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2 pages, 167 KiB

Open AccessEditorial

Electrocatalysts for Oxygen/Hydrogen-Involved Reactions

by Jingqi Guan and Yin Wang

Molecules 2022, 27(9), 2628; https://doi.org/10.3390/molecules27092628 - 19 Apr 2022

Cited by 1 | Viewed by 1519

Abstract

Oxygen/hydrogen-involved reactions are key reactions in many energy-related technologies, such as electrolytic water, electrocatalytic carbon dioxide reduction, electrochemical ammonia synthesis, rechargeable metal–air batteries, and renewable fuel cells [...] Full article

(This article belongs to the Special Issue Electrocatalysts for Oxygen/Hydrogen-Involved Reactions)

Research

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10 pages, 3225 KiB

Open AccessArticle

Theoretical Investigation on the Hydrogen Evolution, Oxygen Evolution, and Oxygen Reduction Reactions Performances of Two-Dimensional Metal-Organic Frameworks Fe₃(C₂X)₁₂ (X = NH, O, S)

by Xiaohang Yang, Zhen Feng and Zhanyong Guo

Molecules 2022, 27(5), 1528; https://doi.org/10.3390/molecules27051528 - 24 Feb 2022

Cited by 11 | Viewed by 2984

Abstract

Two-dimensional metal-organic frameworks (2D MOFs) inherently consisting of metal entities and ligands are promising single-atom catalysts (SACs) for electrocatalytic chemical reactions. Three 2D Fe-MOFs with NH, O, and S ligands were designed using density functional theory calculations, and their feasibility as SACs for [...] Read more.

Two-dimensional metal-organic frameworks (2D MOFs) inherently consisting of metal entities and ligands are promising single-atom catalysts (SACs) for electrocatalytic chemical reactions. Three 2D Fe-MOFs with NH, O, and S ligands were designed using density functional theory calculations, and their feasibility as SACs for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) was investigated. The NH, O, and S ligands can be used to control electronic structures and catalysis performance in 2D Fe-MOF monolayers by tuning charge redistribution. The results confirm the Sabatier principle, which states that an ideal catalyst should provide reasonable adsorption energies for all reaction species. The 2D Fe-MOF nanomaterials may render highly-efficient HER, OER, and ORR by tuning the ligands. Therefore, we believe that this study will serve as a guide for developing of 2D MOF-based SACs for water splitting, fuel cells, and metal-air batteries. Full article

(This article belongs to the Special Issue Electrocatalysts for Oxygen/Hydrogen-Involved Reactions)

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11 pages, 3539 KiB

Open AccessArticle

Sm_0.5Sr_0.5Co_1−xNi_xO_3−δ—A Novel Bifunctional Electrocatalyst for Oxygen Reduction/Evolution Reactions

by Xingmei Liu, Yuwei Wang, Liquan Fan, Weichao Zhang, Weiyan Cao, Xianxin Han, Xijun Liu and Hongge Jia

Molecules 2022, 27(4), 1263; https://doi.org/10.3390/molecules27041263 - 14 Feb 2022

Cited by 3 | Viewed by 1579

Abstract

The development of non-precious metal catalysts with excellent bifunctional activities is significant for air–metal batteries. ABO₃-type perovskite oxides can improve their catalytic activity and electronic conductivity by doping transition metal elements at B sites. Here, we develop a novel Sm_0.5 [...] Read more.

The development of non-precious metal catalysts with excellent bifunctional activities is significant for air–metal batteries. ABO₃-type perovskite oxides can improve their catalytic activity and electronic conductivity by doping transition metal elements at B sites. Here, we develop a novel Sm_0.5Sr_0.5Co_1−xNi_xO_3−δ (SSCN) nanofiber-structured electrocatalyst. In 0.1 M KOH electrolyte solution, Sm_0.5Sr_0.5Co_0.8Ni_0.2O_3−δ (SSCN82) with the optimal Co: Ni molar ratio exhibits good electrocatalytic activity for OER/ORR, affording a low onset potential of 1.39 V, a slight Tafel slope of 123.8 mV dec⁻¹, and a current density of 6.01 mA cm⁻² at 1.8 V, and the ORR reaction process was four-electron reaction pathway. Combining the morphological characteristic of SSCN nanofibers with the synergistic effect of cobalt and nickel with a suitable molar ratio is beneficial to improving the catalytic activity of SSCN perovskite oxides. SSCN82 exhibits good bi-functional catalytic performance and electrochemical double-layer capacitance. Full article

(This article belongs to the Special Issue Electrocatalysts for Oxygen/Hydrogen-Involved Reactions)

