High Mass Energy Density Research Articles

Structure-Function Relationship of p-Block Bismuth for Selective Photocatalytic CO2 Reduction.

Selective photocatalytic reduction of CO2 to value-added fuels, such as CH4, is highly desirable due to its high mass-energy density. Nevertheless, achieving selective CH4 with higher production yield on p-block materials is hindered by non-ideal adsorption of *CHO key intermediate and an unclear structure-function relationship. Herein, we unlock the key reaction steps of CO2 and found a volcano-type structure-function relationship for photocatalytic CO2-to-CH4 conversion by gradual reduction of the p-band center of the p-block Bi element leading to formation of Bi-oxygen vacancy heterosites. The selectivity of CH4 is also positive correlation with adsorption energy of *CHO. The Bi-oxygen vacancy heterosites with an appropriate filled Bi-6p orbital electrons and p band center (-0.64) enhance the coupling between C-2p of *CHO and Bi-6p orbitals, thereby resulting in high selectivity (95.2 %) and productivity (17.4 μmol g-1 h-1) towards CH4. Further studies indicate that the synergistic effect between Bi-oxygen vacancy heterosites reduces Gibbs free energy for *CO-*CHO process, activates the C-H and C=O bonds of *CHO, and facilitates the enrichment of photoexcited electrons at active sites for multielectron photocatalytic CO2-to-CH4 conversion. This work provides a new perspective on developing p-block elements for selective photocatalytic CO2 conversion.

Robust Graphene-based Aerogel for Integrated 3D Asymmetric Supercapacitors with High Energy Density.

Three-dimensional asymmetric supercapacitors (3D ASC) have garnered significant attention due to their high operating window, theoretical energy density, and circularity. However, the practical application of 3D electrode materials is limited by brittleness and excessive dead volume. Therefore, we propose a controlled contraction strategy that regulates the pore structure of 3D electrode materials, eliminates dead volume in the 3D skeleton structure, and enhances mechanical strength. In this study to obtain reduced graphene oxide/manganese dioxide (rGO/MnO2) and reduced graphene oxide/carbon nanotube (rGO/CNT) composite aerogels with a stable and compact structure. MnO2 and CNT as nanogaskets, preventing the self-stacking of graphene nanosheets during the shrinkage process. Additionally, the high specific capacitor nanogaskets significantly enhance the specific energy density of the rGO aerogel electrode. The prepared rGO/MnO2//rGO/CNT 3D ASC exhibits a high mass-specific capacitance of 216.15 F g-1, a high mass energy density of 74 Wh kg-1 at 3.5 A g-1, and maintains a retention rate of capacitance at 99.89 % after undergoing 10,000 cycles of charge and discharge at 5 A g-1. The versatile and integrated assembly of 3D ASC units is achieved through the utilization of the robust mechanical structure of rGO-based aerogel electrodes, employing a mortise and tenon structural design.

Synthesis of P-(NiCo)CO3/TiO2/Ti Self-Supported Electrode with High Catalytic Activity and Stability for Hydrogen Evolution.

Hydrogen is considered an ideal clean energy due to its high mass-energy density, and only water is generated after combustion. Water electrolysis is a sustainable method of obtaining a usable amount of pure hydrogen among the various hydrogen production methods. However, its development is still limited by applying expensive noble metal catalysts. Here, the dissolution-recrystallization process of TiO2 nanotube arrays in water with the hydrothermal reaction of a typical nickel-cobalt hydroxide synthesis process followed by phosphating to prepare a self-supported electrode with (NiCo)CO3/TiO2 heterostructure named P-(NiCo)CO3/TiO2/Ti electrode is combined. The electrode exhibits an ultra-low overpotential of 31mV at 10mA cm-2 with a Tafel slope of 46.2mVdec-1 in 1m KOH and maintained its stability after running for 500h in 1m KOH. The excellent catalytic activity can be attributed to the structure of nanotube arrays with high specific surface area, superhydrophilicity, and super aerophobicity on the electrode surface. In addition, the uniform (NiCo)CO3/TiO2 heterostructure also accelerates the electron transfer on the electrode surface. Finally, DFT calculations demonstrate that phosphating also improves the ΔGH* and ΔGH2O of the electrode. The synthesis strategy also promotes the exploration of catalysts for other necessary electrocatalytic fields.

