Investigation of a radiative sky cooling module using phase change material as the energy storage

Radiative sky cooling (RSC) systems have enjoyed a privileged position in the research community due to generating cooling energy without consuming electricity using the open atmospheric window and infrared emission to the sky. However, the system's justification occurs when it reaches a temperature below the minimum 24-hour ambient temperature. This study utilizes phase change materials (PCM) as the energy storage of a hybrid daytime photovoltaic-thermal and nighttime RSC module and investigates the nocturnal cooling energy-saving potential of the system at different phase transition temperatures. After being validated by the experimental data in the literature, the simulated model was used for examining the exergy and energy efficiencies of PCMs with varying phase transition temperatures. The comparison of the exergy efficiency in the radiative sky cooling systems was performed for the first time, revealing the simultaneous effect of the temperature drop and cooling power to specify the optimal operative point of the system. Based on the climatic conditions of the simulation site, the PCM with phase transition temperatures of 18 °C revealed the peak and average exergy efficiencies of 42.8% and 33.7%, respectively. Likewise, the 23 °C PCM recorded the maximum cooling power of about 49.9 W/m2, and the 15 °C PCM achieved the highest temperature drop of about 14.8 °C

Hierarchical Co₃O₄/Co(OH)₂ Nanoflakes as a Supercapacitor Electrode: Experimental and Semi-Empirical Model

In this research, facile and low cost synthesis methods, electrodeposition at constant current density and anodization at various applied voltages, were used to produce hierarchical cobalt oxide/hydroxide nanoflakes on top of porous anodized cobalt layer. The maximum electrochemical capacitance of 601 mF cm^–2 at scan rate of 2 mV s^–1 was achieved for 30 V optimized anodization applied voltage with high stability. Morphology and surface chemical composition were determined by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. The size, thickness, and density of nanoflakes, as well as length of the porous anodized Co layer were measured about 460 ± 45 nm, 52 ± 5 nm, 22 ± 3 μm^–2, and 3.4 ± 0.3 μm for the optimized anodization voltage, respectively. Moreover, the effect of anodization voltage on the resulting supercapacitance was modeled by using the Butler–Volmer formalism. The behavior of the modeled capacitance in different anodization voltages was in good agreement with the measured experimental data, and it was found that the role and contribution of the porous morphology was more decisive than structure of nanoflakes in the supercapacitance application

Oxidized graphitic carbon nitride nanosheets as an effective adsorbent for organic dyes and tetracycline for water remediation

Graphitic carbon nitride (g-C3N4) is promising as adsorbent for water remediation as its chemical structure allows a variety of mechanisms to interact with wastewater pollutants. However, several issues, such as low specific surface area and insufficient dispersibility in water, have to be tackled to achieve a competitive performance in such use. Previous attempts to improve the features of g-C3N4as an adsorbent have relied on carbon doping and exfoliation in the solid phase by thermal expansion. Here, we demonstrate that exfoliation in the liquid phase by a combination of oxidation and sonication allows preparing g–C3N4–based materials with improved dispersibility in water, increased exposed surface, and abundance of surface functional groups. The obtained oxidized g-C3N4 adsorbents exhibited high adsorption capacities which were remarkable towards organic dyes (∼70–600 mg/g) and excellent in the case of the antibiotic tetracycline (895 mg/g) in aqueous solution. The present results should open new opportunities for the use of oxidized g-C3N4 materials as adsorbents for water remediation.S. V.-R. and J. I. P gratefully acknowledge financial support from the Spanish Ministerio de Economía y Competitividad (MINECO) and the European Regional Development Fund (ERDF) through project MAT2015-69844-R, as well as the Spanish Ministerio de Ciencia, Innovación y Universidades and the ERDF through project RTI2018-100832-B-I00. Partial funding by Plan de Ciencia, Tecnología e Innovación (PCTI) 2013–2017 del Principado de Asturias and the ERDF (project IDI/2018/000233) is also acknowledged. A. Z. M. thanks Sharif University of Technology and the Iran National Science Foundation (Grant No. 940009) for partial support. M. Y. acknowledges the Iran Elite Foundation for supporting sabbatical leave.Peer reviewe

Group 6 transition metal dichalcogenide nanomaterials : synthesis, applications and future perspectives

Group 6 transition metal dichalcogenides (G6-TMDs), most notably MoS2, MoSe2, MoTe2, WS2 and WSe2, constitute an important class of materials with a layered crystal structure. Various types of G6-TMD nanomaterials, such as nanosheets, nanotubes and quantum dot nano-objects and flower-like nanostructures, have been synthesized. High thermodynamic stability under ambient conditions, even in atomically thin form, made nanosheets of these inorganic semiconductors a valuable asset in the existing library of two-dimensional (2D) materials, along with the well-known semimetallic graphene and insulating hexagonal boron nitride. G6-TMDs generally possess an appropriate bandgap (1–2 eV) which is tunable by size and dimensionality and changes from indirect to direct in monolayer nanosheets, intriguing for (opto)electronic, sensing, and solar energy harvesting applications. Moreover, rich intercalation chemistry and abundance of catalytically active edge sites make them promising for fabrication of novel energy storage devices and advanced catalysts. In this review, we provide an overview on all aspects of the basic science, physicochemical properties and characterization techniques as well as all existing production methods and applications of G6-TMD nanomaterials in a comprehensive yet concise treatment. Particular emphasis is placed on establishing a linkage between the features of production methods and the specific needs of rapidly growing applications of G6-TMDs to develop a production-application selection guide. Based on this selection guide, a framework is suggested for future research on how to bridge existing knowledge gaps and improve current production methods towards technological application of G6-TMD nanomaterials.MOE (Min. of Education, S’pore