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16 pages, 33316 KiB

Open AccessArticle

Nickel-Based Metal-Organic Frameworks as Electrocatalysts for the Oxygen Evolution Reaction (OER)

by Linda Sondermann, Wulv Jiang, Meital Shviro, Alex Spieß, Dennis Woschko, Lars Rademacher and Christoph Janiak

Molecules 2022, 27(4), 1241; https://doi.org/10.3390/molecules27041241 - 12 Feb 2022

Cited by 42 | Viewed by 7610

Abstract

The exploration of earth-abundant electrocatalysts with high performance for the oxygen evolution reaction (OER) is eminently desirable and remains a significant challenge. The composite of the metal-organic framework (MOF) Ni₁₀Co-BTC (BTC = 1,3,5-benzenetricarboxylate) and the highly conductive carbon material ketjenblack (KB) [...] Read more.

The exploration of earth-abundant electrocatalysts with high performance for the oxygen evolution reaction (OER) is eminently desirable and remains a significant challenge. The composite of the metal-organic framework (MOF) Ni₁₀Co-BTC (BTC = 1,3,5-benzenetricarboxylate) and the highly conductive carbon material ketjenblack (KB) could be easily obtained from the MOF synthesis in the presence of KB in a one-step solvothermal reaction. The composite and the pristine MOF perform better than commercially available Ni/NiO nanoparticles under the same conditions for the OER. Activation of the nickel-cobalt clusters from the MOF can be seen under the applied anodic potential, which steadily boosts the OER performance. Ni₁₀Co-BTC and Ni₁₀Co-BTC/KB are used as sacrificial agents and undergo structural changes during electrochemical measurements, the stabilized materials show good OER performances. Full article

(This article belongs to the Special Issue Electrocatalysts for Oxygen/Hydrogen-Involved Reactions)

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14 pages, 3276 KiB

Open AccessArticle

The Facile Deposition of Pt Nanoparticles on Reduced Graphite Oxide in Tunable Aryl Alkyl Ionic Liquids for ORR Catalysts

by Dennis Woitassek, Swantje Lerch, Wulv Jiang, Meital Shviro, Stefan Roitsch, Thomas Strassner and Christoph Janiak

Molecules 2022, 27(3), 1018; https://doi.org/10.3390/molecules27031018 - 2 Feb 2022

Cited by 6 | Viewed by 2705

Abstract

In this study, we present the facile formation of platinum nanoparticles (Pt-NPs) on reduced graphite oxide (rGO) (Pt-NP@rGO) by microwave-induced heating of the organometallic precursor ((MeCp)PtMe₃ in different tunable aryl alkyl ionic liquids (TAAIL). In the absence of rGO, transmission electron microscopy [...] Read more.

In this study, we present the facile formation of platinum nanoparticles (Pt-NPs) on reduced graphite oxide (rGO) (Pt-NP@rGO) by microwave-induced heating of the organometallic precursor ((MeCp)PtMe₃ in different tunable aryl alkyl ionic liquids (TAAIL). In the absence of rGO, transmission electron microscopy (TEM) reveals the formation of dense aggregates of Pt-NPs, with primary particle sizes of 2 to 6 nm. In contrast, in the Pt-NP@rGO samples, Pt-NPs are homogeneously distributed on the rGO, without any aggregation. Pt-NP@rGO samples are used as electrode materials for oxygen reduction reaction (ORR), which was assessed by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The electrochemical surface area (ECSA) and mass-specific activity (MA) increase up to twofold, compared with standard Pt/C 60%, making Pt-NP@rGO a competitive material for ORR. Full article

(This article belongs to the Special Issue Electrocatalysts for Oxygen/Hydrogen-Involved Reactions)

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10 pages, 2996 KiB

Open AccessArticle

PtNi Alloy Coated in Porous Nitrogen-Doped Carbon as Highly Efficient Catalysts for Hydrogen Evolution Reactions

by Xuyan Song, Yunlu He, Bo Wang, Sanwen Peng, Lin Tong, Qiang Liu, Jun Yu and Haolin Tang

Molecules 2022, 27(2), 499; https://doi.org/10.3390/molecules27020499 - 14 Jan 2022

Cited by 6 | Viewed by 2501

Abstract

The development of low platinum loading hydrogen evolution reaction (HER) catalysts with high activity and stability is of great significance to the practical application of hydrogen energy. This paper reports a simple method to synthesize a highly efficient HER catalyst through coating a [...] Read more.

