Clean Energy Conversion Technologies Research Articles

Exploring the Synergistic Potential: A Comprehensive Review of MXene-Based Composite Electrocatalysts

MXenes, a prominent category of 2D materials consisting of transition metal carbides, nitrides, and carbonitrides, have garnered significant interest since the introduction of Ti3C2Tx. This fascination arises from their exceptional attributes like their high special surface area, superb electrical conductivity, and remarkable mechanical strength. These qualities have established MXenes as top materials for electrocatalysis, a critical component of clean energy conversion technologies. Crucially, MXenes serve as the foundation for the next generation of electrocatalysts, aiming at high activity, selectivity, and sustainability.In electrocatalysis, MXene composites enhance the performance of various reactions, such as water splitting and fuel cell operations. When combined with metals, metal oxides, or other conductive materials, MXenes exhibit improved electrical conductivity and catalytic activity. These composites can achieve higher efficiency and selectivity in electrochemical reactions, making them suitable for sustainable energy applications. MXene composites also play an significant role in the development of supercapacitors, which are energy storage devices characterized by rapid charge and discharge capabilities. The high special surface area and excellent conductivity of MXenes increase charge storage and improve energy and power density. When MXene composites are mixed with materials such as polymers or other nanomaterials, they can further optimize these properties, leading to increased performance and longevity. Also in battery technology, MXene composites are used to improve the performance of anodes and cathodes. Their high capacity for ion storage and conduction contributes to higher energy density and faster charge/discharge rates. By combining MXenes with other materials, researchers are able to create advanced battery systems that overcome traditional limitations, resulting in batteries that are more efficient, durable, and capable of delivering higher performance. In this study MXene–Carbon composites, MXene-LDH composites, MXene-Polymer composites, MXene-MOF composites are reviewed and discussed. The versatility of MXenes is further enhanced when they are composited with various other materials. Such compositions allow for tailoring their innate properties, enabling a widespread range of applications. In terms of environmental implications, MXenes and their composites boast excellent reducibility, conductivity, and biocompatibility, making them very appropriate for use in environmental clean-up and protection applications.

Ni-Doped SFM Double-Perovskite Electrocatalyst for High-Performance Symmetrical Direct-Ammonia-Fed Solid Oxide Fuel Cells.

Ammonia has emerged as a promising fuel for solid oxide fuel cells (SOFCs) owing to its high energy density, high hydrogen content, and carbon-free nature. Herein, the electrocatalytic potential of a novel Ni-doped SFM double-perovskite (Sr1.9Fe0.4Ni0.1Mo0.5O6-δ) is studied, for the first time, as an alternative anode material for symmetrical direct-ammonia SOFCs. Scanning and transmission electron microscopy characterization has revealed the exsolution of Ni-Fe nanoparticles (NPs) from the parent Sr2Fe1.5Mo0.5O6 under anode conditions, and X-ray diffraction has identified the FeNi3 phase after exposure to ammonia at 800 °C. The active-exsolved NPs contribute to achieving a maximal ammonia conversion rate of 97.9% within the cell's operating temperatures (550-800 °C). Utilizing 3D-printed symmetrical cells with SFNM-GDC electrodes, the study demonstrates comparable polarization resistances and peak power densities of 430 and 416 mW cm-2 for H2 and NH3 fuels, respectively, with long-term stability and a negligible voltage loss of 0.48% per 100 h during ammonia-fed extended galvanostatic operation. Finally, the ammonia consumption mechanism is elucidated as a multistep process involving ammonia decomposition, followed by hydrogen oxidation. This study provides a promising avenue for improving the performance and stability of ammonia-based SOFCs for potential applications in clean energy conversion technologies.

