wh L−1. However, the remaining Li2O2 resulting from the irreversible decomposition of Li2O2 during the charge process is one of the key challenges so as to address the deterioration of the cycling performance of LABs. In this study, we propose and report a redox-mediated polymer catalyst (RPC) as a cathode catalyst being composed of LiI and poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with multi-wall carbon nanotubes (MWCNTs) as the cathode material. In the RPC, iodine molecules are chemically combined with the PVDF-HFP chain. The as-prepared RPC exhibits increased cycling performance by 194% and decreased overpotential by 21.1% at 0.1 mA cm−2 compared to the sample without LiI molecules. Furthermore, these results suggest that the RPC consisting of a polymer chain and redox mediators will be extensively utilized as highly efficient catalysts of LABs. Full article
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14 pages, 4217 KiB  
Article
Accelerating the Oxygen Reduction Reaction and Oxygen Evolution Reaction Activities of N and P Co-Doped Porous Activated Carbon for Li-O2 Batteries
by Hyun-Gi Jo and Hyo-Jin Ahn
Catalysts 2020, 10(11), 1316; https://doi.org/10.3390/catal10111316 - 13 Nov 2020
Cited by 18 | Viewed by 2883
Abstract
Rechargeable lithium–oxygen (Li-O2) batteries represent state-of-the-art electrochemical energy storage devices that provide high energy densities. However, their commercialization is challenging owing to their low charging/discharging efficiencies, short battery lives, high overpotentials, and high cathode manufacturing costs. In this study, we prepared [...] Read more.
Rechargeable lithium–oxygen (Li-O2) batteries represent state-of-the-art electrochemical energy storage devices that provide high energy densities. However, their commercialization is challenging owing to their low charging/discharging efficiencies, short battery lives, high overpotentials, and high cathode manufacturing costs. In this study, we prepared a metal-free, N,P co-doped, porous activated carbon (N,P-PAC) electrode via KOH activation and P doping for application as a Li-O2 battery cathode. When used in a rechargeable Li-O2 battery, the N,P-PAC cathode showed a high specific discharge capacity (3724 mA h g−1 at 100 mA g−1), an excellent cycling stability (25 cycles with a limit capacity of 1000 mA h g−1), and a low charge/discharge voltage gap (1.22 V at 1000 mA h g−1). The N,P-PAC electrode showed a low overpotential (EOER-ORR) of 1.54 V. The excellent electrochemical performance of the N,P-PAC electrode can mainly be attributed to its large active area and oxygen-containing functional groups generated via KOH activation and P-doping processes. Therefore, the N,P-PAC prepared in this study was found to be a promising eco-friendly and sustainable metal-free cathode material for Li-O2 batteries. Full article
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8 pages, 1862 KiB  
Article
Simple and Facile Fabrication of Anion-Vacancy-Induced MoO3−X Catalysts for Enhanced Hydrogen Evolution Activity
by Seunghwan Jo, Young-Woo Lee, John Hong and Jung Inn Sohn
Catalysts 2020, 10(10), 1180; https://doi.org/10.3390/catal10101180 - 14 Oct 2020
Cited by 13 | Viewed by 2499
Abstract
Advanced catalysts for clean hydrogen generation and storage offer an attractive possibility for developing a sustainable and ecofriendly future energy system. Transition metal oxides (TMO) are appealing candidates to be largely considered as electrode catalysts. However, for practical applications, there are still challenges—the [...] Read more.
