Frontiers in Energy最新文献

It has been widely reported that, for faceted nanocrystals, the two adjacent facets with different band levels contribute to promoted charge separation, and provide active sites for photocatalytic reduction and oxidation reaction, respectively. In such cases, only one family of facets can be used for photocatalytic hydrogen evolution. Herein, by using SrTiO₃ nanocrystals enclosed by {023} and {001} facets as a model photocatalyst, this paper proposed a strategy to achieve the full-facets-utilization of the nanocrystals for photocatalytic hydrogen via chemically depositing Pt nanoparticles on all facets. The photo-deposition experiment of CdS provided direct evidence to demonstrate that the {023} facets which were responsible for photooxidation reaction can be function-reversed for photocatalytic hydrogen evolution after depositing Pt nanoparticles, together with the {001} facets. Thus, the full-facets-utilization led to a much-improved activity for photocatalytic hydrogen, in contrast to those SrTiO₃ nanocrystals with only {001} facets deposited by Pt nanoparticles via a photo-deposition method.

Hydrogen production from photoelectrochemical (PEC) water splitting has been regarded as a promising way to utilize renewable and endless solar energy. However, semiconductor film grown on photoelectrode suffers from numerous challenges, leading to the poor PEC performance. Herein, a straightforward sol-gel method with the ligand-induced growth strategy was employed to obtain dense and homogeneous copper bismuthate photocathodes for PEC hydrogen evolution reaction. By various characterizations, it was found that the nucleation and surface growth of CuBi₂O₄ layer induced by 2-methoxyethanol ligand (2-CuBi₂O₄) demonstrated a decent crystallinity and coverage, as well as a large grain size and a low oxygen vacancy concentration, leading to the good ability of light absorption and carrier migration. Consequently, under simulated sunlight irradiation (AM1.5G, 100 mW/cm²), the 2-CuBi₂O₄ photocathode achieved an enhanced photocurrent density of −1.34 mA·cm⁻² at 0.4 V versus the reversible hydrogen electrode and a promising applied bias photon-to-current efficiency of 0.586%. This surface modification by ligand growth strategy will shed light on the future design of advanced photoelectrodes for PEC water splitting.

Production of hydrogen, one of the most promising alternative clean fuels, through catalytic conversion from fossil fuel is the most technically and economically feasible technology. Catalytic conversion of natural gas into hydrogen and carbon is thermodynamically favorable under atmospheric conditions. However, using noble metals as a catalyst is costly for hydrogen production, thus mandating non-noble metal-based catalysts such as Ni, Co, and Cu-based alloys. This paper reviews the various hydrogen production methods from fossil fuels through pyrolysis, partial oxidation, autothermal, and steam reforming, emphasizing the catalytic production of hydrogen via steam reforming of methane. The multicomponent catalysts composed of several nonnoble materials have been summarized. Of the Ni, Co, and Cu-based catalysts investigated in the literature, Ni/Al₂O₃ catalyst is the most economical and performs best because it suppresses the coke formation on the catalyst. To avoid carbon emission, this method of hydrogen production from methane should be integrated with carbon capture, utilization, and storage (CCUS). Carbon capture can be accomplished by absorption, adsorption, and membrane separation processes. The remaining challenges, prospects, and future research and development directions are described.

High entropy materials (HEMs) have developed rapidly in the field of electrocatalytic water-electrolysis for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) due to their unique properties. In particular, HEM catalysts are composed of many elements. Therefore, they have rich active sites and enhanced entropy stability relative to single atoms. In this paper, the preparation strategies and applications of HEM catalysts in electrochemical water-electrolysis are reviewed to explore the stabilization of HEMs and their catalytic mechanisms as well as their application in support green hydrogen production. First, the concept and four characteristics of HEMs are introduced based on entropy and composition. Then, synthetic strategies of HEM catalysts are systematically reviewed in terms of the categories of bottom-up and top-down. The application of HEMs as catalysts for electrochemical water-electrolysis in recent years is emphatically discussed, and the mechanisms of improving the performance of electrocatalysis is expounded by combining theoretical calculation technology and ex-situ/in situ characterization experiments. Finally, the application prospect of HEMs is proposed to conquer the challenges in HEM catalyst fabrications and applications.