Co-Co6Mo6C2 heterostructure grown on carbon nanofibers as tri-functional electrocatalyst for overall water splitting and rechargeable Zn-air batteries

The advancement of cost-effective and efficient electrocatalysts for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) is crucial for the progress of clean energy conversion and storage technologies. In this work, cobalt (Co) and cobalt-molybdenum (Mo) bimetallic carbide (Co6Mo6C2) heterostructure grown on carbon nanofibers (denoted as Co-Co6Mo6C2/CNFs) as tri-functional electrocatalyst were prepared by a four-step method. Benefiting from the electronic structure modulation between the heterostructure to improve the catalytic activity, Co-Co6Mo6C2/CNFs exhibits high catalytic activity for HER (91 mV @ 10 mA cm−2), OER (293 mV @ 10 mA cm−2) and ORR (E1/2=0.80 V). Moreover, Co-Co6Mo6C2/CNFs assembled overall water splitting electrolyzer achieves a current density of 10 mA cm−2 with a battery voltage of only 1.70 V and has long-term durability. Zn-air batteries (ZABs) based on Co-Co6Mo6C2/CNFs has a power density of 156.6 mW cm−2 with good stability. This study contributes to the development of inexpensive and efficient transition metal-based multifunctional electrocatalysts.

Modulating electron structure of active sites in high-entropy metal sulfide nanoparticles with greatly improved electrocatalytic performance for oxygen evolution reaction

Excellent oxygen evolution reaction (OER) electrocatalysts hold paramount significance for related clean energy conversion technologies. High-entropy materials have garnered significant interests because of their novel structures and unprecedented potentials in application. Herein, we successfully prepared a high-entropy metal sulfide catalyst, specifically (FeCoNiMnMo)Sx, through a facile method. The resulting catalyst exhibited a phase similar to CoS2 and its electrocatalytic activity was rigorously evaluated as an OER catalyst in 1 M KOH. Endowed by the synergistic effect and the modulation of electronic structures among the various metals, the (FeCoNiMnMo)Sx catalyst demonstrated exceptional water oxidation performances. Notably, it required only 290 mV of overpotential to reach 10 mA cm−2. This remarkable performance underscores the effectiveness of high-entropy sulfides as electrocatalysts. The present work supplied a new successful example for exploring the vast potential of high-entropy materials in electrocatalysis and other related fields.

Electronic modulation optimizes intermediate adsorption on Ni sites via coupling NiCo alloy in N-doped carbon dodecahedrons toward efficient hydrogen evolution reaction

Developing efficient, stable, and low-cost metal electrocatalysts for hydrogen evolution reaction (HER) is significant for clean energy conversion technology. Regulating the adsorption energy of H intermediates by modulating the electronic structure of the active sites of the electrocatalyst for approximating the equilibrium potential is of primality importance to overcoming the kinetic sluggishness of the HER, yet still represents a great challenge. Herein, we have reported a NiCo alloy electrocatalyst supported by an N-doped carbon dodecahedral substrate with a strong electron coupling between the NiCo alloy and NC to improve the obstacles of both activity and stability for HER. Benefiting from the above electron coupling effect, the Ni1Co2/NC catalyst exhibits enhanced HER activity and stability in an acid electrolyte. Specifically, the Ni1Co2/NC exhibits enhanced acid HER activity with a low overpotential of 114.7 mV at 10 mA cm−2 and robust stability with negligible activity decay after 5000 cycles, which are superior to its counterpart. Theoretical calculations revealed that the electron coupling between the NiCo alloy and NC could effectively moderate the electronic states of NiCo alloy, dramatically decreasing the free energy for H adsorption and leading to optimal adsorption/desorption of *H, thereby promoting the overall HER kinetics. This study provides a new perspective on constructing catalysts of HER with low-cost, well-designed structures and superior performance for clean energy conversion technology.

Gasification characteristics and sulfur migration mechanism during supercritical water partial oxidation of 2-methylthiophene

Supercritical water partial oxidation (SCWPO), as a clean and efficient energy conversion technology, offers new insights for the clean treatment of thiophene compounds, which are a significant source of potential pollutants. However, the detailed reaction mechanism of thiophene compounds in the SCWPO process is still unclear. Therefore, the effects of parameters on gasification characteristics and sulfur migration were investigated in the quartz tube reactor during the SCWPO of 2-methylthiophene (2-MT). The results demonstrated that extending the reaction time, increasing the reaction temperature, and reducing the feed concentration favored gaseous product generation. The SCWPO environment with the low equivalent ratio (ER) was favorable for the generation of hydrogen-rich gas. When the conditions were 750 °C, 4 wt%, 15 min, ER = 0.2, the highest H2 yield was 18.59 mol kg−1. With the addition of oxidants, the SCWPO environment promoted the conversion of sulfur from S-2, S-o to S+4, S+6. This conversion reduced the sulfur content in the gas, making it stored in a more environmentally friendly form. Notably, the presence of SOx was not detected during the SCWPO process. Finally, a detailed reaction mechanism for the SCWPO of 2-MT was proposed based on the comprehensive analysis of experimental products.

