Renewable Energy Conversion Research Articles

Porous Ni Electrodes for Hydrogen Production from Water Electrolysis

Hydrogen has been seen as one of the most valuable options regarding renewable energy storage and conversion. However, its production is still mostly based on fossil fuels, in part because of the high cost of alternative production routes, as is the case of water electrolysis for example. This fact is explained by the energy consumed during the process of hydrogen evolution from water. Nevertheless, the research on water electrolysis is justifiable by the advantages that the process offers, as high produced hydrogen purity, possible association with other renewable energy sources such as solar, hydro and wind power generation, no CO2 emissions during the evolution, simplicity of the process, as so many others. With the purpose of increasing the hydrogen-producing device (electrolysers) performance, great scientific efforts have been directed to the electrodes base materials and their surface technology. In this way, the present work propose powder metallurgy based processes as production routes of nickel porous electrodes, i.e., relatively low cost and high active superficial area electrodes for hydrogen production.

The thermophysical properties of a promising composite adsorbent based on multi-wall carbon nanotubes for heat storage

AbstractThe use of energy from alternative energy sources as well as the use of waste heat are key elements of an efficient energetics. Adsorption heat storage is a technology that allows solving such problems. For the successful operation of an adsorption heat accumulator, it is necessary to analyze the thermophysical characteristics of the system under the conditions of the operating cycle: heat transfer coefficient adsorbent-metal (α2), overall (U) and global (UA) heat transfer coefficients of heat exchanger. Multi-walled carbon nanotube (MWCNT) composites are very promising for adsorption-based renewable energy storage and conversion technologies. In this work at the stage of heat release, α2 was measured by the large pressure jump (LPJ) method, at the stage of heat storage by large temperature jump method (LTJ), which made it possible to obtain thermophysical characteristics that corresponded to the implementation of the real working cycle as much as possible. The heat transfer coefficients for a pair of adsorbent LiCl/MWCNT—methanol are measured for the first time under the conditions of a daily heat storage cycle both at the sorption stage (α2 = 190 W/m2K) and at the desorption stage (α2 = 170 W/m2K).

Online Determination of Grid Impedance Spectrum through Pseudo-Random Excitation of a Pulse Width Modulator

The last decade has seen a dramatic rise in renewable energy converters connected to the grid, consisting mostly of intermittent distributed generators on the medium or low voltage grid. Due to this evolution in energy transmission, improved monitoring and control of the distribution grid is becoming mandatory in order to efficiently integrate the new power sources and guarantee power quality, efficiency and reliability. Our paper describes a reliable and precise power grid impedance estimation method using an innovative scheme to control the Pulse Width Modulator’s pulse pattern on the inverters, in order to inject broad spectrum identification patterns. The generated harmonics and inter-harmonics will allow the online computation of the complete spectrum of the grid impedance at the Point of Common Coupling during normal operation. Simulations in typical grid situations verify that the proposed algorithm is robust to a realistic environment and can be used for automated feedback control.

High-entropy oxides for energy-related electrocatalysis

Electrocatalysis plays a crucial role in the conversion and storage of renewable energy, offering significant potential for addressing the energy crisis and environmental concerns. High-entropy oxides (HEOs), a class of emerging functional materials, have gained increasing attention in electrocatalysis due to their stable crystal structure, exceptional geometric compatibility, unique electronic balance factors, and abundant active sites. In this comprehensive review, we present recent advancements in utilizing HEOs as catalysts for various energy-based electrocatalytic reactions. We begin with an overview of HEOs that includes definitions, fundamental properties, and theoretical investigations. Subsequently, we describe different synthetic methods for HEOs while highlighting two newly-developed techniques. Furthermore, we extensively discuss recent developments in HEO-based electrocatalysts with diverse crystal structures such as rock-salt-type, rutile-type, spinel-type, perovskite-type, and other specially-structured HEOs. Special emphasis is placed on designed strategies aimed at enhancing performance and exploring correlations between structure/ composition and electrocatalytic performance. Finally, we provide concluding remarks along with perspectives on future opportunities in this exciting field.

