Clean Energy Conversion Research Articles

Highly conductive dodecaborate/MXene composites for high performance supercapacitors

With the increasingly prominent energy and environmental issues, the supercapacitors, as a highly efficient and clean energy conversion and storage devices, meet the requirements well. However, it is still a challenge to enhance the capacitance and energy density of supercapacitors. A novel and highly conductive dodecaborate/MXene composites have been designed for high performance supercapacitors. The surface charge property of MXene was modified by a simple ultrasonic treatment with ammonium ion, and the dodecaborate ion can be inserted into the inner surface of MXene by electrostatic adsorption. Due to the unique icosahedral cage conjugate structure formed by the B-B bond and the highly delocalized three-dimensional π bond structure of the electrons, the negative charge is delocalied on the whole dodecaborate ion, which reduces the ability to bind to cations. Therefore, the cations can move easily, and the dodecaborate can act as a “lubricant” for ion diffusion between the MXene layers, which significantly improves the ion transfer rate of supercapacitors. The dodecaborate/MXene composites can achieve an extremely high specific capacitance of 366 F.g-1 at a scan rate of 2 mV.s-1, which is more than eight times higher than that of MXene (43 F1-) at the same scan rate. Our finding provides a novel route on the fabrication of the high performance supercapacitors.

Editorial: Electrocatalysis ‐ From Batteries to Clean Energy Conversion

Editorial: Electrocatalysis ‐ From Batteries to Clean Energy Conversion

Modelling and optimisation of a hybrid PV-wind turbine-pumped hydro storage energy system for mini-grid application in coastline communities

This study proposes a clean, reliable and affordable hybrid energy conversion technology that is based on sunlight and wind, with a hydro based energy storage system. The proposed system comprises Photovoltaic arrays, wind turbine (WT) and Pumped Hydro Energy Storage (PHES). The study was focused on satisfying energy demand of a typical coastline community, Patani (Lat. 5.23° N and Long. 6.17° E) – a Local Government Area (LGA). Genetic algorithm was adopted to optimise the PHES of the proposed hybrid plant to minimise the difference between energy demand and energy generated. Economic models were developed to ascertain the economic feasibility of the hybrid plant. High fidelity software (HOMER®, MATLAB® and MS Excel® spreadsheet) were utilised for the analysis and optimisation. The peak rated power of PV and WT required to satisfy the energy demand of the LGA are 217 kWp and 226050 kW, respectively. The minimum storage capacity of the PHES was estimated at about 3,930,615 kWh, with the upper reservoir volume of 43170.06 m3. The value of 0.27 $/kWh was obtained for the Levelised Cost of Energy (LCOE); while the loss of load probability of the proposed energy system was estimated at 0.1086. The proposed energy system supports the Sustainable Development Goal 7 – affordable and clean energy, with climate change mitigation potential.

Honeycomb-like 3D N-, P-codoped porous carbon anchored with ultrasmall Fe2P nanocrystals for efficient Zn-air battery

Fabrication of transition metal phosphides/carbon hybrids as electrocatalysts for oxygen reduction reaction (ORR) has great significance for developing clean energy conversion and storage devices based on earth abundant elements. In this work, we prepared 3D N,P-codoped porous carbon supported with ultrasmall Fe2P nanoparticles (Fe2P/NPC) as high-efficient ORR catalyst by a simple grinding-calcination strategy. As the pore-forming agent, ZnO nanospheres can be in-situ eliminated and generate abundant porous structures which are beneficial to mass transfer. Meanwhile, the large BET surface area (1288 m2 g−1) and pore volume (1.23 cm3 g−1) of Fe2P/NPC can provide more contact active centres for ORR. In alkaline solution, Fe2P/NPC performs excellent ORR activity with the positive onset potential (0.997 V) and half-wave potential (0.872 V), which are more positive than those of the commercial Pt/C (0.977 and 0.812 V). In addition, Fe2P/NPC can be used as air cathode catalyst in a Zn-air battery whose open circuit voltage (1.469 V) is larger than that of the commercial Pt/C (1.332 V) based one. This work provides new strategy to prepare transition metal phosphides/carbon hybrids for electrocatalysis and clean energy conversion systems.