Development of a powerful miniature hydrogen catalytic combustion powered thermoelectric generator

Rapid development of portable electronics promotes the R&D of micro/miniature power sources with high energy density. The high mass energy density and zero emission characteristic of hydrogen show a huge potential to develop powerful portable hydrogen-based power sources. A miniature hydrogen catalytic combustion powered thermoelectric generator (CCP-TEG) is designed and tested in detail. An outstanding catalytic core is prepared with a newly proposed method on the basis of combining H2PtCl6 solution and foamed transition metal. Such catalytic core is demonstrated to provide high combustion temperature, complete combustion, and sufficient heat flux for power generation. Several parameters including input power, equivalent ratio, cooling mode, and load resistance are investigated to clarify their influences on the combustion temperature, electric power, and various efficiencies (combustion, heat collection, TE, and overall efficiencies) of the hydrogen CCP-TEG. The developed hydrogen CCP-TEG is able to generate an electric power of 20.7 W with an overall efficiency of 2.04%, filling the research gap of generating large electric power (>10 W) with sufficiently high overall efficiency (>2%) in the research field of hydrogen CCP-TEG. The generated electric power and overall efficiency are much higher than those in previous hydrogen CCP-TEGs. The prepared catalytic core remains excellent functionality after running for 30 h, and the combustion temperature is as high as 918 K, which ensures the sufficiently high temperature difference for powerful power generation. This study is conducted to illustrate a concrete method on developing a powerful hydrogen CCP-TEG, and to identify further research directions.

Modulation of *CHxO Adsorption to Facilitate Electrocatalytic Reduction of CO2 to CH4 over Cu-Based Catalysts

Copper (Cu) can efficiently catalyze the electrochemical CO2 reduction reaction (CO2RR) to produce value-added fuels and chemicals, among which methane (CH4) has drawn attention due to its high mass energy density. However, the linear scaling relationship between the adsorption energies of *CO and *CHxO on Cu restricts the selectivity toward CH4. Alloying a secondary metal in Cu provides a new freedom to break the linear scaling relationship, thus regulating the product distribution. This paper describes a controllable electrodeposition approach to alloying Cu with oxophilic metal (M) to steer the reaction pathway toward CH4. The optimized La5Cu95 electrocatalyst exhibits a CH4 Faradaic efficiency of 64.5%, with the partial current density of 193.5 mA cm-2. The introduction of oxophilic La could lower the energy barrier for *CO hydrogenation to *CHxO by strengthening the M-O bond, which would also promote the breakage of the C-O bond in *CH3O for the formation of CH4. This work provides a new avenue for the design of Cu-based electrocatalysts to achieve high selectivity in CO2RR through the modulation of the adsorption behaviors of key intermediates.

On the Physical Nature of Einstein’s Gravitational Lensing Effect

Gravitational lensing has become a powerful research tool for exploring the distribution of matter and energy in the universe nowadays, as glare phenomena around the Sun and massive galaxies are indeed observed on the Earth. What is the physical nature of gravitational lensing effect? Both Newton’s law of gravitation and Einstein’s theory of relativity are difficult to physically explain these glare phenomena. This study points out that the observed glare around the Sun and large galaxies is a result or product of the orthogonal interaction of high-energy particles emitted from different star light sources. It shows a new physical state associated with abnormal high mass-energy density.