Advanced catalysts for clean hydrogen generation and storage offer an attractive possibility for developing a sustainable and ecofriendly future energy system. Transition metal oxides (TMO) are appealing candidates to be largely considered as electrode catalysts. However, for practical applications, there are still challenges—the intrinsic catalytic properties of TMOs should be further improved and TMOs should be synthesized by practical routes for cost-effective and scalable production of catalysts. Therefore, finding promising ways to fabricate highly active TMOs with outstanding electrochemical hydrogen evolution performance is required. Here, we present a direct and facile synthetic approach to successfully provide highly efficient MoO3−X catalysts with electrochemically active oxygen vacancies through a one-step thermal activation process on a Mo metal mesh. Variations in the oxidation states of molybdenum oxides can significantly increase the active sites of the catalysts and improve the electrochemical activity, making these oxide compounds suitable for hydrogen evolution reaction (HER). Compared to the bare Mo mesh and fully oxidized Mo (MoO3) electrodes, the fabricated MoO3−X electrode exhibits better electrochemical performance in terms of overpotentials and Tafel slope, as well as the electrochemical 1000 cycling stability, confirming the improved HER performance of MoO3−X. This provides new insight into the simple procedure suitable for the large-production supply. Full article
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12 pages, 2653 KiB  
Article
Thermal Profiles of Carbon Fiber Based Anisotropic Thin-Films: An Emerging Heat Management Solution for High-Current Flow Electrocatalysis and Electrochemical Applications
by Sang-Hwi Lim and Han-Ki Kim
Catalysts 2020, 10(10), 1172; https://doi.org/10.3390/catal10101172 - 12 Oct 2020
Cited by 3 | Viewed by 2108
Abstract
Carbon fiber has been extensively used in the photocatalysis, electrocatalysis and energy storage fields as supporting platform and conductive media. However, less attention has been paid with regards to its function in phonon transport and thermal management. We have investigated the effect of [...] Read more.
Carbon fiber has been extensively used in the photocatalysis, electrocatalysis and energy storage fields as supporting platform and conductive media. However, less attention has been paid with regards to its function in phonon transport and thermal management. We have investigated the effect of current flow direction on the heat management performance of carbon fiber based thin film heaters (CFTFHs) with anisotropic percolation network of carbon fibers (CFs). The anisotropic percolation network of carbon fibers (CFs) formed by roll-to-roll spray coating leads to the anisotropic electrical properties of CFs. As a result, CFs based thin films (CFTFs) have lower sheet resistance when measured parallel to the CFs alignment, compared to when they are aligned perpendicular. Because connectivity and current flow in CFs are critically dependent on the direction alignment of CFs, the saturation temperature (106.4 °C) of CFTFH with parallel aligned carbon fiber is higher than that (117.3 °C) of CFTFH with perpendicular alignment. Therefore, current flow in the same direction as the alignment of CFs is very important to achieve high-performance. Moreover, our study on thermal profile of anisotropic CFTFs under high current flows illustrates that carbon fiber thin films have great potential in thermal management solution for electrocatalytic and electrochemical energy storage applications. Full article
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14 pages, 3514 KiB  
Article
Synthesis of Lanthanide-Functionalized Carbon Quantum Dots for Chemical Sensing and Photocatalytic Application
by Fu-Ran Zou, Sai-Nan Wang, Fang-Fang Wang, Dan Liu and Ying Li
Catalysts 2020, 10(8), 833; https://doi.org/10.3390/catal10080833 - 24 Jul 2020
Cited by 8 | Viewed by 3514
Abstract
Tunable photoluminescent-functionalized carbon quantum dots CQDs@Ln (TFA)3 (Ln = Eu, Tb; TFA: trifluoroacetylacetone) were designed and synthesized by introducing lanthanide complexes into the modified CQDs surface through the carboxyl group. The as-prepared CQDs@Ln (TFA)3 emit strong blue–green light with the peak [...] Read more.