The development of low platinum loading hydrogen evolution reaction (HER) catalysts with high activity and stability is of great significance to the practical application of hydrogen energy. This paper reports a simple method to synthesize a highly efficient HER catalyst through coating a highly dispersed PtNi alloy on porous nitrogen-doped carbon (MNC) derived from the zeolite imidazolate skeleton. The catalyst is characterized and analyzed by physical characterization methods, such as XRD, SEM, TEM, BET, XPS, and LSV, EIS, it, v-t, etc. The optimized sample exhibits an overpotential of only 26 mV at a current density of 10 mA cm⁻², outperforming commercial 20 wt% Pt/C (33 mV). The synthesized catalyst shows a relatively fast HER kinetics as evidenced by the small Tafel slope of 21.5 mV dec⁻¹ due to the small charge transfer resistance, the alloying effect between Pt and Ni, and the interaction between PtNi alloy and carrier. Full article

(This article belongs to the Special Issue Electrocatalysts for Oxygen/Hydrogen-Involved Reactions)

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14 pages, 2437 KiB

Open AccessArticle

Non-PGM Electrocatalysts for PEM Fuel Cells: A DFT Study on the Effects of Fluorination of FeN_x-Doped and N-Doped Carbon Catalysts

by Mohamed Cherif, Jean-Pol Dodelet, Gaixia Zhang, Vassili P. Glibin, Shuhui Sun and François Vidal

Molecules 2021, 26(23), 7370; https://doi.org/10.3390/molecules26237370 - 4 Dec 2021

Cited by 8 | Viewed by 2410

Abstract

Fluorination is considered as a means of reducing the degradation of Fe/N/C, a highly active FeN_x-doped disorganized carbon catalyst for the oxygen reduction reaction (ORR) in PEM fuel cells. Our recent experiments have, however, revealed that fluorination poisons the FeN_x [...] Read more.

Fluorination is considered as a means of reducing the degradation of Fe/N/C, a highly active FeN_x-doped disorganized carbon catalyst for the oxygen reduction reaction (ORR) in PEM fuel cells. Our recent experiments have, however, revealed that fluorination poisons the FeN_x moiety of the Fe/N/C catalytic site, considerably reducing the activity of the resulting catalyst to that of carbon only doped with nitrogen. Using the density functional theory (DFT), we clarify in this work the mechanisms by which fluorine interacts with the catalyst. We studied 10 possible FeN_x site configurations as well as 2 metal-free sites in the absence or presence of fluorine molecules and atoms. When the FeN_x moiety is located on a single graphene layer accessible on both sides, we found that fluorine binds strongly to Fe but that two F atoms, one on each side of the FeN_x plane, are necessary to completely inhibit the catalytic activity of the FeN_x sites. When considering the more realistic model of a stack of graphene layers, only one F atom is needed to poison the FeN_x moiety on the top layer since ORR hardly takes place between carbon layers. We also found that metal-free catalytic N-sites are immune to poisoning by fluorination, in accordance with our experiments. Finally, we explain how most of the catalytic activity can be recovered by heating to 900 °C after fluorination. This research helps to clarify the role of metallic sites compared to non-metallic ones upon the fluorination of FeN_x-doped disorganized carbon catalysts. Full article

(This article belongs to the Special Issue Electrocatalysts for Oxygen/Hydrogen-Involved Reactions)

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11 pages, 2037 KiB

Open AccessArticle

A Nanosheet-Assembled SnO₂-Integrated Anode

by Xiaoli Wang, Xinyu Zhao and Yin Wang

Molecules 2021, 26(20), 6108; https://doi.org/10.3390/molecules26206108 - 10 Oct 2021

Cited by 3 | Viewed by 1856

Abstract

There is an ever-increasing trend toward bendable and high-energy-density electrochemical storage devices with high strength to fulfil the rapid development of flexible electronics, but they remain a great challenge to be realised by the traditional slurry-casting fabrication processes. To overcome these issues, herein, [...] Read more.

There is an ever-increasing trend toward bendable and high-energy-density electrochemical storage devices with high strength to fulfil the rapid development of flexible electronics, but they remain a great challenge to be realised by the traditional slurry-casting fabrication processes. To overcome these issues, herein, a facile strategy was proposed to design integrating an electrode with flexible, high capacity, and high tensile strength nanosheets with interconnected copper micro-fibre as a collector, loaded with a novel hierarchical SnO₂ nanoarchitecture, which were assembled into core–shell architecture, with a 1D micro-fibre core and 2D nanosheets shell. When applied as anode materials for LIBs, the resultant novel electrode delivers a large reversible specific capacity of 637.2 mAh g⁻¹ at a high rate of 1C. Such superior capacity may benefit from rational design based on structural engineering to boost synergistic effects of the integrated electrode. The outer shell with the ultrathin 2D nanoarchitecture blocks can provide favourable Li⁺ lateral intercalation lengths and more beneficial transport routes for electrolyte ions, with sufficient void space among the nanosheets to buffer the volume expansion. Furthermore, the interconnected 1D micro-fibre core with outstanding metallic conductivity can offer an efficient electron transport pathway along axial orientation to shorten electron transport. More importantly, the metal’s remarkable flexibility and high tensile strength provide the hybrid integrated electrode with strong bending and stretchability relative to sintered carbon or graphene hosts. The presented strategy demonstrates that this rational nanoarchitecture design based on integrated engineering is an effective route to maintain the structural stability of electrodes in flexible LIBs. Full article

