The Loess Critical Zone (LCZ) is located in the intersection of bedrock, groundwater, pedosphere, atmosphere and biosphere. It is a key issue to understand the structural characteristics and soil carbon (C) cycle of the LCZ. We summarized the mechanisms of C exchange between rocks and the atmosphere, and discussed the mechanisms of C stabilization and persistence of the LCZ. Due to the deep layer, C stocks of the CLZ could be underestimated. In light of the recent theory of microbial C pump, soil microorganisms play an important role in C cycle, however, the microbial function is not widely considered in C cycling model of the LCZ. For future studies, it is suggested to systematically study the C cycling process from plant canopy to bedrock by the framework system of the LCZ. A variety of techniques and methods are integrated to combine short-term and high-frequency observations with long-term positioning observations, and pay attention to the response and feedback mechanisms of soil organic C (SOC) cycling to global changes and human activities, especially the migration and transformation of SOC in each circle and interface of the LCZ. We also recommend the necessity for intensive and long-term C monitoring in LCZ over broad geographic scale, to improve microbial C model for accurately evaluating terrestrial C budget and its dynamics. Altogether, this is the first review of C cycling, spanning from the land surface down to the bedrock in the LCZ, which is significant implications for biogeochemical cycling of C in surface and deep layers down to the bedrock.
The utilization of biochar derived from biomass residue to enhance anaerobic digestion (AD) for bioenergy recovery offers a sustainable approach to advance sustainable energy and mitigate climate change. However, conducting comprehensive research on the optimal conditions for AD experiments with biochar addition poses a challenge due to diverse experimental objectives. Machine learning (ML) has demonstrated its effectiveness in addressing this issue. Therefore, it is essential to provide an overview of current ML-optimized energy recovery processes for biochar-enhanced AD in order to facilitate a more systematic utilization of ML tools. This review comprehensively examines the material and energy flow of biochar preparation and its impact on AD is comprehension reviewed to optimize biochar-enhanced bioenergy recovery from a production process perspective. Specifically, it summarizes the application of the ML techniques, based on artificial intelligence, for predicting biochar yield and properties of biomass residues, as well as their utilization in AD. Overall, this review offers a comprehensive analysis to address the current challenges in biochar utilization and sustainable energy recovery. In future research, it is crucial to tackle the challenges that hinder the implementation of biochar in pilot-scale reactors. It is recommended to further investigate the correlation between the physicochemical properties of biochar and the bioenergy recovery process. Additionally, enhancing the role of ML throughout the entire biochar-enhanced bioenergy recovery process holds promise for achieving economically and environmentally optimized bioenergy recovery efficiency.
The potential for recycling graphitic carbon from lithium-ion battery (LIB) anodes has been overlooked due to its relatively low economic value in applications. This study proposed to use graphene nanoplates (GNPs), which were obtained from spent lithium battery anode graphite, treated with ball-milling method, for hydrothermal synthesis of MnO2-supported graphene nanoplates (MnO2/GNPs) composites materials. The composites exhibited excellent electrochemical characterization curves, indicating ideal capacitance characteristics. The analysis of MG24-20 material showed the good impact resistance and capacity retention around 100% with capacitance of 124.6F/g at 10 mV/s, surpassed similar samples using precious metals and high-end materials, enabling the reuse of spent graphite in energy conversion and storage system for effective utility.
Layered metal oxides are promising cathode materials for sodium-ion batteries (SIBs) due to their high theoretical specific capacity and wide Na+ diffusion channels. However, the irreversible phase transitions and cationic/anionic redoxes cause fast capacity decay. Herein, P2-type Na0.67Mg0.1Mn0.8Fe0.1O2 (NMMF-1) cathode material with moderate active Fe3+ doping has been designed for sodium storage. Uneven Mn3+/Mn4+distribution is observed in NMMF-1 and the introduction of Fe3+ is beneficial for reducing the Mn3+ contents both at the surface and in the bulk to alleviate the Jahn-Teller effect. The moderate Fe3+/Fe4+ redox can realize the best tradeoff between capacity and cyclability. Therefore, the NMMF-1 demonstrates a high capacity (174.7 mAh g−1 at 20 mA g−1) and improved cyclability (78.5% over 100 cycles) in a wide-voltage range of 1.5-4.5 V (vs. Na+/Na). In-situ X-ray diffraction reveals a complete solid-solution reaction with a small volume change of 1.7% during charge/discharge processes and the charge compensation is disclosed in detail. This study will provide new insights into designing high-capacity and stable layered oxide cathode materials for SIBs.