Tunable photoluminescent-functionalized carbon quantum dots CQDs@Ln (TFA)3 (Ln = Eu, Tb; TFA: trifluoroacetylacetone) were designed and synthesized by introducing lanthanide complexes into the modified CQDs surface through the carboxyl group. The as-prepared CQDs@Ln (TFA)3 emit strong blue–green light with the peak at 435 nm and simultaneously show the characteristic emission of Ln3+ under irradiation of 365 nm light in aqueous solution. Moreover, these functionalized CQDs exhibit excellent photoluminescence properties. In addition, a white luminescent solution CQDs@Eu/Tb (TFA)3 was obtained by adjusting the ratio of Eu3+/Tb3+ and the excitation wavelengths. Moreover, CQDs@Tb (TFA)3 can be utilized as a fluorescent probe for the sensitive and selective detection of MnO4 without interference from other ions in aqueous solution. These results provide the meaningful data for the multicomponent assembly and the photoluminescent-functionalized materials based on the modified CQDs and lanthanide, which can be expected to have potential application in photocatalytic or sensors. Full article
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Review

Jump to: Research

20 pages, 3548 KiB  
Review
Molecular Dynamics and Machine Learning in Catalysts
by Wenxiang Liu, Yang Zhu, Yongqiang Wu, Cen Chen, Yang Hong, Yanan Yue, Jingchao Zhang and Bo Hou
Catalysts 2021, 11(9), 1129; https://doi.org/10.3390/catal11091129 - 19 Sep 2021
Cited by 16 | Viewed by 8125
Abstract
Given the importance of catalysts in the chemical industry, they have been extensively investigated by experimental and numerical methods. With the development of computational algorithms and computer hardware, large-scale simulations have enabled influential studies with more atomic details reflecting microscopic mechanisms. This review [...] Read more.
Given the importance of catalysts in the chemical industry, they have been extensively investigated by experimental and numerical methods. With the development of computational algorithms and computer hardware, large-scale simulations have enabled influential studies with more atomic details reflecting microscopic mechanisms. This review provides a comprehensive summary of recent developments in molecular dynamics, including ab initio molecular dynamics and reaction force-field molecular dynamics. Recent research on both approaches to catalyst calculations is reviewed, including growth, dehydrogenation, hydrogenation, oxidation reactions, bias, and recombination of carbon materials that can guide catalyst calculations. Machine learning has attracted increasing interest in recent years, and its combination with the field of catalysts has inspired promising development approaches. Its applications in machine learning potential, catalyst design, performance prediction, structure optimization, and classification have been summarized in detail. This review hopes to shed light and perspective on ML approaches in catalysts. Full article
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24 pages, 5054 KiB  
Review
Emerging Energy Harvesting Technology for Electro/Photo-Catalytic Water Splitting Application
by Jianfei Tang, Tianle Liu, Sijia Miao and Yuljae Cho
Catalysts 2021, 11(1), 142; https://doi.org/10.3390/catal11010142 - 19 Jan 2021
Cited by 26 | Viewed by 6078
Abstract
In recent years, we have experienced extreme climate changes due to the global warming, continuously impacting and changing our daily lives. To build a sustainable environment and society, various energy technologies have been developed and introduced. Among them, energy harvesting, converting ambient environmental [...] Read more.
In recent years, we have experienced extreme climate changes due to the global warming, continuously impacting and changing our daily lives. To build a sustainable environment and society, various energy technologies have been developed and introduced. Among them, energy harvesting, converting ambient environmental energy into electrical energy, has emerged as one of the promising technologies for a variety of energy applications. In particular, a photo (electro) catalytic water splitting system, coupled with emerging energy harvesting technology, has demonstrated high device performance, demonstrating its great social impact for the development of the new water splitting system. In this review article, we introduce and discuss in detail the emerging energy-harvesting technology for photo (electro) catalytic water splitting applications. The article includes fundamentals of photocatalytic and electrocatalytic water splitting and water splitting applications coupled with the emerging energy-harvesting technologies using piezoelectric, piezo-phototronic, pyroelectric, triboelectric, and photovoltaic effects. We comprehensively deal with different mechanisms in water splitting processes with respect to the energy harvesting processes and their effect on the water splitting systems. Lastly, new opportunities in energy harvesting-assisted water splitting are introduced together with future research directions that need to be investigated for further development of new types of water splitting systems. Full article
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