The performance parameters for characterizing the electrocaloric effect are isothermal entropy change and the adiabatic temperature change, respectively. This paper reviews the electrocaloric effect of ferroelectric materials based on different theoretical models. First, it provides four different calculation scales (the first-principle-based effective Hamiltonian, the Landau-Devonshire thermodynamic theory, phase-field simulation, and finite element analysis) to explain the basic theory of calculating the electrocaloric effect. Then, it comprehensively reviews the recent progress of these methods in regulating the electrocaloric effect and the generation mechanism of the electrocaloric effect. Finally, it summarizes and anticipates the exploration of more novel electrocaloric materials based on the framework constructed by the different computational methods.

Transition metal sulfides are commonly studied as photocatalysts for water splitting in solar-to-fuel conversion. However, the effectiveness of these photocatalysts is limited by the recombination and restricted light absorption capacity of carriers. In this paper, a broad spectrum responsive In₂S₃/Bi₂S₃ heterojunction is constructed by in-situ integrating Bi₂S₃ with the In₂S₃, derived from an In-MOF precursor, via the high-temperature sulfidation and solvothermal methods. Benefiting from the synergistic effect of wide-spectrum response, effective charge separation and transfer, and strong heterogeneous interfacial contacts, the In₂S₃/Bi₂S₃ heterojunction demonstrates a rate of 0.71 mmol/(g·h), which is 2.2 and 1.7 times as much as those of In₂S₃ (0.32 mmol/(g·h) and Bi₂S₃ (0.41 mmol/(g·h)), respectively. This paper provides a novel idea for rationally designing innovative heterojunction photocatalysts of transition metal sulfides for photocatalytic hydrogen production.

Lithium (Li) metal is believed to be the “Holy Grail” among all anode materials for next-generation Li-based batteries due to its high theoretical specific capacity (3860 mAh/g) and lowest redox potential (−3.04 V). Disappointingly, uncontrolled dendrite formation and “hostless” deposition impede its further development. It is well accepted that the construction of three-dimensional (3D) composite Li metal anode could tackle the above problems to some extent by reducing local current density and maintaining electrode volume during cycling. However, most strategies to build 3D composite Li metal anode require either electrodeposition or melt-infusion process. In spite of their effectiveness, these procedures bring multiple complex processing steps, high temperature, and harsh experimental conditions which cannot meet the actual production demand in consideration of cost and safety. Under this condition, a novel method to construct 3D composite anode via simple mechanical modification has been recently proposed which does not involve harsh conditions, fussy procedures, or fancy equipment. In this mini review, a systematic and in-depth investigation of this mechanical deformation technique to build 3D composite Li metal anode is provided. First, by summarizing a number of recent studies, different mechanical modification approaches are classified clearly according to their specific procedures. Then, the effect of each individual mechanical modification approach and its working mechanisms is reviewed. Afterwards, the merits and limits of different approaches are compared. Finally, a general summary and perspective on construction strategies for next-generation 3D composite Li anode are presented.

The coal-to-liquid coupled with carbon capture, utilization, and storage technology has the potential to reduce CO₂ emissions, but its carbon footprint and cost assessment are still insufficient. In this paper, coal mining to oil production is taken as a life cycle to evaluate the carbon footprint and levelized costs of direct-coal-to-liquid and indirect-coal-to-liquid coupled with the carbon capture utilization and storage technology under three scenarios: non capture, process capture, process and public capture throughout the life cycle. The results show that, first, the coupling carbon capture utilization and storage technology can reduce CO₂ footprint by 28%–57% from 5.91 t CO₂/t oil of direct-coal-to-liquid and 24%–49% from 7.10 t CO₂/t oil of indirect-coal-to-liquid. Next, the levelized cost of direct-coal-to-liquid is 648–1027 $/t of oil, whereas that of indirect-coal-to-liquid is 653–1065 $/t of oil. When coupled with the carbon capture utilization and storage technology, the levelized cost of direct-coal-to-liquid is 285–1364 $/t of oil, compared to 1101–9793 $/t of oil for indirect-coal-to-liquid. Finally, sensitivity analysis shows that CO₂ transportation distance has the greatest impact on carbon footprint, while coal price and initial investment cost significantly affect the levelized cost of coal-to-liquid.