Energy response of a mono-axis tracked solar thermal collector with vacuum tubes

. Looking towards a sustainable future, Transilvania University of Brasov develops many projects on diverse renewable energy conversion systems; this paper presents a solar tracked solar thermal collector (STC) system, designed for a future implementation on Transilvania University campus. The specific requirement is that the STC system has to be configured to keep a zero energy response during the summer holydays (when the energy consumption is null). The proposed solution describes a mono-axial solar tracking system designed to perform an annual step wise tracking program to capture the most of the available solar energy using a solar thermal collector (STC) with vacuum tubes. The tracking program represents an optimised step tracking law developed in dependence with the diurnal movement of the sun. Numerical simulations are done for one year interval, for Brasov Romania geographic site, to evaluate the daily variations of: the pseudo-equatorial solar angles (γ, β); the pseudo-equatorial tracking angles (γ*, β*); the incidence angle; the available beam solar radiation (B) and the beam received solar radiation by the STC system (B*). The energy response of the tracked STC, for Brasov, Romania, is evaluated considering both clear sky and cloudy sky conditions, while neglecting the diffuse radiation effect.

Catalysis with Two-Dimensional Metal-Organic Frameworks: Synthesis, Characterization, and Modulation.

The demand for the exploration of highly active and durable electro/photocatalysts for renewable energy conversion has experienced a significant surge in recent years. Metal-organic frameworks (MOFs), by virtue of their high porosity, large surface area, and modifiable metal centers and ligands, have gained tremendous attention and demonstrated promising prospects in electro/photocatalytic energy conversion. However, the small pore sizes and limited active sites of 3D bulk MOFs hinder their wide applications. Developing 2D MOFs with tailored thickness and large aspect ratio has emerged as an effective approach to meet these challenges, offering a high density of exposed active sites, better mechanical stability, better assembly flexibility, and shorter charge and photoexcited state transfer distances compared to 3D bulk MOFs. In this review, synthesis methods for the most up-to-date 2D MOFs are first overviewed, highlighting their respective advantages and disadvantages. Subsequently, a systematic analysis is conducted on the identification and electronic structure modulation of catalytic active sites in 2D MOFs and their applications in renewable energy conversion, including electrocatalysis and photocatalysis (electro/photocatalysis). Lastly, the current challenges and future development of 2D MOFs toward highly efficient and practical electro/photocatalysis are proposed.

Recent Progress in the Application of Ion Beam Technology in the Modification and Fabrication of Nanostructured Energy Materials.

The development of green, renewable energy conversion and storage systems is an urgent task to address the energy crisis and environmental issues in the future. To achieve high performance, stable, and safe operation of energy conversion and storage systems, energy materials need to be modified and fabricated through rationalization. Among various modification and fabrication strategies, ion beam technology has been widely used to introduce various defects/dopants into energy materials and fabricate various nanostructures, where the structure, composition, and property of prefabricated materials can be further accurately tailored to achieve better performance. In this paper, we review the recent progress in the application of ion beam technology in material modification and fabrication, focusing on nanostructured energy materials for energy conversion and storage including photo- (electro-) water splitting, batteries (solar cells, fuel cells, and metal-ion batteries), supercapacitors, thermoelectrics, and hydrogen storage. This review first provides a brief basic overview of ion beam technology and describes the classification and technological advantages of ion beam technology in the modification and fabrication of materials. Then, modification of energy materials by ion beams is reviewed mainly concerning doping and defect introduction. Fabrication of energy materials is also discussed mainly in terms of heterojunctions, nanoparticles, nanocavities, and other nanostructures. In particular, we emphasize the advantages of ion beam technology in improving the performance of energy materials. Finally, we point out our understanding of challenges and future perspectives in applying ion beam technology for the modification and fabrication of energy materials.

Effect of tunable composition-shape of bio-inspired Pt NPs electrocatalyst in direct methanol fuel cell: Process optimization and kinetic studies

Highly efficient bio-inspired platinum nanoparticles (Pt NPs) as an electrocatalyst with superior intrinsic kinetics and high performance for methanol oxidation reaction (MOR) derived from green synthesis of bio-waste utilization is of great interest. The bio-inspired Pt NPs were examined for their kinetic parameters in terms of the Tafel plot, exchange current, square root of the scan rate, methanol diffusion coefficient, activation energy (Ea), and factors influencing current density. Bio-inspired Pt NPs exhibit a fast kinetic reaction with a low Tafel value of 179 mV dec−1 and exchange current, α = 0.33, compared to commercial Pt black (233 mV dec−1, α = 0.25). The bio-inspired Pt NPs display low activation energy, Ea, as the potential increases, indicating improved intrinsic kinetics, and the MOR catalyzed by bio-Pt NPs was discovered to be a diffusion-controlled process. The parametric effect of bio-inspired Pt NPs concentration has a crucial influence on the anisotropic morphological structure and interconnection to the current density (mA mg−1) of MOR. Central Composite Design (CCD) was applied for RSM-based modeling and analyzing the parameter effects, including bio-inspired Pt NPs concentration, methanol concentration, and electrocatalyst loading to optimize the current density. The optimized current density produced by bio-inspired Pt NPs was 640.11 mA mgPt−1 at ideal conditions of 1.5 mM bio-Pt NPs, 1.05 M CH3OH, and 2.14 mg. Ultimately, the passive DMFC single-cell powered by bio-inspired Pt NPs generates power density with Pmax of 5.70, 6.67, and 8.28 mW cm−2 at 25, 80, and 100 °C. Thus, bio-inspired Pt NPs derived from green synthesis pathways and biomass-mediated extract have been proven to be viable and sustainable anode electrocatalysts for utilization in the energy conversion of renewable energy with outstanding performance.

