Unveiling the role of carbon defects in the exceptional narrowing of m-ZrO2 bandgap for enhanced photoelectrochemical water splitting performance

The development of efficient photoelectrodes via defect engineering of wide-band gap metal oxides has been the prime focus for many years. Specifically, the effect of carbon defects in wide-band gap metal oxides on their performance in photoelectrochemical (PEC) applications raised numerous controversies and still elusive. Herein, the effect of various carbon defects in m-ZrO2 was investigated using the density functional theory to probe the thermodynamic, electronic, and optical properties of the defective structures against pristine m-ZrO2. The defect formation energies revealed that elevating the temperature promotes and facilitates the formation of carbon defects. Moreover, the binding energies confirmed the stability of all studied complex carbon defects. Furthermore, the band edge positions against the redox potentials of water species revealed that all the studied defective structures can serve as photoanodes for water splitting. Additionally, CO3c (carbon atom substituted O3c site) was the only defective structure that exhibited slight straddling of the redox potentials of water. Importantly, all investigated defective structures enhanced light absorption with different optical activities. Finally, CO3cVO3c (carbon atom substituted O3c associated with O3c vacancy) defective m-ZrO2 enjoyed low direct band gap (1.9 eV), low defect formation energy, low exciton binding energy, high mobility of charge carriers, fast charge transfer, and low recombination rate. Concurrently, its optical properties were exceptional in terms of high absorption, low reflectivity and improved static dielectric constant. Hence, the study recommends CO3cVO3c defective m-ZrO2 as the leading candidate to serve as a photoanode for PEC applications

Toward the Proper Selection of Carbon Electrode Materials for Energy Storage Applications: Experimental and Theoretical Insights

Identifying the proper carbon material is one of the key requirements in developing high-performance supercapacitor electrodes. Carbon nanotubes (CNTs), graphene nanoplatelets (GNPs), and graphite (Gr) are commonly used carbon allotropes for supercapacitor applications. The performance of those materials depends on the electrolyte used and the operating potential window. However, those parameters have rarely been investigated and explained. Herein, we present a roadmap for the proper selection of carbon materials in supercapacitor applications via the investigation of the behavior of CNTs, GNPs, and Gr in different electrolytes using both electrochemical and computational tools. The charge storage mechanism was found to be electrolyte-dependent. In terms of the operating potential window, the best performance was obtained upon the use of a Na2SO4 electrolyte, which enabled a potential window of -1 to 0.9, while in terms of capacitance, the positive electrodes in a H2SO4 electrolyte exhibited the highest capacitance. H2SO4 enabled keto-enol tautomerism in the positive potential window and can enlarge the potential window to 1 V. Quantum capacitance calculations helped to identify the reasons behind the obtained different performances in the negative and positive potential windows. For example, upon the identification of the proper electrolyte and potential window, it was possible to obtain a capacitance as high as 453.60 F/g at 5 mV/s in a potential window of 1 V for CNTs, which are much higher than those reported in the literature. Moreover, the guidelines were successfully used to develop a symmetric device that delivers a specific energy of 23.3 Wh/kg and a specific power of 475 W/kg with a stability of 97.8% after 5000 cycles over a potential window of 1.9 V, which are much higher than those reported for CNTs-based symmetric devices

Rb intercalation enhanced the supercapacitive performance of layer-structured MoS2as a 2D model material

Intercalation of alkali metals has proved to be an effective approach for the enhancement of the energy storage performance in layered-2D MoS2. However, the research so far has been limited to the Li and Na ion intercalation with K ions being recently investigated. Herein, we demonstrate, for the first time, the extraordinary capacitance performance of Rb-ion intercalation in the inter-layer of the 1T, 2H, and 3R MoS2 polymorphs. This work elucidates the capacitance performance in terms of quantum capacitance and intercalation strength. Rb-Intercalation into MoS2 layers stabilizes the 1T phase more than Li ions and imparts metallic behavior to the semiconducting 2H and 3R phases. Concurrently, the quantum capacitance of the three phases dramatically increases, surpassing that of graphene and doped graphene. The calculated quantum capacitance can reach as high as 2700, 3250, and 3300 F g-1 for the 1T, 2H, and 3R phases, respectively, rendering the Rb ion a superior choice for boosting the energy storage performance of the MoS2-based supercapacitor electrodes

Supercapattery electrode materials by Design: Plasma-induced defect engineering of bimetallic oxyphosphides for energy storage

Although transition metal hydroxides are promising candidates as advanced supercapattery materials, they suffer from poor electrical conductivity. In this regard, previous studies have typically analyzed separately the impacts of defect engineering at the atomic level and the conversion of hydroxides to phosphides on conductivity and the overall electrochemical performance. Meanwhile, this paper uniquely studies the aforementioned methodologies simultaneously inside an all-in-one simple plasma treatment for nickel cobalt carbonate hydroxide, examines the effect of altering the nickel-to-cobalt ratio in the binder-free defect-engineered bimetallic Ni-Co system, and estimates the respective quantum capacitance. Results show that the concurrent defect-engineering and phosphidation of nickel cobalt carbonate hydroxide boost the amount of effective redox and adsorption sites and increase the conductivity and the operating potential window. The electrodes exhibit ultra-high-capacity of 1462 C g, which is among the highest reported for a nickel-cobalt phosphide/phosphate system. Besides, a hybrid supercapacitor device was fabricated that can deliver an energy density of 48 Wh kg at a power density of 800 W kg, along with an outstanding cycling performance, using the best performing electrode as the positive electrode and graphene hydrogel as the negative electrode. These results outperform most Ni-Co-based materials, demonstrating that plasma-assisted defect-engineered Ni-Co-P/PO is a promising material for use to assemble efficient energy storage devices

Towards Cs-ion supercapacitors: Cs intercalation in polymorph MoS2as a model 2D electrode material

Intercalation of alkali metals has proved to be an effective approach for the enhancement of the energy storage performance in layered-2D materials. However, the research so far has been limited to Li and Na ion intercalation with K ions being recently investigated. Although cesium (Cs) salts are highly soluble in water, Cs+intercalation has been addressed neither in batteries nor in supercapacitors so far. Herein, we demonstrate the exceptional effect of Cs+intercalation in MoS2as a model 2D material to boost its performance as a potential supercapacitor electrode. Cs+intercalation was found to stabilize the metastable 1T phase and increase the conductivity of the 2H and 3R phases. Cs+-Intercalated 1T MoS2showed higher quantum capacitance (CQ) than doped graphene