With every moving day, the aspect that is going to be the most important for modern science and technology is the means to supply sufficient energy for all the scientific applications. As the resource of fossil fuel is draining out fast, an alternative is always required to satisfy the needs of the future world. Limited resources also force to innovate something that can utilise the resource more efficiently. This work is based on a simple synthesis route of biomass derived hard carbon and to exploring the possibility of using it as electrochemical supercapacitors. A cheap, eco-friendly and easily synthesized carbon material is utilized as electrode for electrochemical energy-storage. Four different hard carbons were synthesized from KOH activated banana stem (KHC), phosphoric acid treated banana stem derived carbons (PHC), corn-cob derived hard carbon (CHC) and potato starch derived hard carbons (SHC) and tested as supercapacitor electrodes. KOH-activated hard carbon has provided 479.23 F/g specific capacitance as calculated from its cycle voltammograms. A detailed analysis is done to correlate the results obtained with the material property. Overall, this work provides an in depth analysis of the science behind the components of an electrochemical energy-storage system as well as why the different characterization techniques are required to assess the quality and reliability of the material for electrochemical supercapacitor applications.

Catalyzing hydrogen evolution reaction in alkali media is challenging owing to the sluggish kinetics, originated from the water dissociation process. In this context, synergistic coupling between Ni/Co-based materials with transition metal dichalcogenides (TMDs) often accelerates the alkaline hydrogen evolution reaction (HER). Significant interaction between the two components and active-site density are the keys for achieving a promising catalytic activity. This report emphasizes a two-step selenization approach to prepare a Ni0.85Se/MoSe2 interfacial structure with abundant active sites. Initially, Ni0.75Se nanoparticles were prepared using the solvothermal method and subsequently employed them as a support for the growth of MoSe2 under hydrothermal conditions. This resulted in the formation of a Ni0.85Se/MoSe2 interfacial structure. The results of physical characterization techniques confirm the significant interaction between Ni0.85Se and MoSe2. The interfacial structures showed a superior HER activity in alkali media compared to the individual components; especially, Ni0.85Se/MoSe2 (20) delivers a current density of 10 mA cm–2 at an overpotential of 108 mV. The improved HER activity of the interfacial structure is attributed to the (i) efficient water dissociation process over the Ni0.85Se promoter and (ii) exposure of more catalytic active sites (edges) of MoSe2. In addition, as-prepared Ni0.75Se exhibits a better oxygen evolution reaction (OER) activity by delivering a current density of 10 mA cm–2 at an overpotential of 340 mV. Furthermore, overall water splitting has been demonstrated by constructing an electrolyzer using Ni0.85Se/MoSe2 (20) and Ni0.75Se as a cathode and anode, respectively. The electrolyzer delivers a current density of 10 mA cm–2 at a cell potential of 1.7 V. The long-term stability experiment and the post catalytic characterization reveals the high robustness of the Ni0.85Se/MoSe2 interfacial structure.

Understanding the effect of molybdate incorporation on the structure, morphology, porosity, surface area and etching-induced enhanced electrocatalytic water splitting of low-cost transition metal hydroxides grown on inexpensive copper substrate.

Porous cobalt oxide (Co3O4) nanorod (50-100 nm) and nanosheet-like (70-100 nm) particles were synthesized by a facile hydrothermal method at 150 °C for 2-5 h and 12-24 h, respectively, using aqueous-based precursors like cobalt nitrate, urea and water in the absence of any templating agents followed by their calcination at 300 °C. Morphology and textural properties were tuned by changing the synthesis time at 150 °C. A 3D architecture of Co3O4 was formed by the self-assembly of nanostructured (nanorod and nanosheet) particles. The BET surface area, pore volume and pore diameter of the sample prepared at 150 °C for 5 h were 112 m(2) g(-1), 0.5 cm(3) g(-1) and 7.4 nm, respectively, and it exhibited the highest catalytic performance with a rate constant of 56.8 × 10(-3) min(-1) for the degradation of Chicago Sky Blue 6B, a carcinogenic azo dye used in the textile, paper and food industries. Rod-like particles with a mesoporous structure rendered a better catalytic efficiency than sheet-like particles having both microporous and mesoporous structures. An interrelationship amongst the morphology, textural properties and the catalytic efficiency of Co3O4 was established.

Despite predictions of high electrocatalytic OER activity by selenide-rich phases, such as NiCo 2 Se 4 and Co 3 Se 4 , their synthesis through a wet-chemical route remains a challenge because of the high sensitivity of the various oxidation states of selenium to the reaction conditions. In this work, we have determined the contribution of individual reactants behind the maintenance of conducive solvothermal reaction conditions to produce phase-pure NiCo 2 Se 4 and Co 3 Se 4 from elemental selenium. The maintenance of reductive conditions throughout the reaction was found to be crucial for their synthesis, as a decrease in the reductive conditions over time was found to produce nickel/cobalt selenites as the primary product. Further, the reluctance of Ni(II) to oxidize into Ni(III) in comparison to the proneness of Co(II) to Co(III) oxidation was found to have a profound effect on the final product composition, as a deficiency of ions in the III oxidation state under nickel-rich reaction conditions hindered the formation of a monoclinic "Co 3 Se 4 -type" phase. Despite its lower intrinsic OER activity, Co 3 Se 4 was found to show geometric performance on a par with NiCo 2 Se 4 by virtue of its higher textural and microstructural properties.