Questing for High-Performance Electrocatalysts for Oxygen Evolution Reaction: Importance of Chemical Complexity, Active Phase, and Surface-Adsorbed Species.

Rational design of advanced electrocatalysts for oxygen evolution reaction (OER) is of vital importance for the development of sustainable energy. Entropy engineering is emerging as a promising approach for the design of efficient OER electrocatalysts. However, other multi-anion/cation electrocatalysts with compositional complexity, particularly the medium-entropy and other non-equimolar cation/anion complex electrocatalysts, have not received noteworthy attention. In this perspective, we review and highlight the importance of compositionally complex catalysts and propose a concept of chemical complexity to correlate the OER catalytic activity with the contributions from the pairwise cation-anion interactions. Then, we offer a new view on the active catalytic sites being the hydroxylated reacting interface in an alkaline solution. Further, we argue that the common discrepancies between computationally predicted OER activities and experimental results stem from lack of considerations of surface-adsorbed species in modeling the active catalytic phases or sites. This perspective would facilitate achieving a renewed and profound understanding of the OER mechanism and promote efficient design of OER electrocatalysts for renewable energy conversion and storage.

First-principles study of the electronic and catalytic properties of nickel-antimony (Ni-Sb) alloy catalyst for hydrogen evolution reaction

Hydrogen evolution reaction (HER) is a vital half-reaction for water splitting to produce H2. Exploring efficient, affordably priced, and environmentally sustainable HER catalysts is necessary for the development of renewable energy conversion and storage technologies. Here, the HER catalytic activity of hexagonal NiSb(010), hexagonal NiSb(001), hexagonal NiSb(101), cubic Ni3Sb(100), cubic Ni3Sb(010), cubic Ni3Sb(101), orthorhombic Ni3Sb(010), and orthorhombic Ni3Sb(101), is systematically investigated by density functional theory methods. Based on the calculated surface energy, all the studied surfaces are stable. Subsequently, we further evaluate their HER activity by calculating Gibbs free energy of hydrogen adsorption (ΔG*H) and exchange current density (i0). The results show that hexagonal NiSb and orthorhombic Ni3Sb are expected to be promising HER catalysts in Ni-Sb alloys because their ΔG*H values are respectively −0.03 and 0.03 eV, and they have larger i0 values. The synergistic interaction between the metal atoms of Ni and Sb can effectively promote electron transfer between the catalyst and reaction species, which is clearly demonstrated by the electronic structure analysis, which also illustrates that such high catalytic activity can be attributed to it. This work is conducive to guiding the design of this kind of alloy electrocatalysts for HER.

Micro-kinetic modelling of the CO reduction reaction on single atom catalysts accelerated by machine learning.

Electrochemical CO2 transformation to fuels and chemicals is an effective strategy for conversion of renewable electric energy into storable chemical energy in combination with reducing green-house gas emission. Metal-nitrogen-carbon (M-N-C) single atom catalysts (SAC) have shown great potential in the electrochemical CO2 reduction reaction (CO2RR). However, exploring advanced SACs with simultaneously high catalytic activity and high product selectivity remains a great challenge. In this study, density functional theory (DFT) calculations are combined with machine learning (ML) for rapid and high-throughput screening of high performance CO reduction catalysts. Firstly, the electrochemical properties of 99 M-N-C SACs were calculated by DFT and used as a database. By using different machine learning models with simple features, the investigated SACs were expanded from 99 to 297. Through several effective indicators of catalyst stability, inhibition of the hydrogen evolution reaction, and CO adsorption strength, 33 SACs were finally selected. The catalytic activity and selectivity of the remaining 33 SACs were explored by micro-kinetic simulation based on Marcus theory. Among all the studied SACs, Mn-NC2, Pt-NC2, and Au-NC2 deliver the best catalytic performance and can be used as potential catalysts for CO2/CO conversion to hydrocarbons with high energy density. This effective screening method using a machine learning algorithm can promote the exploration of CO2RR catalysts and significantly reduce the simulation cost.