Enhancing Pb-free inorganic perovskite solar cell using carbon as metal back contact and molybdenum trioxide as hole transport layer

Inorganic Pb-free perovskite solar cells have appeared in recent years as a promising and environmentally friendly technology in photovoltaics. In this study, we conducted a comprehensive simulation investigation using SCAPS-1D software to optimize Pb-free inorganic perovskite solar cells, focusing specifically on the use of RbGeI3 as the absorber material in the FTO/TiO2/RbGeI3/MoO3/C device architecture. The carbon back contact in this configuration stands out for its cost-effectiveness and durability. Our research focused on the influence of various critical parameters, including the thickness of the absorber, electron affinity of ETL and HTL, series, and shunt resistances, back-contact material work functions, and operating temperatures. This achieved a PCE of 29.47 %, FF of 78.22 %, VOC of 1.111 V and JSC of 33.91 mA/cm2. The results indicate that perovskite solar cells using RbGeI3 as an absorber material exhibit improved performance and good thermal stability, underlining the great potential of this material. In addition, the eco-friendly characteristics of these Pb-free inorganic perovskite solar cells hold great promise for advancing the field of clean energy conversion technologies, marking an important step towards sustainable and efficient energy solutions.

Energy Management Considering both Efficiency Optimization and Lifetime Balance of Multi-stack FCS

Abstract With the increase of energy transformation and environmental protection awarenesses, fuel cells, as a clean and efficient energy conversion technology, have been widely adopted in transportation and stationary power supply applications. A single fuel cell has a limited power capability. On the other hand, the multiple fuel cells are combined into a multi-stack fuel cell system (MFCS), which provides a high power output and modular design. However, the energy management of such multi-stack systems faces challenges such as uneven power distribution, inconsistent stack life, and low overall efficiency. Current multi-stack fuel cell control systems often optimize single objectives, either efficiency or lifetime balance produce the optimized energy management strategy. This may not suffice for the overall system benefit. For example, if only efficiency is optimized by energy management, the failure to consider lifetime balance may result in uneven life degradation for each fuel cell, and vice versa. To address the above issues, this paper proposes an energy management strategy for multi-stack fuel cell systems that considers dual objectives, which can simultaneously ensure the optimal co-optimization of the output efficiency and stack life for each stack, thereby improving the overall operating efficiency and lifetime of the system. The effectiveness and practicality of the proposed energy management control strategy were verified on a 60kW dual-stack PEMFC fixed power generation system developed by SeeEx.

Heterointerfaces: Unlocking Superior Capacity and Rapid Mass Transfer Dynamics in Energy Storage Electrodes.

Heterogeneous electrode materials possess abundant heterointerfaces with a localized "space charge effect", which enhances capacity output and accelerates mass/charge transfer dynamics in energy storage devices (ESDs). These promising features open new possibilities for demanding applications such as electric vehicles, grid energy storage, and portable electronics. However, the fundamental principles and working mechanisms that govern heterointerfaces are not yet fully understood, impeding the rational design of electrode materials. In this study, the heterointerface evolution during charging and discharging process as well as the intricate interaction between heterointerfaces and charge/mass transport phenomena, is systematically discussed. Guidelines along with feasible strategies for engineering structural heterointerfaces to address specific challenges encountered in various application scenarios, are also provided. This review offers innovative solutions for the development of heterogeneous electrode materials, enabling more efficient energy storage beyond conventional electrochemistry. Furthermore, it provides fresh insights into the advancement of clean energy conversion and storage technologies. This review contributes to the knowledge and understanding of heterointerfaces, paving the way for the design and optimization of next-generation energy storage materials for a sustainable future.