Gold-Supported Nanostructured NiFeCoPr Hydroxide as a High-Performance Supercapacitor Electrode and Electrocatalyst toward the Oxygen Evolution Reaction

Facile and high-performance electrode materials are crucial for the conversion and storage of clean energy. A gold-supported nanostructured NiFeCoPr hydroxide is synthesized by directly electrodepositing praseodymium-doped nickel-cobalt-iron hydroxide onto a gold-deposited nickel foam (NF) substrate. The resultant monolithic NiFeCoPrO-Au/NF electrode exhibits a high specific capacitance (1792 F g-1 at a current density of 10 A g-1), excellent rate capability (1445 F g-1 at a current density of 70 A g-1), and eminent capacitance retention (99.5% after 30 000 cycles) in 3 M KOH electrolyte. When used as an oxygen evolution electrocatalyst, NiFeCoPrO-Au/NF shows high catalytic activity for the oxygen evolution reaction with a small Tafel slope of 28 mV dec-1 in 1 M KOH electrolyte and excellent stability over 10 h. These characteristics demonstrate the enormous potential of the NiFeCoPrO-Au/NF electrode for applications in electrocatalysis and supercapacitors.

Metallic Co9S8 Coupled Hollow N‐Doped Carbon Sphere with Synergistic Interface Structure for Efficient Electricity Generation in Microbial Fuel Cells

AbstractThe high cost, low abundance and poor durability of precious metal catalysts greatly hinder the practical applications of microbial fuel cells (MFCs) for bioremediation and bioelectricity generation. It is imperative to develop highly efficient and robust noble metal‐free catalysts for the high power density of MFCs. In this work, we present a scalable and cost‐effective strategy to synthesize Co9S8 nanoparticles coupled with nitrogen‐doped hollow carbon sphere (NHCS), which subtly constructs synergistic interface structures that expose plentiful active sites and afford high conductive channel for charge transfer. The as‐obtained porous Co9S8/NHCS exhibits excellent catalytic activity, and superior stability as well as methanol tolerance during oxygen reduction reaction (ORR) process in both alkaline and neutral environment. The MFC device equipped with Co9S8/NHCS as air‐cathode achieves a remarkable power density of 704±22 mW m−2 and outstanding chemical oxygen demand (COD) removal rate of 96.28 %±0.50 %, which is even superior to the performance of commercial Pt/C catalyst. The favorable results provide a new concept to design and explore porous noble metal‐free electrocatalysts for clean and sustainable energy conversion.

Facile synthesis of nickel cobalt selenide hollow nanospheres as efficient bifunctional electrocatalyst for rechargeable Zn-air battery

Designing high active, low cost and bifunctional electrocatalysts is urgent for developing clean energy storage and conversion systems. Transition metal selenides exhibit optimal electronic conductivity and tunable physicochemical properties, which endow them with potential for efficient electrocatalysts to facilitate the oxygen reduction and oxygen evolution reactions (ORR and OER). Herein, hollow NixCo0.85-xSe nanospheres were synthesized using a facile polyol based solution chemical method. The NixCo0.85-xSe exhibits an onset overpotential of 0.89 V for ORR, and an overpotential of 305 mV to achieve 10 mA cm−2 for OER. Moreover, the NixCo0.85-xSe based Zn-air battery displays remarkable specific capacity and durability. Such superior catalytic performances can be attributed to the synergistic effect, large specific surface area and enhanced electron transfer rate. This approach provides a new way to design highly efficient bifunctional electrocatalysts for electrochemical energy storage and utilization.

