Editorial

4 pages, 214 KiB

Open AccessEditorial

Hydrogenation and Dehydrogenation of Liquid Organic Hydrogen Carriers: A New Opportunity for Carbon-Based Catalysts

by Salvador Ordóñez, Eva Díaz and Laura Faba

C 2022, 8(1), 7; https://0-doi-org.brum.beds.ac.uk/10.3390/c8010007 - 13 Jan 2022

Cited by 4 | Viewed by 3656

The development of a hydrogen-based economy is the perfect nexus between the need of discontinuing the use of fossil fuels (trying to mitigate climate change), the development of a system based on renewable energy (with the use of hydrogen allowing us to buffer [...] Read more.

The development of a hydrogen-based economy is the perfect nexus between the need of discontinuing the use of fossil fuels (trying to mitigate climate change), the development of a system based on renewable energy (with the use of hydrogen allowing us to buffer the discontinuities produced in this generation) and the achievement of a local-based robust energy supply system [...] Full article

(This article belongs to the Special Issue Carbon Materials for Physical and Chemical Hydrogen Storage)

Research

Jump to: Editorial, Review

13 pages, 2296 KiB

Open AccessArticle

On the Problem of “Super” Storage of Hydrogen in Graphite Nanofibers

by Yury S. Nechaev, Evgeny A. Denisov, Alisa O. Cheretaeva, Nadezhda A. Shurygina, Ekaterina K. Kostikova, Andreas Öchsner and Sergei Yu. Davydov

C 2022, 8(2), 23; https://0-doi-org.brum.beds.ac.uk/10.3390/c8020023 - 29 Mar 2022

Cited by 2 | Viewed by 2404

Abstract

This article is devoted to some fundamental aspects of “super” storage in graphite nanofibers (GNF) of “reversible” (~20–30 wt.%) and “irreversible” hydrogen (~7–10 wt.%). Extraordinary results for hydrogen “super” storage were previously published by the group of Rodriguez and Baker at the turn [...] Read more.

This article is devoted to some fundamental aspects of “super” storage in graphite nanofibers (GNF) of “reversible” (~20–30 wt.%) and “irreversible” hydrogen (~7–10 wt.%). Extraordinary results for hydrogen “super” storage were previously published by the group of Rodriguez and Baker at the turn of the century, which been unable to be reproduced or explained in terms of physics by other researchers. For the first time, using an efficient method of processing and analysis of hydrogen thermal desorption spectra, the characteristics of the main desorption peak of “irreversible” hydrogen in GNF were determined: the temperature of the highest desorption rate (T_max = 914–923 K), the activation energy of the desorption process (Q ≈ 40 kJ mol⁻¹), the pre-exponential rate constant factor (K₀ ≈ 2 × 10⁻¹ s⁻¹), and the amount of hydrogen released (~8 wt.%). The physics of hydrogen “super” sorption includes hydrogen diffusion, accompanied by the “reversible” capture of the diffusant by certain sorption “centers”; the hydrogen spillover effect, which provides local atomization of gaseous H₂ during GNF hydrogenation; and the Kurdjumov phenomenon on thermoelastic phase equilibrium. It is shown that the above-mentioned extraordinary data on the hydrogen “super” storage in GNFs are neither a mistake nor a mystification, as most researchers believe. Full article

(This article belongs to the Special Issue Carbon Materials for Physical and Chemical Hydrogen Storage)

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14 pages, 1818 KiB

Open AccessArticle

Experimental Volumetric Hydrogen Uptake Determination at 77 K of Commercially Available Metal-Organic Framework Materials

by Jose A. Villajos

C 2022, 8(1), 5; https://0-doi-org.brum.beds.ac.uk/10.3390/c8010005 - 05 Jan 2022

Cited by 8 | Viewed by 4115

Abstract

Storage is still limiting the implementation of hydrogen as an energy carrier to integrate the intermittent operation of renewable energy sources. Among different solutions to the currently used compressed or liquified hydrogen systems, physical adsorption at cryogenic temperature in porous materials is an [...] Read more.

Storage is still limiting the implementation of hydrogen as an energy carrier to integrate the intermittent operation of renewable energy sources. Among different solutions to the currently used compressed or liquified hydrogen systems, physical adsorption at cryogenic temperature in porous materials is an attractive alternative due to its fast and reversible operation and the resulting reduction in storage pressure. The feasibility of cryoadsorption for hydrogen storage depends mainly on the performance of the used materials for the specific application, where metal-organic frameworks or MOFs are remarkable candidates. In this work, gravimetric and volumetric hydrogen uptakes at 77 K and up to 100 bar of commercially available MOFs were measured since these materials are made from relatively cheap and accessible building blocks. These materials also show relatively high porous properties and are currently near to large-scale production. The measuring device was calibrated at different room temperatures to calculate an average correction factor and standard deviation so that the correction deviation is included in the measurement error for better comparability with different measurements. The influence of measurement conditions was also studied, concluding that the available adsorbing area of material and the occupied volume of the sample are the most critical factors for a reproducible measurement, apart from the samples’ preparation before measurement. Finally, the actual volumetric storage density of the used powders was calculated by directly measuring their volume in the analysis cell, comparing that value with the maximum volumetric uptake considering the measured density of crystals. From this selection of commercial MOFs, the materials HKUST-1, PCN-250(Fe), MOF-177, and MOF-5 show true potential to fulfill a volumetric requirement of 40 g·L⁻¹ on a material basis for hydrogen storage systems without further packing of the powders. Full article