Theoretical investigation on enhanced HER electrocatalytic activities of SiC monolayers through nonmetal doping and strain engineering

Efficient hydrogen evolution reaction (HER) electrocatalysts are crucial for renewable energy storage and conversion.

Rapid microwave synthesis of medium and high entropy oxides for outstanding oxygen evolution reaction performance

Development of efficient and durable catalysts for oxygen evolution reaction (OER) is disparately needed for renewable and sustainable energy storage and conversion. High entropy oxides (HEOs) have gained significant attention...

Unleashing synergistic co-sensitization of BOA dyes and Ru(ii) complexes for dye-sensitized solar cells: achieving remarkable efficiency exceeding 10% through comprehensive characterization, advanced modeling, and performance analysis.

Dye-sensitized solar cells (DSSCs) have emerged as a promising alternative for renewable energy conversion. The synthesis and characterization of the 2-acetonitrile-benzoxazole (BOA) sensitizer MSW-1-4 are presented along with their chemical structures. Four new organic dyes, MSW-1 through MSW-4, were synthesized using BOA as the main building block, with different additional donor groups. The dyes were characterized and their photophysical and electrochemical properties were studied. Computational modeling using density functional theory (DFT) was performed to investigate their potential as sensitizers/co-sensitizers for photovoltaic applications. The modeling showed a distinct charge separation between the donor and acceptor parts of the molecules. For dye-sensitized solar cells, MSW-4 performed the best out of MSW-1-3 and was also better than the reference dye D-5. Moreover, MSW-3 was co-sensitized along with a typical highly efficient bipyridyl Ru(ii) sensitizer, N719, reference dye D-5, and metal-free dye MSW-4, to induce light harvesting over the expanded spectral region and hence improve the efficiency. Co-sensitizer (MSW-3 + N719) showed an improved efficiency of 10.20%. This outperformed a solar cell that used only N719 as the sensitizer, which had an efficiency of 7.50%. The appropriate combined dye loading of MSW-3 + N719 enabled good light harvesting and maximized the photoexcitation. The synergistic effect of using both MSW-3 and N719 as co-sensitizers led to enhanced solar cell performance compared with using N719 alone.

МОДЕЛИРОВАНИЕ КОНЦЕНТРИРОВАННОГО СОЛНЕЧНОГО ИЗЛУЧЕНИЯ ИНФРАКРАСНЫМ ДЛЯ ИЗМЕРЕНИЯ ТЕПЛОВЫХ ХАРАКТЕРИСТИК ТЕПЛОФОТОЭЛЕКТРИЧЕСКОГО МОДУЛЯ СОЛНЕЧНОЙ КОНЦЕНТРАТОРНОЙ УСТАНОВКИ

When developing renewable energy conversion devices, more and more attention is being paid to improving the efficiency of using renewable energy. The efficiency of modern mass-produced solar photovoltaic modules is about 20 percent. In order to increase the completeness of the use of solar energy, the direction of thermal photovoltaic systems is receiving significant development. Devices of this type realize the task of recycling the remaining 80 percent of energy into heat for its subsequent use. The conversion of concentrated solar energy into photoelectricity and heat is carried out by a thermal photovoltaic module. The study of its photovoltaic and thermal parameters is one of the main tasks when creating an appropriate installation. (Research Purpose) The research purpose is developing a methodology and creating a laboratory installation for studying the thermal characteristics of a thermal photovoltaic module. (Materials and methods) The design of the thermal photovoltaic module is presented. The spectral characteristics of the photodetector surface of the module in the visible and infrared spectral ranges have been studied by dispersion and Fourier spectroscopy. (Results and discussion) The analysis of the results of the study of the reflection spectra in the visible and infrared spectral ranges along with the spectral density of the infrared Planck radiation for the temperatures of the infrared emitter in the region of 250-300 degrees Celsius is carried out. The conversion coefficients of the intensities of concentrated solar radiation into the density of the Stefan-Boltzmann infrared radiation flux are obtained. A test measurement of the stationary temperature of the coolant at the output of the module was carried out, according to which the flux density of the heating infrared radiation was calculated. This value is correctly consistent with the independently measured intensity of infrared radiation. (Conclusions) A laboratory measuring stand has been created to simulate concentrated solar radiation with infrared radiation of the thermal range to measure the thermal characteristics of the thermal photovoltaic module of a solar concentrator installation.