Mn Nanoparticles Encapsulated within Mesoporous Helical N‐Doped Carbon Nanotubes as Highly Active Air Cathode for Zinc–Air Batteries

AbstractThe practical application of clean energy conversion and storage technologies, such as fuel cells and metal–air batteries, have been significantly impeded by the high cost and scarcity of precious metal catalysts used for the oxygen reduction reaction (ORR). Transitional metal/carbon compounds are a promising alternative to precious metal catalysts for the ORR. Herein, Mn nanoparticles encapsulated within mesoporous helical N‐doped carbon nanotubes (Mn@HNCNTs) are developed as highly active ORR catalysts. In terms of the onset potential and half‐wave potential for ORR, the optimized Mn@HNCNTs exhibit an excellent ORR performance, which is comparable to Pt/C. When the Mn@HNCNTs are assembled as air cathodes, with zinc foil as the anode in primary zinc–air cells, the obtained cell delivers a higher cell voltage and capacity than the zinc–air cell using Pt/C as the air cathode, as well as many reported cells using TM/CNT‐based air cathodes. The electrocatalytic performance in the zinc–air cell demonstrates that Mn@HNCNTs have great potential for use as ORR catalysts in metal–air batteries.

Recent Progress in Electrochemiluminescence Sensing and Imaging.

Life science and energy conversion have been becoming the two major themes in 21st century considering the increasing awareness of disease prevention and overuse of fossil fuels. Therefore, how to understand the evolution mechanisms of single cells and the fundamental pathways of clean energy conversion have become significant matters of utmost urgency. Electrochemical measurement is a powerful analytical method that has been used for a wide range of applications including detecting faint bioelectricity and evaluating novel electrocatalysts. Nevertheless, conventional electrochemical techniques suffer from limited sensitivity due to the interference of charging/discharging current and side reactions. As a branch of electrochemical technologies, however, electrochemiluminescence (ECL) possesses high sensitivity and broad dynamic range by the transformation of input electrical signal into optical readout, which differs from most other electrochemical techniques. In fact, ECL relies on the generation of elec...

Operation optimization and income distribution model of park integrated energy system with power-to-gas technology and energy storage

Power-to-gas (P2G) technology is considered as a new approach for clean energy consumption and energy conversion. However, because this technology must be combined with other energy systems to build a stable energy system, a reasonable income distribution method is necessary to guarantee this integration. Firstly, the operation optimization model of the park integrated energy system (PIES) and park independent energy system (PINES) with P2G are constructed for the first stage optimization, with the objective of maximizing net income. Secondly, the energy system performance evaluation indicators are developed to assess the system quantitatively in terms of the economic and environmental aspects. Thereafter, the income distribution models based on Shapley value and the improved Shapley value with operational risk factor are created, and the total income is optimally distributed at the second stage based on the first-stage optimization results. Finally, an industrial park in a province of China is selected for case analysis. The results show that (1) PIES can complement different systems, integrate the demands in heat, electricity, and gas, while realizing the electricity-gas-heat/electricity conversion and heat-electricity complementarity. (2) Income distribution using an improved Shapely value method is proposed, it overcomes the one-sidedness of transaction volume and lack of differences among participants, reflects the actual operational risk and the degree of contribution of participants to the whole system, and promotes the incentives of cooperation. (3) Based on the improved income distribution model, the income of the PS, P2G, and HS are redistributed. The income of P2G increased by ¥7,450, which reflects the important collaborative value of P2G. The willingness of system cooperation increased by 742.392%. Therefore, the proposed operation optimization and income distribution model can enhance the incentives of participants want to cooperate under the premise of ensuring the maximum net income of the PIES. Moreover, it can be used as reference for the formulation of an optimal operation plan and income distribution of the complex energy system and it can provide a way to promote clean energy production. • The role of P2G as a new energy conversion way is studied. • The two-stage optimization model is constructed. • The first stage is operational optimization. • The second stage is income distribution. • The improved Shapley value method is applied in park integrated energy system.