Design and application of MOFs and derived composite materials inlithium-sulfur batteries

Against the background of increasingly prominent energy crisis and environmental problems, electrochemical energy storage technology has been developed rapidly. Among the competitors in the field of “beyond lithium” energy storage, lithium-sulfur batteries (Li-S) have become the most promising new energy storage technology owing to the advantages of high theoretical specific capacity, high mass energy density, environmental friendliness and low cost. However, there are still some bottleneck problems to be solved in the development of lithium-sulfur batteries, such as poor conductivity of cathode materials, polysulfide shuttle effect and electrode volume changes during charge and discharge. As the key components of lithium-sulfur batteries, the design and preparation of electrode and separator materials play the important roles in solving these problems and improving the overall performance of the batteries. Metal-organic frameworks (MOFs) and their derived composite materials exhibit the advantages of light weight, good electron and ion conductivity, abundant channels and uniform distribution of active sites to be used as electrode or separator modification materials for lithium-sulfur battery. In addition, this kind of composite material also possesses the characteristics of controllable morphology and composition, abundant source and adjustable pore size, which are convenient for mechanism research. Herein, we comprehensively introduce the composition, working mechanism and application of lithium-sulfur batteries. Importantly, we also review the research progress of MOFs and derivatives as cathode materials and separator materials in lithium-sulfur batteries in recent years. The prospects of the materials in improving the performance of lithium-sulfur batteries are also prospected.

A multifunctional hydrogel polyelectrolyte based flexible and wearable supercapacitor

To well satisfy the newly emerging personalized electronics, it is urgent to develop durable and reliable flexible energy storage devices having a favorable match with them. However, conventional polymer matrixs based hydrogel electrolytes inevitably limit the development of desired supercapacitors due to their poor stretchable, healable as well as electrochemical properties. Here, a novel multifunctional hydrogel polyelectrolyte (VHSNPs-PAA/H2SO4/ARS) is developed comprising the alizarin red S (ARS) redox mediator and the double cross-linked polyacrylic acid (PAA) by the vinyl hybrid silica nanoparticles (VHSNPs) and hydrogen bonds, which realized the combination of ultrahigh stretchability (~2400% strain), robust mechanical toughness (lift up the 500 g weights), favorable self-healability (~92% efficiency during 10 cutting/healing cycles), high ionic conductivity (33 mS cm−1), powerful self-adhesiveness and superior redox activity within a single hydrogel structure. The facilely fabricated carbon-based supercapacitor using the obtained hrdrogel as the electrolyte can achieve large electrode specific capacitance of 248 F g−1 and high mass energy density of 16.7 W h kg−1, which are much larger than the recently reported stretchable and self-healing hydrogel electrolytes based flexible supercapacitors. Meanwhile, as-fabricated device also exhibits the excellent cycling stability and superior durability against physical deformation after 5000 charge-discharge cycles and 200 bending-releasing cycles, respectively.

Hydrogen vs. Battery in the Long-term Operation. A Comparative Between Energy Management Strategies for Hybrid Renewable Microgrids

The growth of the world’s energy demand over recent decades in relation to energy intensity and demography is clear. At the same time, the use of renewable energy sources is pursued to address decarbonization targets, but the stochasticity of renewable energy systems produces an increasing need for management systems to supply such energy volume while guaranteeing, at the same time, the security and reliability of the microgrids. Locally distributed energy storage systems (ESS) may provide the capacity to temporarily decouple production and demand. In this sense, the most implemented ESS in local energy districts are small–medium-scale electrochemical batteries. However, hydrogen systems are viable for storing larger energy quantities thanks to its intrinsic high mass-energy density. To match generation, demand and storage, energy management systems (EMSs) become crucial. This paper compares two strategies for an energy management system based on hydrogen-priority vs. battery-priority for the operation of a hybrid renewable microgrid. The overall performance of the two mentioned strategies is compared in the long-term operation via a set of evaluation parameters defined by the unmet load, storage efficiency, operating hours and cumulative energy. The results show that the hydrogen-priority strategy allows the microgrid to be led towards island operation because it saves a higher amount of energy, while the battery-priority strategy reduces the energy efficiency in the storage round trip. The main contribution of this work lies in the demonstration that conventional EMS for microgrids’ operation based on battery-priority strategy should turn into hydrogen-priority to keep the reliability and independence of the microgrid in the long-term operation.