Developing electrocatalysts with abundant active sites is a substantial challenge to reduce the overpotential requirement for the alkaline oxygen evolution reaction (OER). In this work, we have aimed to improve the catalytic activity of cobalt selenides by growing them over the self-supported Co3O4 microrods. Initially, Co3O4 microrods were synthesized through annealing of an as-prepared cobalt oxalate precursor. The subsequent selenization of Co3O4 resulted in the formation of a grainy rodlike Co3O4/Co0.85Se/Co9Se8 network. The structural and morphological analysis reveals the presence of Co3O4 even after the selenization treatment where the cobalt selenide nanograins are randomly covered over the Co3O4 support. The resultant electrode shows superior electrocatalytic activity toward OER in alkaline medium by delivering a benchmark current density of 10 mA/cm2 geo at an overpotential of 330 mV. As a comparison, we have developed Co0.85Se/Co9Se8 under similar conditions and evaluated its OER activity. This material consumes an overpotential of 360 mV to deliver the benchmark current density, which signifies the role of the Co3O4 support to improve the electrocatalytic activity of Co0.85Se/Co9Se8. Despite having a low TOF value for Co3O4/Co0.85Se/Co9Se8 (0.0076 s–1) compared to Co0.85Se/Co9Se8 (0.0102 s–1), the improved catalytic activity of Co3O4/Co0.85Se/Co9Se8 is attributed to the presence of a higher number of active sites rather than the improved per site activity. This is further supported from the C dl (double layer capacitance) measurements where Co3O4/Co0.85Se/Co9Se8 and Co0.85Se/Co9Se8 tender C dl values of about 8.19 and 1.08 mF/cm2, respectively, after electrochemical precondition. As-prepared Co3O4/Co0.85Se/Co9Se8 also manifests rapid kinetics (low Tafel slope ∼ 91 mV/dec), long-term stability, low charge-transfer resistance, and 82% Faradaic efficiency for alkaline electrocatalysis (pH = 14). Furthermore, the proton reaction order (ρRHE) is found to be 0.65, indicating a proton decoupled electron transfer (PDET) mechanism for alkaline OER. Thus, the Co3O4 support helps in the exposure of more catalytic sites of Co0.85Se/Co9Se8 to deliver the improved catalytic activities in alkaline medium.

In this work, we report an efficient synthesis approach of disodium terephthalate and its application as a potential battery anode material. Disodium terephthalate is upcycled from waste polyethylene terephthalate flakes with the aid of an ultrafast microwave irradiation process within 2 minutes. The phase and chemical purity of the as-synthesized disodium terephthalate is confirmed by X-ray diffraction, Fourier-transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy. The electrochemical behavior of this low-cost, environmentally benign organic molecular compound is studied in Li-and Na-ion cells. The density functional theory-based calculations are performed to get insights into specifics of electronic properties of Li-and Na-ion cells and rationalize the differences in behavior for the two systems. The delithiation potential of a disodium terephthalate anode is found to be approximately 0.65 V higher than the desodiation potential. The disodium terephthalate-carbon black (Super P) composite electrode delivers discharge capacities of 182 and 224 mAh g −1 at a current density of 25 mA g −1 after 50 cycles in Li-ion and Na-ion cells, respectively. The better C-rate performance of the composite anode for a Li-ion cell, as compared to a Na-ion cell, is due to inferior mobility of Na-ions in the electrode material, which is largely defined by ion size.

The electrocatalytic oxygen evolution reaction (OER) demands an efficient catalyst with low overpotential, rapid kinetics, and long-term stability. Herein, we demonstrate the activity of molybdenum oxide (MoO 2 )-embedded cobalt oxalate (CoC 2 O 4 • 2H 2 O) nanostructures for the OER process. The excellent performance of the microrod-like MoO 2 /CoC 2 O 4 •2H 2 O composite is reflected in just 330 mV overpotential for 10 mA/cm geo 2 , low Tafel slope (78 mV/dec), 90% faradaic efficiency, and 24 h stability in 1.0 (M) KOH. The as-prepared electrocatalyst requires a significantly lower overpotential wrt CoC 2 O 4 •2H 2 O. Incorporation of MoO 2 elegantly modified the textural property, such as surface area and porosity, of the as-prepared material. Furthermore, MoO 2 / CoC 2 O 4 •2H 2 O was found to follow the proton-decoupled electrontransfer mechanism for electrocatalyzing OER. Postcatalytic characterization revealed the electrochemical transformation of a one-dimensional (1-D) MoO 2 /CoC 2 O 4 •2H 2 O microrod into a sheetlike two-dimensional α-Co(OH) 2 /CoOOH during alkaline OER. Interestingly, postcatalytic X-ray photoelectron spectroscopy, inductively coupled plasma, and energy-dispersive X-ray spectroscopy analyses suggest MoO 2 etching from the material, leading to exposure of a higher number of electrochemically active sites that otherwise lay inactive because of their presence in the bulk. Both CoC 2 O 4 •2H 2 O-and MoO 2 /CoC 2 O 4 •2H 2 O-integrated 1-D nanostructures showed an ∼0.01 s −1 turnover frequency value at 400 mV overpotential.We believe that the enhancement in geometrical electrocatalytic activity is not due to the direct participation of MoO 2 in catalysis but due to its electrochemical etching, which makes a higher number of catalytically active sites accessible to the electrolyte. This study conveys the in situ electrochemical activation strategy through etching of pore additive for the alkaline OER process.