Integration of Solid Oxide Fuel Cells into oil and gas operations: needs, opportunities, and challenges

Abstract The oil and gas industry generates a significant amount of harmful greenhouse gasses that cause irreversible environmental impacts. The level of impact is worsened by the world’s utter dependence on fossil fuels as its primary source of energy, as well as the low efficiency of energy plants processing such fuels. Utilizing a renewable energy source instead of oil and gas is the ultimate long-term solution to this problem. However, there will be a transitional phase from fossil fuels-based economy to a projected economy based on cleaner hydrocarbon resources, and natural gas will play a significant role in such a transition. The primary purpose of this review study is to develop a fundamental understanding to enhance operational efficiency and to reduce emissions associated with oil and gas operations by integrating a clean energy conversion system - Solid Oxide Fuel Cell (SOFC). SOFCs have been proven to be highly efficient electrochemical devices that directly convert chemical energy to electricity with the potential to improve system efficiencies. This will, in turn significantly reduce emissions in oil and gas operations. Enabling an effective integration, smarter utilization of SOFC systems at different scales can lead to overall system efficiency improvements. This review study will highlight the ongoing integration of SOFC in different areas and then select the most suitable aspect of such integration for natural gas processing plants. Areas of improvement could include the SOFC integration with steam and power systems, integration with flare system, or even combined with PV, to provide the required energy throughout the day. Besides, this study will highlight the challenges related to the usage of SOFCs in gas plants, primarily financial-related challenges but also performance challenges. The study further discusses recent developments in this field as well as future work needed to enhance and encourage the integration of SOFC systems in energy-intensive and highly pollutant oil and gas operations, to convert them into sustainable and greener processes.

Morphology engineering of 3D nanostructure MMNS as bifunctional electrocatalysts towards high-efficient overall water splitting

It is highly desired but still a significant challenge to construct preeminent non-noble metal bifunctional electrocatalysts for large-scale electricity-to-hydrogen generation. In the paper, four novel morphologies of MMNS including epiphyllum-like MMNS-NFs1, ice flower-like NFs2, grape-like NRs1, and nanorod NRs2 were successfully achieved via a facile two-step process by adjusting C2H5NS/CO(NH2)2 M ratio and/or H2O/ethanol solvent composition. Electrochemical activities of as-prepared four samples were systematically studied, while 3D nanorods core-shell nanostructure MMNS-NRs2 exhibits high-efficient electrocatalytic performance towards HER (158 mV @ 10 mA cm−2) and OER (134 mV @ 40 mA cm−2). What's more, when MMNS-NRs2 was served as the cathode and anode for overall water splitting in 1.0 M KOH, only a low cell voltage of 1.52 V and 1.60 V were required for MMNS-NRs2//MMNS-NRs2 electrode pairing to reach the current density 20 mA cm−2 and 100 mA cm−2, respectively. MMNS-NRs2//MMNS-NRs2 also performs an outstanding long-term durability at least 16 h without obvious deactivation. The reason for outstanding electrochemical properties and stability of MMNS-NRs2 was owing to the fact that unique core-shell nanostructure can facilitate electron/ion transfer and mass transport, 3D nanosheets endow more active sites and higher electron transport rate and the synergistic effect of Mo and Mn composition. This work provides a well-designed structure and development for morphology engineering to construct high-performance material for clean energy conversion technologies.

Nanosized Composite Electrodes Based on Polyaniline/Carbon Nanotubes Towards Methanol Oxidation

Background: Direct methanol fuel cells as a clean and efficient energy conversion method for portable electronic devices and electric vehicles are a very popular subject in science and engineering. Up to now, the most effective anode electrode materials for direct methanol fuel cells are Pt- Ru, used mainly as bimetallic catalysts dispersed on a highly active conductive support, such as conducting polymer, carbon-based catalysts, or a composite matrix composed of both. Objective: The main objective is to decrease the amount of precious metal-Pt required for financial considerations and to overcome the insufficient oxidation reactions’ rate of the fuel, which lead to the inevitable, naturally high, overpotential in fuel cell applications. Thereby, current research addresses the preparation of Pt, Pt-Ru, Pt-Ru-Pd and Pt-Ru-Mo metal nanoparticles modified by both polyaniline-multi-wall carbon nanotubes and polianiline-functionalized multi-wall carbon nanotubes composites and their activity in the methanol electro-oxidation. Methods: All of the composite surfaces were successfully prepared using electrochemical methodologies. A Citrate method was used for the preparation of metal nanoparticles. A comparative study was conducted on each stage of the investigation. The modified surfaces were characterized and analyzed by SEM, EDX, XRD, Raman, and TEM. Results: According to the spectroscopic measurements, all particles synthesized were detected as nanoscale. Binary and ternary catalysts supported on composite surfaces had higher activity and efficiency when compared to monometallic systems. Conclusion: The fabricated electrodes showed comparable catalytic activity, long-term stability, and productivity towards direct methanol fuel cell applications in acidic media.