Investigating hydrogen evolution reaction properties of a new honeycomb 2D AlC

The hydrogen due to its high mass energy density is a new renewable, economically viable and clean resource. The most eco-friendly and economical approaches for the generation of hydrogen through hydrogen evolution is electrochemical water splitting. The two-dimensional (2D) nanomaterials have been recently found as potential candidates as non-noble metal catalyst for hydrogen evolution. In this work, we have systematically studied the structural and electronic properties of the newly predicted hexagonal-aluminium carbide monolayer (h-AlC ML) under the framework of dispersion-corrected density functional theory (DFT) calculations. The calculated electronic total density of states (TDOS) of h-AlC ML predict its metallic nature in contrast to other polar honeycomb 2D materials which are either semiconducting or semimetallic. The metallic behavior of h-AlC monolayer which motivates us to investigate its HER activity results due to the presence of delocalized charge density near Fermi level. Thus, we have investigated the HER activity of h-AlC ML by calculating hydrogen (H) adsorption energy (ΔEH) and Gibbs free energy (ΔGH) at three different sites of the 3 × 3 and 4 × 4 supercells of h-AlC ML; top of carbon atom (EH-C), top of aluminium atom (EH-Al) and hollow site (EH-Hollow). Our results show that the hollow site is most catalytically active site in both supercells of h-AlC ML. We believe that our results will inspire experimentalists to fabricate this new 2D material for achieving the desired range of HER activity.

Dynamic study of a new design of a tanks based on metallic hydrides

It is known that the hydrogen has a very high mass energy density, in fact, that it is a lightest gas; therefore, its storage is a great problem. The aim of the hydrogen storage technologies is thus to reduce the volume that hydrogen occupies in its thermodynamically stable state under conditions close to ambient salt. Recent work on hydrogen storage is mainly based on the use of metal hydrides. These metal hydrides have a high capacity for the hydrogen storage in the operating conditions. The effecting parameters on the performance of such a metal-hydrogen reactor are its design and configuration. In this case, there are a number of problems that need to be considered in designing a reactor. Among these parameters are the reactor configuration, the thermal and the mechanical strength, the kinetics of hydrogen storage and the security. Our study is concentrated on the problem of the thermal and the mechanical strength while focusing on the nature of the metal makes the reactor. In this work, the experimental studies of the hydrogen absorption phenomenon in different reactors, based on metal hydrides, were evaluated. The characteristics of the reaction kinetics in three different reactors using the same measurement conditions were compared. A numerical model describing the reaction kinetic of the H2 absorption by LaNi5 alloy validates the results were obtained. Of these results, it is found that the rate constant varies from one reactor to another. Moreover, the activation energy of the absorption kinetics were identified.

Review of sustainable solar hydrogen production using photon fuel on artificial leaf

Energy conversion from the renewable energy sources with suitable energy storage plays a vital role in the sustainable development. Sustainable hydrogen production from the solar energy is well suited for energy storage applications because of inherent high mass energy density of hydrogen. This manuscript reviewing the techniques required for the sustainable solar hydrogen production using photon fuel on artificial leaf, i.e. solar cell. The designing and assembling of artificial solar leaf, which is the replica of natural leaf and capable of harnessing full solar spectrum, are deliberated. This technology for sustainable solar hydrogen production will overlay a viable way for more real-world applications of traditional as well new generation solar cells, e.g. multi-junction solar cells coated with variable band gap of quantum materials, in the future. This, also, results in the successive control on carbon emission by converting abundantly present CO2/CO into meaningful future industrial fuel, therefore, generating hydrogen, known as photon fuel, via successfully harnessing the wide spectrum of the solar radiation.

Biomass-derived hierarchical porous carbons: boosting the energy density of supercapacitors via an ionothermal approach

High mass energy density coupled with high power density is highly desired for electrical double-layer capacitors.