Nanoscale structural transformations in LaFeO3 oxygen carriers for enhanced reactivity in chemical looping combustion

The push for decarbonization necessitates the development of clean and efficient energy conversion technologies. Among these, the chemical looping platform has emerged as a promising approach, albeit with challenges such as high operating temperatures. This necessitates the design of high-performance chemical looping carriers. In this study, we explore the potential of nanosized oxygen carriers, noted for their high reactivity, for the chemical looping combustion of methane (CH4). LaFeO3, a widely investigated perovskite-type mixed metal oxide known for its effectiveness as an oxygen carrier, is examined. Nanosized LaFeO3 is synthesized by embedding LaFeO3 onto mesoporous silica matrix (LFO-SBA15), and its reactivity is benchmarked against bulk-scale LaFeO3 supported on SiO2 (LFO-SiO2). The nanosized carrier demonstrates a ∼ 1000% improvement in reactivity compared to the bulk carrier. This enhancement is attributed to the formation of a highly reactive cubic phase of LaFeO3 at the nanoscale, in contrast to the orthorhombic phase present in bulk-scale LaFeO3. This finding is supported by density functional theory calculations, which reveal that the cubic phase of LaFeO3 facilitates the formation of oxygen vacancies and lowers the energy barrier for CH4 dissociation. This work highlights the potential of nanosized LaFeO3 for the chemical looping combustion of CH4, providing valuable guidance for the rational design and development of high-performance chemical looping carriers.

Corrosion and Protection of Electrocatalysts toward Advanced Energy Technologies

AbstractHigh‐efficiency electrocatalysts play an important role in clean energy conversion technologies. Generally, electrocatalysts in different environments, including voltage, acid, and alkali electrolytes, are more susceptible to corrosion, which will induce structural and performance changes. Based on the latest achievements in the corrosion and protection of electrocatalysts in advanced energy technologies, this review mainly studies the application of various corrosion strategies to construct superior electrocatalysts, including chemical etching, metal corrosion transformation, and corrosion reconstruction, and their affecting factors are also appraised and summarized. To improve the stability of electrocatalysts, various corrosion inhibition strategies, such as carrier improvement and composition regulation accompanied by structure optimization, are reviewed. In addition, the application of catalyst corrosion in electrochemical energy technologies is examined from the perspective of the structure‐activity‐performance relationship. In the end, this article concludes the perspective and challenges of electrocatalyst corrosion in energy conversion and storage technologies. This article provides insights and directions for designing electrocatalysts with high efficiency and low corrosion, which is beneficial for developing corrosion chemistry for sustainable energy technologies.

Mechanistic Analysis of Urea Electrooxidation Pathways: Key to Rational Catalyst Design.

Urea electrolysis is an emerging approach to treating urea-enriched wastewater and an attractive alternative anodic process to the oxygen evolution reaction (OER) in electrochemical clean energy conversion and storage technologies (e. g., hydrogen production and CO2 electroreduction). While the thermodynamic potential for urea oxidation to dinitrogen is quite low compared to that of the OER, the catalysts reported to date require high overpotentials that far exceed those for the OER. Consequently, there is much room for improvement and rational catalyst design for the urea oxidation reaction (UOR). At the same time, due to the urea molecule having a more complex structure than water, UOR can lead to the formation of various products beyond the commonly assumed N2 and CO2. This concept article will critically assess recent efforts of the research community to decipher the formation mechanisms of UOR products focusing on the systematic analysis of the reaction selectivity. This work aims to analyze the current state of the art and identify existing gaps, providing an outlook for the future design of UOR catalysts with superior activity and selectivity by applying the knowledge of the molecular transformation mechanisms.

Enhancing grid‐connected solar PV systems with a novel three‐phase hybrid multilevel inverter

SummaryThis paper presents a novel three‐phase hybrid multilevel inverter (TPHMLI) designed for grid‐connected solar photovoltaic (SPV) systems. The TPHMLI combines series‐connected bridge topologies of half and full circuits to generate 11 stages of line load voltages, reducing the need for DC sources. It also introduces an improved pulse width modulation (PWM) approach, addressing computational challenges and high‐frequency triggering issues. Practical validation in a laboratory setting demonstrates the MLI's functionality and effectiveness. Furthermore, the advanced MLI topology successfully addresses design issues in grid‐integrated SPV structures, including power quality, efficiency, and reliability. It excels in managing reactive power and fault obstructive capabilities. Extensive simulations using MATLAB/Simulink confirm its superior performance, making it a promising solution for power conditioning units in grid‐connected solar PV systems. This research contributes to clean and sustainable energy conversion technologies, enhancing power quality and cost‐effectiveness, with significant potential for practical applications in the renewable energy sector.