Morphological and Structural Evolution of Co3O4 Nanoparticles Revealed by in Situ Electrochemical Transmission Electron Microscopy during Electrocatalytic Water Oxidation.

Unveiling the mechanism of electrocatalytic processes is fundamental for the search of more efficient and stable electrode materials for clean energy conversion devices. Although several in situ techniques are now available to track structural changes during electrocatalysis, especially of water oxidation, a direct observation, in real space, of morphological changes of nanostructured electrocatalysts is missing. Herein, we implement an in situ electrochemical Transmission Electron Microscopy (in situ EC-TEM) methodology for studying electrocatalysts of the oxygen evolution reaction (OER) during operation, by using model cobalt oxide Co3O4 nanoparticles. The observation conditions were optimized to mimic standard electrochemistry experiments in a regular electrochemical cell, allowing cyclic voltammetry and chronopotentiometry to be performed in similar conditions in situ and ex situ. This in situ EC-TEM method enables us to observe the chemical, morphological, and structural evolutions occurring in the initial nanoparticle-based electrode exposed to different aqueous electrolytes and under OER conditions. The results show that surface amorphization occurs, yielding a nanometric cobalt (oxyhydr)oxide-like phase during OER. This process is irreversible and occurs to an extent that has not been described before. Furthermore, we show that the pH and counterions of the electrolytes impact this restructuration, shedding light on the materials properties in neutral phosphate electrolytes. In addition to the structural changes followed in situ during the electrochemical measurements, this study demonstrates that it is possible to rely on in situ electrochemical TEM to reveal processes in electrocatalysts while preserving a good correlation with ex situ regular electrochemistry.

Special Issue: “Thin Films for Energy Harvesting, Conversion, and Storage”

Efficient clean energy harvesting, conversion, and storage technologies are of immense importance for the sustainable development of human society. To this end, scientists have made significant advances in recent years regarding new materials and devices for improving the energy conversion efficiency for photovoltaics, thermoelectric generation, photoelectrochemical/electrolytic hydrogen generation, and rechargeable metal ion batteries. The aim of this Special Issue is to provide a platform for research scientists and engineers in these areas to demonstrate and exchange their latest research findings. This thematic topic undoubtedly represents an extremely important technological direction, covering materials processing, characterization, simulation, and performance evaluation of thin films used in energy harvesting, conversion, and storage.

Two-dimensional Cobalt Oxy-hydrate Sulfide Nanosheets with Modified t2g Orbital State of CoO6–x Octahedron for Efficient Overall Water Splitting

Searching for low-cost, scalable, highlly active electrocatalysts for clean energy conversion has become the main challenge presently. A two-dimensional cobalt oxy-hydrate sulfide (CoO(OH)1–xSx) na...

MOF-derived Co9S8/MoS2 embedded in tri-doped carbon hybrids for efficient electrocatalytic hydrogen evolution

Abstract Metal–organic framework (MOF) derived hybrid materials have been developed as an efficient non-noble-metal electrocatalysts for clean energy conversion systems. In this work, a Co-based MOF containing nitrogen and oxygen heteroatoms (Co-NOMOF) mixed with the thiomolybdate [Mo3S13]2− nanoclusters was used to prepare the N, S, O-doped carbon encapsulating Co9S8 and MoS2 (Co9S8/MoS2@NSOC) nanocomposite by one-step pyrolysis. The Co9S8/MoS2@NSOC nanocomposite exhibited remarkable catalytic performance for hydrogen evolution reaction (HER) with overpotential of 194 and 233 mV in 1 M KOH and 0.5 M H2SO4 solution under 10 mA cm−2, respectively, which was ascribed to the multiheteroatom-doped hierarchical porous carbon matrix and the synergistic effect of intrinsic activity of Co9S8 and MoS2. This work provides new opportunity for developing highly efficient non-precious metal electrochemical catalysts.