Demethoxylation was kinetically and spectroscopically studied over three catalysts with different Ru0/Ruδ+ ratios. In-situ spectroscopic tests demonstrated that the synergy between Ru0 and Ruδ+ was crucial, and Ru0 was in charge of H2 activation and adsorption of aromatic ring while Ruδ+ adsorbed with O in methoxyl. A Langmuir-Hinshelwood kinetic model was proposed, and ratio of Ru0/Ruδ+ was the key in deciding the rate-determining step (RDS): i) desorption of toluene was RDS over catalyst with high Ru0 ratio; ii) dissociation of H2 was RDS over Ruδ+ enriched catalyst; iii) demethoxylation was rate-determined by CO water-gas shift (WGS) when Ru0/Ruδ+ approached ~ 1. The best performance was obtained over Ru/NiAl2O4-200, which effectively enabled both C-O bond activation and rapid recovery of adsorption sites for aromatic rings. Finally, in-situ DRIFT studies on methoxy decomposition and CO-WGS unraveled that the electronic composition of Ru was more stable in Ru/NiAl2O4-200 which contributes to its excellence.
Sodium-ion batteries are considered one of the perspective alternatives to lithium-ion batteries due to their affordability and plentiful supply of sodium. However, traditional sodium-ion batteries that use organic electrolytes pose a threat to public safety and the ecological environment. As a result, aqueous electrolytes with high safety and cost-effectiveness are becoming more popular. Unfortunately, typically aqueous electrolytes face limitations in ionic conductivity and have relatively high freezing points, which hinder their ability to function at extremely low temperatures. These issues can be resolved with an easy-to-use method called electrolyte additive. The research on electrolyte additives for subzero-temperature aqueous sodium-ion batteries has not been systematically reviewed at present. This review aims to provide a comprehensive summary of the electrolyte additives for subzero-temperature aqueous sodium-ion batteries. Furthermore, the potential development paths of electrolyte additives to promote the advancement of electrochemical energy storage are also explored.
The implementation of sodium metal batteries (SMBs) is known for their low cost and high energy density. However, a major concern in SMBs is the formation of dendrites on the Na metal anode, which can potentially cause short circuits and compromise safety. Herein, to address this issue, we propose a novel approach to create a protective layer by decorating Na surface with NaI particles. This protective layer exhibits a high Young’s modulus and excellent sodium ion transference ability. As a result, the lifespan of the Na/NaI||Na/NaI cell is significantly extended to 850 h at 0.5 mA cm−2/1 mAh cm−2. Furthermore, when the Na/NaI anode is combined with a Na3V2(PO4)3 (NVP) cathode, the full cell retains 83 mAh g−1 (approximately 94% of its initial capacity) even after 1500 cycles at 5 C. Overall, this work presents a simple and effective method for establishing a protective layer on the Na surface, thereby enabling the realization of long lifespan and stable SMBs.
The state of New York admitted 143 million metric tons of carbon emissions from fossil fuels in 2020, prompting the ambitious goal set by the CLCPA to achieve carbon neutrality. The paper focused on analyzing and predicting carbon emissions using four different machine-learning algorithms. It examined emissions from fossil fuel combustion from 1990 to 2020 and validated four different algorithms to choose the most effective one for predicting emissions from 2020 to 2050. The analysis covered various economic sectors including transportation, residential, commercial, industrial, and electric power. By analyzing policies, the paper forecasted emissions for 2030 and 2050, leading to the identification of different pathways to reach carbon neutrality. The research concluded that in order to achieve neutrality, radical measures must be taken by the state of New York. Additionally, the paper compared the most recent data for 2021 with the forecasts, showing that significant measures need to be implemented to achieve the goal of carbon neutrality. Despite some studies assuming a trend of decreased emissions, the research revealed different results. The paper presents three pathways, two of which follow the ambitious plan to reach carbon neutrality. As a result, the emission amount by 2050 for the different pathways was projected to be 31.1, 22.4, and 111.95 of MMt CO2 e, showcasing the need for urgent action to combat climate change.
The conversion of CO2 into fuels and valuable chemicals presents a viable path toward carbon neutrality. The aim of this study is to investigate the potential of metal-doped graphene catalysts in the reduction of CO2 to C1 products. 20 typical M-graphene (M = metal) catalysts were established based on DFT calculations. Six candidate catalysts, i.e., V-, Cr-, Mn-, Ni-, Mo-, and Ta-graphene catalysts, were selected by combining the hydrogen dissociation ability and the energy band gap of the catalysts. Subsequently, the adsorption characteristics and hydrogenation reactions of CO2 over the six candidates were explored. CO2 tends to adsorb at the M site through vertical adsorption and carbon-oxygen co-adsorption. V- and Cr-graphene catalysts promote the production of intermediate COOH, whereas Mn-, Ni-, Mo-, and Ta-doped surfaces are more favorable for HCOO formation. Concerning the hydrogenation to CO and HCOOH, V-, Cr-, Ni- and Mo-graphene catalysts preferentially yield CO from COOH, whereas Ta-doped graphene favors the formation of HCOOH. In total, the competitive hydrogenation of CO2 reveals the selectivity of the C1 products. Cr- and Ni-graphene favor the production of HCOOH and CH3OH, whereas V-, Mn-, Mo-, and Ta-graphene primarily yield CH3OH.
Heat pumps are a solution for decarbonising home heating in the UK. However, the readiness of UK homes for heat pumps is an area of concern regarding the policies aimed at increasing heat pump adoption. This work combines multiple perspectives in evaluating the technical readiness of homes with the market readiness of installers and homeowners to proceed with installing heat pumps. The effectiveness of past heating and energy efficiency policies in the UK are reviewed, along with building regulations, incentives to promote energy efficiency and the effectiveness of heat pump technology in heating homes. Current policies support the cost of a heat pump but home improvements to make homes ‘heat pump-ready’ can be necessary to achieve optimal heat pump system performance.