(This article belongs to the Special Issue Carbon Materials for Physical and Chemical Hydrogen Storage)

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16 pages, 7817 KiB

Open AccessArticle

Effects of Reducing Agent on the Activity of PtRu/Carbon Black Anode Catalyst of Direct Methanol Fuel Cell

by Yu-Wen Chen and Han-Gen Chen

C 2021, 7(4), 72; https://0-doi-org.brum.beds.ac.uk/10.3390/c7040072 - 19 Oct 2021

Viewed by 2234

Abstract

A series of PtRu/carbon black catalysts were prepared by means of deposition-precipitation and reduced by various reducing agents. NaBH₄, HCHO and NaH₂PO₂, respectively, were used as the reduction agents. Some of the samples were reduced by various [...] Read more.

A series of PtRu/carbon black catalysts were prepared by means of deposition-precipitation and reduced by various reducing agents. NaBH₄, HCHO and NaH₂PO₂, respectively, were used as the reduction agents. Some of the samples were reduced by various amounts of NaH₂PO₂ to investigate the effects of P/Pt ratios on the characteristics and activity of the catalyst. These catalysts were characterized by X-ray diffraction and transmission electron microscopy. The components of these catalysts were detected by X-ray fluorescence, X-ray photoelectron microscopy, and extended X-ray absorption of fine structures (EXAFS). The methanol oxidation ability of the catalysts was tested by cyclic voltammetry measurement. The results show that NaH₂PO₂ could effectively reduce the particle size of PtRu metal. It can suppress the growth of metal particles. In addition, the P/Pt ratio is crucial. The catalyst reduced by NaH₂PO₂ with a P/Pt ratio of 1.2 had the highest activity among all catalysts. It had the higher Pt and Ru metal contents and smaller metal particle size than the other catalysts. Its activity was 253.12 A/g, which is higher that than the commercial catalyst (Johnson Matthey H10100, 251.32 A/g). Full article

(This article belongs to the Special Issue Carbon Materials for Physical and Chemical Hydrogen Storage)

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15 pages, 5153 KiB

Open AccessArticle

CH Activation by a Heavy Metal Cation: Production of H₂ from the Reaction of Acetylene with C₄H₄-Os(+) in Gas phase

by Zikri Altun, Erdi Ata Bleda and Carl Trindle

C 2021, 7(4), 68; https://0-doi-org.brum.beds.ac.uk/10.3390/c7040068 - 30 Sep 2021

Viewed by 2188

Abstract

While first-row transition metal cations, notably Fe(+), catalyze the gas-phase conversion of acetylene to benzene, a distinct path is chosen in systems with Os, Ir, and Rh cations. Rather than losing the metal cation M(+) from the benzene–M(+) complex, as is observed for [...] Read more.

While first-row transition metal cations, notably Fe(+), catalyze the gas-phase conversion of acetylene to benzene, a distinct path is chosen in systems with Os, Ir, and Rh cations. Rather than losing the metal cation M(+) from the benzene–M(+) complex, as is observed for the Fe(+) system, the heavy metal ions activate CH bonds. The landmark system C₄H₄-Os(+) reacts with acetylene to produce C₆H₄-Os(+) and dihydrogen. Following our work on isomers of the form C_2nH_2n-Fe(+), we show by DFT modeling that the CH bonds of the metalla-7-cycle structure, C₆H₆-Os(+), are activated and define the gas-phase reaction path by which H₂ is produced. The landmark structures on the network of reaction paths can be used as a basis for the discussion of reactions in which a single Os atom on an inert surface can assist reactions of hydrocarbons. Full article

(This article belongs to the Special Issue Carbon Materials for Physical and Chemical Hydrogen Storage)

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14 pages, 3105 KiB

Open AccessArticle

Biomass-Derived Carbons as Versatile Materials for Energy-Related Applications: Capacitive Properties vs. Oxygen Reduction Reaction Catalysis

by Stefan Breitenbach, Nemanja Gavrilov, Igor Pašti, Christoph Unterweger, Jiri Duchoslav, David Stifter, Achim Walter Hassel and Christian Fürst

C 2021, 7(3), 55; https://0-doi-org.brum.beds.ac.uk/10.3390/c7030055 - 24 Jul 2021

Cited by 8 | Viewed by 2249

Abstract

Biomass-derived carbons are very attractive materials due to the possibility of tuning their properties for different energy-related applications. Various pore sizes, conductivities and the inherent presence of heteroatoms make them attractive for different electrochemical reactions, including the implementation of electrochemical capacitors or fuel [...] Read more.