(This article belongs to the Special Issue Electrocatalysts for Oxygen/Hydrogen-Involved Reactions)

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9 pages, 7955 KiB

Open AccessCommunication

Degradation Investigation of Electrocatalyst in Proton Exchange Membrane Fuel Cell at a High Energy Efficiency

by Jie Song, Qing Ye, Kun Wang, Zhiyuan Guo and Meiling Dou

Molecules 2021, 26(13), 3932; https://doi.org/10.3390/molecules26133932 - 28 Jun 2021

Cited by 8 | Viewed by 2522

Abstract

The development of high efficient stacks is critical for the wide spread application of proton exchange membrane fuel cells (PEMFCs) in transportation and stationary power plant. Currently, the favorable operation conditions of PEMFCs are with single cell voltage between 0.65 and 0.7 V, [...] Read more.

The development of high efficient stacks is critical for the wide spread application of proton exchange membrane fuel cells (PEMFCs) in transportation and stationary power plant. Currently, the favorable operation conditions of PEMFCs are with single cell voltage between 0.65 and 0.7 V, corresponding to energy efficiency lower than 57%. For the long term, PEMFCs need to be operated at higher voltage to increase the energy efficiency and thus promote the fuel economy for transportation and stationary applications. Herein, PEMFC single cell was investigated to demonstrate its capability to working with voltage and energy efficiency higher than 0.8 V and 65%, respectively. It was demonstrated that the PEMFC encountered a significant performance degradation after the 64 h operation. The cell voltage declined by more than 13% at the current density of 1000 mA cm⁻², due to the electrode de-activation. The high operation potential of the cathode leads to the corrosion of carbon support and then causes the detachment of Pt nanoparticles, resulting in significant Pt agglomeration. The catalytic surface area of cathode Pt is thus reduced for oxygen reduction and the cell performance decreased. Therefore, electrochemically stable Pt catalyst is highly desirable for efficient PEMFCs operated under cell voltage higher than 0.8 V. Full article

(This article belongs to the Special Issue Electrocatalysts for Oxygen/Hydrogen-Involved Reactions)

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9 pages, 3514 KiB

Open AccessArticle

Fabrication of Highly Textured 2D SnSe Layers with Tunable Electronic Properties for Hydrogen Evolution

by Qianyu Zhou, Mengya Wang, Yong Li, Yanfang Liu, Yuanfu Chen, Qi Wu and Shifeng Wang

Molecules 2021, 26(11), 3319; https://doi.org/10.3390/molecules26113319 - 1 Jun 2021

Cited by 9 | Viewed by 3105

Abstract

Hydrogen is regarded to be one of the most promising renewable and clean energy sources. Finding a highly efficient and cost-effective catalyst to generate hydrogen via water splitting has become a research hotspot. Two-dimensional materials with exotic structural and electronic properties have been [...] Read more.

Hydrogen is regarded to be one of the most promising renewable and clean energy sources. Finding a highly efficient and cost-effective catalyst to generate hydrogen via water splitting has become a research hotspot. Two-dimensional materials with exotic structural and electronic properties have been considered as economical alternatives. In this work, 2D SnSe films with high quality of crystallinity were grown on a mica substrate via molecular beam epitaxy. The electronic property of the prepared SnSe thin films can be easily and accurately tuned in situ by three orders of magnitude through the controllable compensation of Sn atoms. The prepared film normally exhibited p-type conduction due to the deficiency of Sn in the film during its growth. First-principle calculations explained that Sn vacancies can introduce additional reactive sites for the hydrogen evolution reaction (HER) and enhance the HER performance by accelerating electron migration and promoting continuous hydrogen generation, which was mirrored by the reduced Gibbs free energy by a factor of 2.3 as compared with the pure SnSe film. The results pave the way for synthesized 2D SnSe thin films in the applications of hydrogen production. Full article

(This article belongs to the Special Issue Electrocatalysts for Oxygen/Hydrogen-Involved Reactions)

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