Recent Progress in ZIF‐Derived Carbons for Enhanced Oxygen Reduction Reaction Electrocatalysis

AbstractThe oxygen reduction reaction (ORR) represents a cornerstone for many clean energy conversion technologies such as fuel cells and metal‐air batteries. Nevertheless, the commercialization of these technologies is largely impeded by the slow kinetics of ORR, for which active, durable and cost‐effective ORR catalysts are needed. In recent years, zeolitic imidazolate framework (ZIF) derived carbon materials emerge as a new class of non‐precious metal catalysts (NPMCs) toward ORR, largely benefiting from their high surface area, abundant porosity, tunable chemical/electronic structure, and superior ORR activity which is comparable or even surpasses those state‐of‐the‐art Pt‐based ORR catalysts. This review offers a comprehensive overview of the recent advances in ZIF‐derived carbons for ORR. The synthesis strategies and the key factors affecting the ORR performance of ZIF‐derived carbon materials are discussed. Future research directions and perspectives on exploring ZIF derived carbons as efficient ORR catalysts are highlighted, with a focus on the principles of rationally engineering the coordination structures of active sites.

Innovative application of tomato straw biochar in direct carbon solid oxide fuel cells for power generation

Direct carbon solid oxide fuel cells (DC-SOFCs) demonstrate significant promise in clean energy conversion technology due to their direct utilization of solid carbon, high-temperature operation, and fuel flexibility. Exploring biomass as a fuel for DC-SOFCs is particularly intriguing within this context. Here, we successfully developed the biochar derived from tomato straw and conducted a comprehensive physicochemical characterization to investigate its feasibility and advantages for DC-SOFCs. Electrochemical results revealed that DC-SOFC powered by tomato straw biochar achieved an impressive output of 219 mW cm−2 at 850 °C, surpassing the cell output of 187 mW cm−2 operating on commercial activated carbon. Furthermore, the single cell demonstrated a higher discharge plateau and a longer lifetime of 26.5 h under 50 mA at 850 °C. Consequently, fuel utilization was calculated to be up to 29.7%, which was also superior to that of activated carbon-fueled DC-SOFC, further validating the effectiveness of tomato straw biochar in improving DC-SOFC performance. These outstanding performances were primarily attributed to the unique porous microstructure, naturally existing metal elements, high disorder and large specific surface area of the biochar, which effectively promoted the reverse Boudouard reaction to produce a substantial amount of CO for anode reaction, thus enhancing the DC-SOFC performance and efficiency. These findings underscore the enormous application potential of tomato straw biochar for DC-SOFCs, providing strong support for advancing clean energy technology and achieving carbon neutrality goals.

Metal-organic framework-derived Se-blended ZrO2 with a nitrogen-doped carbon heterostructure for electrocatalytic overall water splitting.

Designing low cost, highly active and efficient non-noble metal bifunctional electrocatalysts with remarkable operational reliability for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is indispensable for large-scale water electrolysis and the development of clean energy conversion technologies. Herein, we decorated a two-dimensional (2D) selenium-blended zirconium dioxide (Se-ZrO2) on the surface of a nitrogen-doped carbon heterostructure (Se-ZrO2@NC), which was derived from Zr-metal-organic frameworks (Zr-MOFs), and loaded it on a stainless-steel mesh electrode. Accordingly, phenomenal electrocatalytic performance was observed for the Se-ZrO2@NC-loaded electrode with a minimum overpotential of 48 mV for the HER and 251 mV for the OER at 10 mA cm-2 current density in acidic and alkaline mediums, respectively. Moreover, a complete cell set up was constructed, where the OER and HER were studied at the anode and cathode, respectively, with a cell potential of 1.58 V to reach a current density of 10 mA cm-2 together with an exciting long-term stability of over 48 h. The developed Se-blended 2D transition metal dioxides on the 2D nitrogen-doped carbon heterostructure extended to a variety of catalytically active materials that would provide highly active and stable electrocatalysts for alkaline water splitting studies.

Emerging Pt-based intermetallic nanoparticles for the oxygen reduction reaction.