Nitrogen-doped hollow carbon spheres as highly effective multifunctional electrocatalysts for fuel cells, Zn–air batteries, and water-splitting electrolyzers

Clean energy conversion technologies require low-cost multifunctional catalysts. In this work, nitrogen-doped hollow carbon spheres with nanoporous shells (NHCS–W) are prepared by using the ionic liquid 1-butyl-3-methylimidazolium chloride as a source of both carbon and nitrogen. A systematic investigation of the electrocatalytic performance and durability of NHCS–W reveals excellent performance and high stabilities for the oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction in alkaline electrolytes. This multifunctionality facilitates promising practical applicability for NHCS–W. An alkaline exchange membrane fuel cell (AEMFC) with NHCS–W as the cathode electrocatalyst has a peak power density of 109 mW cm−2, which is 7 mW cm−2 higher than that of an AEMFC with Pt/C (20%) as the cathode electrocatalyst. By using NHCS–W as an air electrode, two rechargeable Zn–air batteries in series can power a 5 mm red light-emitting diode (~2.2 V). Moreover, a cell voltage of only 1.61 V is needed to achieve a current density of 10 mA cm−2 in a water-splitting electrolyzer employing NHCS–W as both the cathode and anode catalysts. This work reveals the potential of ionic liquid precursors for constructing nitrogen-doped carbon-based materials for a wide variety of electrocatalytic applications.

Surface/interface engineering of noble-metals and transition metal-based compounds for electrocatalytic applications

Surface/interface engineering plays an important role in improving the performance and economizing the cost and usage of electrocatalysts. In recent years, substantial progress has been achieved in designing and developing highly active electrocatalysts with the deepening understanding of surface and interface enhanced mechanism. In this review, recent development about optimizing the surface and interfacial structure in promoting the electrocatalytic activity of noble-metals and transition metal compounds is presented and the chemical enhancements are also described in detail. The relationship between the surface/interface structures (both atomic and electronic configuration) and the electrochemical behaviors has been discussed. Finally, personal perspectives have been proposed, highlighting the challenges and opportunities for future development in tuning the surface/interface active sites of electrocatalysts. We believe that this timely review will be beneficial to the construction of highly active and durable electrode materials through optimizing surface atomic arrangement and interfacial interaction, which can largely promote the development of next-generation clean energy conversion technologies.

Controlled Synthesis of CuCo2 S4 @Ni(OH)2 Hybrid Nanorod Arrays for Water Splitting at an Ultralow Cell Voltage of 1.47 V.

Developing environmentally friendly and highly active water splitting catalysts would be of great significance for clean energy conversion and utilization processes. Heterogeneous CuCo2 S4 @Ni(OH)2 nanorod arrays with abundant oxygen vacancy firstly have been designed through a controllable hydrothermal and electrodeposition method. The synergies and open structures of the particular hierarchical structure together with the abundant oxygen vacancies offer more surface reactive centers, which can promote the electron transfer rate and reduce the activation energy of intermediate species. The CuCo2 S4 @Ni(OH)2 -20 min nanorod arrays are considered as an excellent and robust electrocatalyst for the proton reduction under an alkaline condition with an extraordinary low overpotential of 117 mV at 10 mA cm-2 . The CuCo2 S4 @Ni(OH)2 -20 min heterostructures electrode is also stable and robust for the water oxidation reaction, needing an overpotential of only 250 mV to obtain 100 mA cm-2 . Therefore, an alkaline electrolyzer was designed using CuCo2 S4 @Ni(OH)2 -20 min nanorod arrays as bifunctional electrocatalyst, which can complete overall water splitting at a cell voltage of 1.47 V with 10 mA cm-2 , suggesting a promising combination of the same material for efficient overall water splitting device. The cell voltage of 1.47 V, to our knowledge, is among the lowest values of the published support catalysts for electrocatalytic water splitting up to now.