Nanorod Array-Based Hierarchical NiO Microspheres as a Bifunctional Electrocatalyst for a Selective and Corrosion-Resistance Seawater Photo/Electrolysis System

Utilizing earth-abundant seawater over scarce freshwater for hydrogen fuel production via water electrolysis is a promising/sustainable strategy. However, the serious anodic corrosion due to the competing chloride oxidation reaction significantly hampers the overall stability of the electrolyzer. Therefore, it demands an efficient and robust catalyst with high selectivity and corrosion resistance for direct seawater splitting. Here, we present a bifunctional catalyst developed by morphology engineering to form nanorod array-based hierarchical NiO microspheres (NRAHM-NiO) as a three-dimensional (3D) hierarchical oxide/hydroxide urchin-like structure material for highly selective seawater splitting against chloride oxidation. Benefitting from highly intrinsic electroactive sites, good charge transferability, fast-releasing gas bubbles, and corrosion resistance as well as hydrophilic surface, the NRAHM-NiO exhibits outstanding bifunctional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic activity toward selective and durable overall seawater splitting. The system requires small cell voltages of 1.66 and 2.01 V to drive current densities of 100 and 500 mA cm-2 at room temperature, respectively. Such catalytic activity is superior compared to the benchmark Pt/C(−)||Pt/C(+) and Pt/C(−)||IrO2(+) pair systems. Importantly, this device demonstrates specific stability as well as selectivity toward the OER in seawater with 99% faradaic efficiency without forming any chlorine species. The experimental results are well supported by density functional theory (DFT) calculations. Powered by a single solar cell, the integrated photolysis system shows 9.9% solar-to-hydrogen (STH) efficiency. © 2023 American Chemical Society.11Nsciescopu

Selecting Support Layer for Electrodeposited Efficient Cobalt Oxide/Hydroxide Nanoflakes to Split Water

Energy and environment crises motivated scientists to develop sustainable, renewable, and clean energy resources mainly based on solar hydrogen. For this purpose, one main challenge is the low cost flexible substrates for designing earth abundant efficient cocatalysts to reduce required water oxidation overpotential. Here, a systematic morphological and electrochemical study has been reported for cobalt oxide/hydroxide nanoflakes simply electrodeposited on four different commercially available substrates, titanium, copper sheet, steel mesh, and nickel foam. Remarkable dependence between the used substrate, morphology, and electrocatalytic properties of nanoflakes introduced flexible porous steel layer as the best substrate for samples with 499 mV overpotential, 5.3 Ω charge transfer resistance, and 0.03 S^–1 turnover frequency. Besides, carbonaceous paste including carbon nanotubes and graphene sheets as the middle layer increased turnover frequency by 33%, effective surface interface nearly three times while it reduced 7.5% of resistance. Hence, optimizing the conductive nanostructured paste can lead to more efficient cobalt electrocatalysts exposing more active atomic surface sites

P‑Doped g‑C₃N₄ Nanosheet-Modified BiVO₄ Hybrid Nanostructure as an Efficient Visible Light-Driven Water Splitting Photoanode

Here, a solution combustion method was employed to construct a photoanode based on bismuth vanadate (BV) composition. To curtail the fast charge recombination, phosphorus-doped g-C3N4 nanosheets (PCNS) in combination with BV are considered a potential approach. The prepared solution combustion facilitated the formation of a BiVO4-PCNS (BV-PCNS) hybrid photoanode with worm-like morphology with a simple setup. The weight ratio of PCNS/BiVO4 and the loading volume/cm2 were optimized to determine the most efficient photoanode. The highest photocurrent density of 0.5 mA/cm2 at 1.23 V vs reversible hydrogen electrode (RHE) under 1 sun illumination was achieved for the hybrid nanostructure at 2 wt % of PCNS/BiVO4 and 50 μL loading volume/cm2 (BV-PCNS2-50), which is fivefold higher than that of the BV control sample. It was found that the presence of PCNS resulted in the formation of mid-gap states to enhance the visible light activity of BV-PCNS. A possible charge transfer mechanism is proposed under photoirradiation to show how the optimized deposition parameters influence the reduction of the electron–hole recombination rate of the photoanode and thus improve its photoelectrochemical water splitting performance. Density functional theory calculations were also performed to find the band alignment type formed across the BV/PCNS interface and to suggest the charge transfer mechanism in the BV/PCNS interface

Two-dimensional materials in semiconductor photoelectrocatalytic systems for water splitting

Hydrogen (H-2) production via solar water splitting is one of the most ideal strategies for providing sustainable fuel because this requires only water and sunlight. In achieving high-yield production of hydrogen as a recyclable energy carrier, the nanoscale design of semiconductor (SC) materials plays a pivotal role in both photoelectrochemical (PEC) and photocatalytic (PC) water splitting reactions. In this context, the advent of two-dimensional (2D) materials with remarkable electronic and optical characteristics has attracted great attention for their application to PEC/PC systems. The elaborate design of combined 2D layered materials interfaced with other SCs can markedly enhance the PEC/PC efficiencies via bandgap alteration and heterojunction formation. Three classes of 2D materials including graphene, transition metal dichalcogenides (TMDs), and graphitic carbon nitride (g-C3N4), and their main roles in the photoelectrocatalytic production of H-2, are discussed in detail herein. We highlight the various roles of these 2D materials, such as enhanced light harvesting, suitable band edge alignment, facilitated charge separation, and stability during the water splitting reaction, in various SC/2D photoelectrode and photocatalytic systems. The roles of emerging 2D nanomaterials, such as 2D metal oxyhalides, 2D metal oxides, and layered double hydroxides, in PEC H-2 production are also discussed.11Nsciescopu