The advancement of highly efficient and enduring platinum (Pt)-based electrocatalysts for the oxygen reduction reaction (ORR) is a critical determinant to enable broad utilization of clean energy conversion technologies. Pt-based intermetallic electrocatalysts offer durability and superior ORR activity over their traditional analogues due to their definite stoichiometry, ordered and extended structures, and favourable enthalpy of formation. With the advent in new synthetic methods, Pt-based intermetallic nanoparticles as a new class of advanced electrocatalysts have been studied extensively in recent years. This review discusses the preparation principles, representative preparation methods of Pt-based intermetallics and their applications in the ORR. Our review is focused on L10 Pt-based intermetallics which have gained tremendous interest recently due to their larger surface strain and enhanced M(3d)-Pt(5d) orbital coupling, particularly in the crystallographic c-axis direction. Additionally, we discuss future research directions to further improve the efficiency of Pt-based intermetallic electrocatalysts with the intention of stimulating increased research ventures in this domain.

Electrosynthesis of ruthenium nanocluster incorporated nickel diselenide for efficient overall water splitting

Design of effective catalyst activation strategies that enable efficient electrocatalytic activity towards overall water splitting is necessary for the development of clean energy conversion technologies.

Electrospun Fuel Cell Electrodes and Their Behavior Under Hydrogen/Air Start-up/Shut-Down Conditions

Affordable and clean energy is one of the 17 sustainable development goals proposed by the United Nations in 2015. [1] In this context, polymer electrolyte membrane fuel cells (PEMFCs) are a promising renewable and clean energy conversion technology. The large implementation of PEMFCs, however, is hindered by high loading of very costly and scarce platinum group metals (PGM) and insufficient long-term durability. Most of the cathode catalysts are suffering from hydrogen/air start-up/shut-down (SUSD) conditions. [2, 3] Generally, the performance of the PEMFC is controlled by the utilization of the catalytically active sites and the mass transport properties within the porous catalyst layers (CL) in particular operating at high current density. New strategies in the design of functional porous catalyst layers are needed to overcome these challenges. As a very promising strategy, nanometer-sized fibers prepared by electrospinning can be used as a backbone to improve the utilization and accessibility of catalytically active sites by maintaining the PGM loading. [4, 5]In this work, a nozzle-free electrospinning machine by Elmarco S.R.O. (Liberec, Czech Republic) was employed to design and nano-engineer advanced catalyst layers with improved catalytic as well as mass transport properties. Thereby, several highly homogeneous catalyst layers deposited on gas diffusion layer with controlled platinum loading of up to 0.1 mg/cm2 were prepared and characterized by scanning electron microscope (SEM) and micro X-ray fluorescence spectroscopy (μ-XRF). The structural information such as morphology and chemical distribution was correlated with the electrochemical data obtained from the single cell measurements in a fuel cell test station. Additionally, the durability of the as-prepared nanofiber-based catalyst layers was studied under real hydrogen/air SUSD conditions.Our results show the impact of different nanostructured catalyst layers prepared by electrospinning process on the long-term performance of the PEMFC. Here, we will present the great advantages of the electrospun catalyst layers over the classical catalyst layers prepared by decal transfer process.

Metal-Organic Framework (MOF)-Based Clean Energy Conversion: Recent Advances in Unlocking its Underlying Mechanisms.

Carbon neutrality is an important goal for humanity . As an eco-friendly technology, electrocatalytic clean energy conversion technology has emerged in the 21st century. Currently, metal-organic framework (MOF)-based electrocatalysis, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), carbon dioxide reduction reaction (CO2 RR), nitrogen reduction reaction (NRR), are the mainstream energy catalytic reactions, which are driven by electrocatalysis. In this paper, the current advanced characterizations for the analysesof MOF-based electrocatalytic energy reactions have beendescribed in details, such as density function theory (DFT), machine learning, operando/in situ characterization, which provide in-depth analyses of the reaction mechanisms related to the above reactions reported in the past years. The practical applications that have been developed for some of the responses that are of application values, such as fuel cells, metal-air batteries, and water splitting have also been demonstrated. This paper aims to maximize the potential of MOF-based electrocatalysts in the field of energy catalysis, and to shed light on the development of current intense energy situations.