Selective oxygen reduction reaction: mechanism understanding, catalyst design and practical application.

The oxygen reduction reaction (ORR) is a key component for many clean energy technologies and other industrial processes. However, the low selectivity and the sluggish reaction kinetics of ORR catalysts have hampered the energy conversion efficiency and real application of these new technologies mentioned before. Recently, tremendous efforts have been made in mechanism understanding, electrocatalyst development and system design. Here, a comprehensive and critical review is provided to present the recent advances in the field of the electrocatalytic ORR. The two-electron and four-electron transfer catalytic mechanisms and key evaluation parameters of the ORR are discussed first. Then, the up-to-date synthetic strategies and in situ characterization techniques for ORR electrocatalysts are systematically summarized. Lastly, a brief overview of various renewable energy conversion devices and systems involving the ORR, including fuel cells, metal-air batteries, production of hydrogen peroxide and other chemical synthesis processes, along with some challenges and opportunities, is presented.

Bimetallic sulfide/N-doped carbon composite derived from Prussian blue analogues/cellulose nanofibers film toward enhanced oxygen evolution reaction.

Exploiting effective, stable, and cost-efficient electrocatalysts for the water oxidation reaction is highly desirable for renewable energy conversion techniques. Constructional design and compositional manipulation are widely used approaches to efficaciously boost the electrocatalytic performance. Herein, we designed a NiFe-bimetallic sulfide/N-doped carbon composite via a two-step thermal treatment of Prussian blue analogues/cellulose nanofibers (PBA/CNFs) film. The NiFe-bimetallic sulfide/N-doped carbon composite displayed enhanced OER performance in an alkaline environment, with an overpotential of 282 mV at 10 mA cm-2, a Tafel slope of 59.71 mV dec-1, and good stability, making the composite a candidate electrocatalyst for OER-related energy equipment. The introduction of CNFs in the precursor prevented the aggregation of PBA nanoparticles (NPs), exposed more active sites, and the resulting carbon substrate enhanced the electroconductivity of the composite. Moreover, the synergistic effect of Ni and Fe in the bimetallic sulfide could modulate the configuration of electrons, enrich the catalytically active sites, and augment the electric conductivity, thus ameliorating the OER performance. This study broadens the application of MOF-CNF composites to construct hierarchical structures of metal compounds and provides some thoughts for the development of cost-effective precious-metal-free catalysts for electrocatalysis.

Pressed Ni/MFe2O4 (M = Ni, Co) powder compacts for application as bifunctional, high-performance electrodes in electrochemical water splitting

The development of active, stable, earth-abundant, and cheap catalysts is crucial for renewable energy conversion devices. Catalysts for electrochemical water splitting are prepared using cold uniaxial pressing and consist of a superficial ferrite coating on a nickel substrate. The activity and mechanism of the oxygen (OER) and hydrogen (HER) evolution reactions on powder compacts are investigated. It is found that powder compacts are efficient catalysts for oxygen and hydrogen evolution in a 1 M KOH solution. For Ni/NiFe2O4, the current density of 10 mAcm−2 in OER and −10 mAcm−2 in HER shows overpotentials of 272 mV and −43 mV, respectively. In turn, for Ni/CoFe2O4, those overpotentials are 279 mV and −37 mV. Furthermore, using the same material for the anode and cathode in a two-electrode cell configuration, one can achieve a 10 mAcm−2 water splitting current at only 1.55 V for over 48 h without coating degradation. It is stated that the high activity towards OER and HER results from the large electrochemically active surface area and high electrical conductivity of powder compacts. The results also indicate that the most probable rate-determining steps for OER and HER are the formation of the adsorbed oxide atom and H2 molecule, respectively.

Seamless Switching Method Between Grid-Following and Grid-Forming Control for Renewable Energy Conversion Systems

Seamless Switching Method Between Grid-Following and Grid-Forming Control for Renewable Energy Conversion Systems

Green synthesis of cobalt ferrite from rotten passion fruit juice and application as an electrocatalyst for the hydrogen evolution reaction

Rotten passion fruits, which are highly available in many countries during some periods of the year, can be used to efficiently produce CoFe2O4 material with special structural and electrochemical characteristics for the hydrogen evolution reaction.