Thermal-integrated pumped thermal electricity storage (TI-PTES) could realize efficient energy storage for fluctuating and intermittent renewable energy. However, the boundary conditions of TI-PTES may frequently change with the variation of times and seasons, which causes a tremendous deterioration to the operating performance. To realize efficient and flexible energy storage in operating conditions, a novel composition-adjustable TI-PTES is proposed, and the operating performance is investigated and compared with composition-fixed TI-PTES. Simulation results show that, compared to composition-fixed TI-PTES, the energy storage efficiency of TI-PTES could be enhanced by the absolute value of 4.4-18.3% by introducing composition adjustment method under various boundary conditions. Besides, tuning sub-system composition could simultaneously adjust the capacities of power input, heat storage and power output, realizing a more flexible operating range for TI-PTES. A case study for an isolated energy community shows that composition-adjustable TI-PTES could realize 100% conversion of off-peak electric energy and reduce daily investment by 35.6% compared with composition-fixed TI-PTES.
Multi-stage reverse electrodialysis (MSRED) offers a promising way for efficient salinity gradient energy harvesting. Here, an improved model of the MSRED system under serial control strategy is proposed. The technical-economic analysis is conducted with considering discount, depreciation and different regional tax and electricity price levels under the maximum net power output conditions. Results reveal that net power output and energy efficiency both increase first with increasing stage numbers, reach their maximum values, and then decrease. For 5 M/0.05 M solutions, the optimal net power output of 4.98 kW is obtained at the stage number n = 12. The optimal stage number corresponding to the maximum net power increases with increasing feed solution concentrations. Due to the compromise between net power generation and capital cost, there exist optimal stage numbers leading to the lowest LCOE and largest NPV, respectively. Higher feed solution concentration can significantly decrease the system LCOE and increase the NPV. The optimal stage number corresponding to the maximum NPV increases with increasing feed solution concentrations. In Germany, for 5 M/0.05 M solutions, the lowest LCOE of 0.061 €·kWh−1 is achieved at n = 3 while the highest NPV over the system lifecycle of 52,005 € is obtained at n = 8. Lower tax, higher electricity price, appropriate membrane price and stage numbers, and high salinity gradient sources can significantly accelerate the commercial completeness of the MSRED systems.
Ammonia is emerging as a viable alternative to fossil fuels in combustion systems, aiding in the reduction of carbon emissions. However, its use faces challenges, including NOx emissions and low flame speed. Innovative approaches and technologies have significantly advanced the development and implementation of ammonia as a zero-carbon fuel. This review explores current advancements in using ammonia as a fuel substitute, highlighting the complexities that various systems need to overcome before reaching full commercial maturity in support of practical decarbonising global strategies. Different from other reviews, this article incorporates insights of various industrial partners currently working towards green ammonia technologies. The work further addresses fundamental complexities of ammonia combustion, crucial for its practical and industrial implementation in various types of equipment.
Improving the performance of proton exchange membrane fuel cells (PEMFCs) requires deep understanding of the reactive transport processes inside the catalyst layers (CLs). In this study, a particle-overlapping model is developed for accurately describing the hierarchical structures and oxygen reactive transport processes in CLs. The analytical solutions derived from this model indicate that carbon particle overlap increases ionomer thickness, reduces specific surface areas of ionomer and carbon, and further intensifies the local oxygen transport resistance (Rother). The relationship between Rother and roughness factor predicted by the model in the range of 800-1600 s m-1 agrees well with the experiments. Then, a multiscale model is developed by coupling the particle-overlapping model with cell-scale models, which is validated by comparing with the polarization curves and local current density distribution obtained in experiments. The relative error of local current density distribution is below 15% in the ohmic polarization region. Finally, the multiscale model is employed to explore effects of CL structural parameters including Pt loading, I/C, ionomer coverage and carbon particle radius on the cell performance as well as the phase-change-induced (PCI) flow and capillary-driven (CD) flow in CL. The result demonstrates that the CL structural parameters have significant effects on the cell performance as well as the PCI and CD flows. Optimizing the CL structure can increase the current density and further enhance the heat-pipe effect within the CL, leading to overall higher PCI and CD rates. The maximum increase of PCI and CD rates can exceed 145%. Besides, the enhanced heat-pipe effect causes the reverse flow regions of PCI and CD near the CL/PEM interface, which can occupy about 30% of the CL. The multiscale model significantly contributes to a deep understanding of reactive transport and multiphase heat transfer processes inside PEMFCs.
A particle-overlapping model for reactive transport process in catalyst layers.
A multiscale model coupling particle-overlapping model with cell-scale models.
The model is rigorously validated from nanoscale to commercial-cell scale.
Effects of catalyst layer structures on cell performance are evaluated.
Phase-change-induced and capillary-driven flows in catalyst layers are studied.