Biomass-derived carbons are very attractive materials due to the possibility of tuning their properties for different energy-related applications. Various pore sizes, conductivities and the inherent presence of heteroatoms make them attractive for different electrochemical reactions, including the implementation of electrochemical capacitors or fuel cell electrodes. This contribution demonstrates how different biomass-derived carbons prepared from the same precursor of viscose fibers can reach appreciable capacitances (up to 200 F g⁻¹) or a high selectivity for the oxygen reduction reaction (ORR). We find that a highly specific surface area and a large mesopore volume dominate the capacitive response in both aqueous and non-aqueous electrolytic solutions. While the oxygen reduction reaction activity is not dominated by the same factors at low ORR overpotentials, these take the dominant role over surface chemistry at high ORR overpotentials. Due to the high selectivity of the O₂ reduction to peroxide and the appreciable specific capacitances, it is suggested that activated carbon fibers derived from viscose fibers are an attractive and versatile material for electrochemical energy conversion applications. Full article

(This article belongs to the Special Issue Carbon Materials for Physical and Chemical Hydrogen Storage)

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Review

Jump to: Editorial, Research

21 pages, 3855 KiB

Open AccessReview

Hydrogen Storages Based on Graphene Nano-Flakes: Density Functional Theory Approach

by Hiroto Tachikawa

C 2022, 8(3), 36; https://0-doi-org.brum.beds.ac.uk/10.3390/c8030036 - 27 Jun 2022

Cited by 5 | Viewed by 1996

Abstract

Carbon materials such as graphene, carbon nanotubes, fullerene, and graphene nanoflakes (GNFs) are used for hydrogen storage. The doping of alkali metals to these materials generally increases the accumulation density of molecular hydrogen (H₂). However, the reason why the doping enhances [...] Read more.

Carbon materials such as graphene, carbon nanotubes, fullerene, and graphene nanoflakes (GNFs) are used for hydrogen storage. The doping of alkali metals to these materials generally increases the accumulation density of molecular hydrogen (H₂). However, the reason why the doping enhances the ability of the H₂ storage of GNF is not clearly known, although there are some explanations. In addition, the information on the storage capacity of GNF is ambiguous. In the present review article, we introduce our recent theoretical studies on the interaction of GNF with H₂ molecules carried out to elucidate the mechanism of hydrogen storage in alkali-doped GNFs. As alkali metals, lithium (Li), sodium (Na), and potassium (K) were examined, and the abilities of hydrogen storage were discussed. Next, the mechanism of Li-diffusion on GNF, which plays a crucial role in Li-battery, was presented. There are several unanswered questions. In particular, does lithium diffuse randomly on GNF? Or is there a specific diffusion path? We present our study, which elucidates the factors governing lithium diffusion on GNF. If the dominant factor is known, it is possible to arbitrarily control the diffusion path of lithium. This will lead to the development of highly functional battery materials. Finally, the molecular design of H adsorption–desorption reversible storage devices based on GNF will be introduced. Elucidating the mechanism of hydrogen storage, Li-diffusion on GNF, and molecular design of storage device is important in understanding the current molecular devices and provide a deeper insight into materials chemistry. Full article

(This article belongs to the Special Issue Carbon Materials for Physical and Chemical Hydrogen Storage)

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18 pages, 1540 KiB

Open AccessReview

Review of Cryogenic Carbon Capture Innovations and Their Potential Applications

by Carolina Font-Palma, David Cann and Chinonyelum Udemu

C 2021, 7(3), 58; https://doi.org/10.3390/c7030058 - 29 Jul 2021

Cited by 50 | Viewed by 17111

Abstract

Our ever-increasing interest in economic growth is leading the way to the decline of natural resources, the detriment of air quality, and is fostering climate change. One potential solution to reduce carbon dioxide emissions from industrial emitters is the exploitation of carbon capture [...] Read more.

Our ever-increasing interest in economic growth is leading the way to the decline of natural resources, the detriment of air quality, and is fostering climate change. One potential solution to reduce carbon dioxide emissions from industrial emitters is the exploitation of carbon capture and storage (CCS). Among the various CO₂ separation technologies, cryogenic carbon capture (CCC) could emerge by offering high CO₂ recovery rates and purity levels. This review covers the different CCC methods that are being developed, their benefits, and the current challenges deterring their commercialisation. It also offers an appraisal for selected feasible small- and large-scale CCC applications, including blue hydrogen production and direct air capture. This work considers their technological readiness for CCC deployment and acknowledges competing technologies and ends by providing some insights into future directions related to the R&D for CCC systems. Full article

(This article belongs to the Special Issue Carbon Materials for Physical and Chemical Hydrogen Storage)

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