Highly flame-retardant polyurethane foam based on reactive phosphorus polyol and limonene-based polyol

Polyurethane foams are in general flammable and their flammability can be controlled by adding flame-retardant (FR) materials. Reactive FR have the advantage of making strong bond within the polyurethane chains to provide excellent FR over time without compromising physico-mechanical properties. Here, phenyl phosphonic acid and propylene oxide-based reactive FR polyol was synthesized and used along with limonene based polyol for preparation of FR polyurethanes. All the obtained foams showed higher closed cell content (above 96%). By the addition of FR–polyol, the compressive strength of the foams showed 160% increment which could be due to reactive nature of FR–polyol. Moreover, 1.5 wt % of phosphorus (P) content reduced the self-extinguishing time of the foam from 81 (28% weight loss) to 11.2 s (weight loss of 9.8%). Cone test showed 68.6% reduction in peak heat release rate along with 23.4% reduction in thermal heat release. The change in char structure of carbon after burning was analyzed using Raman spectra which, suggests increment in the graphitic phase of the carbon over increased concentration of phosphorus. It can be concluded from this study that phosphorous based polyol could be blended with bio-based polyols to prepare highly FR and superior physico-mechanical rigid polyurethane foams. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46224

Highly flame-retardant bio-based polyurethanes using novel reactive polyols

Poor flame retardancy of polyurethanes (PU) is a global issue as it limits their applications particularly in construction, automobile, and household appliances industries. The global challenge of high flammability of PU can be addressed by incorporating flame-retardant materials. However, additive flame-retardants are non-compatible and depreciate the properties of PU. Hence, reactive flame-retardants (RFR) based on aliphatic (Ali-1 and Ali-2) and aromatic (Ar-1 and Ar-2) structured bromine compounds were synthesized and used to prepare bio-based PU using limonene dimercaptan. The aromatic bromine containing foams showed higher close cell content (average 97 and 100%) and compressive strength (230 and 325 kPa) to that of aliphatic bromine containing foams. Similar behavior was observed for a horizontal burning test where with a low concentration of bromine (5 wt %) in the foams for Ar-1 and Ar-2 displayed a burning time of 12.5 and 11.8 s while, Ali-1 and Ali-2 displayed burning time of 25.7 and 37 s, respectively. Neat foam showed a burning time of 74 s. The percentage weight loss for neat PU foam was 26.5%, while foams containing 5 wt % bromine in Ali-1, Ali-2, Ar-1, and Ar-2 foams displayed weight loss of 11.3, 14, 7.9, and 14%, respectively. Our results suggest that flame retardant PU foams could be prepared effectively by using RFR materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46027

Flower-shaped cobalt oxide nano-structures as an efficient, flexible and stable electrocatalyst for the oxygen evolution reaction

The industrial application of water splitting for oxygen evolution requires low cost, high performance and stable electrocatalysts which can operate at low overpotential. Here, we develop a high performance and stable electrocatalyst for the oxygen evolution reaction (OER) using earth abundant materials. A binder free approach for the synthesis of flower-shaped cobalt oxide (Co3O4) composed of nanosheets showed high OER catalytic activity. The Co3O4 electrode requires a low overpotential of 356 mV to achieve a current density of 10 mA cm-2 with a low onset potential of 284 mV. The electrode showed outstanding flexibility and stability. The catalytic activity of the Co3O4 electrode was very stable up to the 2000th cycle of the polarization study. The high catalytic activity and structural stability arise due to efficient and fast charge transportation through the nanosheets of Co3O4 which are in direct contact with the conducting nickel of the electrode. The porous structure of Co3O4 allows easy access of the electrolyte and escape of generated oxygen without damaging the structure. Collectively, the flower-shaped nanostructured Co3O4 electrode can be used as a flexible and high performance electrode for the OER in an industrial setup

Nitrogen-doped flexible carbon cloth for durable metal free electrocatalyst for overall water splitting

Water electrolysis is one of the greenest ways to generate clean energy. However, it is critical to develop durable and cost-effective electrocatalysts using earth-abundant materials for overall water splitting. Here we report, a facile method to fabricate N-doped cotton cloth as an electrocatalyst. The N-doped cotton cloth showed outstanding performance as an electrocatalyst for overall water splitting. For oxygen evolution reaction (OER), N-doped cotton cloth requires a low overpotential of 351 mV to deliver 10 mA/cm2 of current density with a Tafel slope of 88 mV/dec. On the other hand, it requires 233 mV to achieve a current density of 10 mA/cm2 for hydrogen evolution reaction (HER) with a Tafel slope of 135 mV/dec. Furthermore, the electrocatalyst showed outstanding electrocatalytic stability and flexibility. The observed overpotential and stability are among the best for the metal-free electrocatalyst. Such a binder-free approach for fabrication of high performance, durable and flexible bi-functional (HER and OER) electrocatalyst could be a promising way to generate green energy from water

MoS2 Decorated Carbon Nanofibers as Efficient and Durable Electrocatalyst for Hydrogen Evolution Reaction

Hydrogen is an efficient fuel which can be generated via water splitting, however hydrogen evolution occurs at high overpotential, and efficient hydrogen evolution catalysts are desired to replace state-of-the-art catalysts such as platinum. Here, we report an advanced electrocatalyst that has low overpotential, efficient charge transfers kinetics, low Tafel slope and durable. Carbon nanofibers (CNFs), obtained by carbonizing electrospun fibers, were decorated with MoS2 using a facile hydrothermal method. The imaging of catalyst reveals a flower like morphology that allows for exposure of edge sulfur sites to maximize the HER process. HER activity of MoS2 decorated over CNFs was compared with MoS2 without CNFs and with commercial MoS2. MoS2 grown over CNFs and MoS2-synthesized produced about 374 and 98 times higher current density at −0.30 V (vs. Reversible Hydrogen Electrode, RHE) compared with the MoS2-commercial sample, respectively. MoS2-commercial, MoS2-synthesized and MoS2 grown over CNFs showed a Tafel slope of 165, 79 and 60 mV/decade, capacitance of 0.99, 5.87 and 15.66 mF/cm2, and turnover frequency of 0.013, 0.025 and 0.54 s−1, respectively. The enhanced performance of MoS2-CNFs is due to large electroactive surface area, more exposure of edge sulfur to the electrolyte, and easy charge transfer from MoS2 to the electrode through conducting CNFs