Regulation of hydrogen evolution performance of titanium oxide-carbon composites at high current density with a Ti-O hybrid orbital

Rational design and controllable synthesis of practical electrodes with high sta bility and activity at high current density for a hydrogen evolution reaction(HER)are critical for renewable and sustainable energy conversion.However,high-performance TiO_(2)-based electrocatalysts for HER are quite limited,and the cat alytic active centers still remain elusive.Herein,a simple strategy is demonstrated for the synthesis of TiO_(2)-carbon composite(TiO_(2)/C)with high HER performance and stability.The remarkable HER performance of TiO_(2)/C can be ascribed to the doping of carbon atoms,which leads to stronger hybridization of Ti 3d and O 2p orbitals,thus substantially improving the electrocatalytic efficiency.This study elucidates that the hydrogen evolution activity of oxide electrocatalysts can be largely improved by regulating their electronic structures by doping carbon atoms and also provides an effective strategy for designing heterostructured electro catalysts with high catalytic activity and stability at high current density for HER.

Investigation of kinetic and thermodynamic parameters of coal pyrolysis with model-free fitting methods

Kinetic analyses are important means for understanding the complicated coal pyrolysis process.This work conducted non-isothermal pyrolysis of four low-medium rank coals with thermogravimetric analyzer at different heating rates(5,10 and 20 K/min).Four model-free fitting approaches including KAS,OFW,Starink and Friedman methods were used to analyze pyrolysis kinetics of the coals.Thermodynamic parameters including enthalpy(ΔH)Gibbs free energy(ΔG)and entropy(ΔS)were calculated with the activation values(E)obtained with KAS method.For the kinetic analysis,the KAS,OFW and Starink methods give close E values over the whole conversion range,but the Friedman method shows more deviant results.The thermodynamic favorability of coal pyrolysis is discussed,bothΔH andΔG increase with conversion consistently with the variation of E,revealing that pyrolysis is endothermic and thermodynamic favorability is reduced with conversion rises.The minusΔS implies that coal structures evolve from disordered to organized ones as universally accepted.These results are expected to deepen our understanding and to optimize the conditions of coal pyrolysis.

Boosting chemical looping combustion performances of red mud with transition metal oxides

Red mud(RM)is industrial solid waste that severely threatens environmental safety,and its resource utilization is significant both economically and ecologically.The presence of ferric oxides(Fe_(2)O_(3))makes RM potential oxygen carriers(OC)for chemical looping combustion(CLC),which is a promising,novel and low-carbon combustion technology.This work examined the CLC performance of two kinds of RM using gaseous and solid fuels.Both Fe_(2)O_(3) and alkali and alkaline-earth metals(AAEM)species within RM enhance carbon conversion during CLC.Nevertheless,the reactivity of original RM is unsatisfactory due to its low oxygen transporting capacity(R_(0),lower than 0.1),carbon conversion(X_(C),less than 0.8),CO_(2) selectivity(Y_(CO_(2)),less than 0.9)and instable performance.Transition metal oxides including CuO and NiO were used to modify the RM through wet impregnation.Both oxides notably improve RM performances,i.e.,X_(C) and Y_(CO_(2)) are notably increased.Still,deteriorations during redox cycles are observed because of particle agglomeration and sintering,especially for the RM modified with NiO.Considering the cost,potential environmental risk and efficacy,CuO is superior to NiO thanks to the enhanced performances of the modified RM-based OC including higher X_(C)(about 0.9),Y_(CO_(2))(approximately 1)and stronger sintering resistance.

Fractionation and characterization of thermal extracts from lignite under ultrasonic-assisted extraction

Hypercoal(HPC)is promising feedstock for producing coal-based chemicals due to its extremely low ash content and high reactivity.However,the conventional methods for HPC preparation through thermal extraction under mechanical stirring are difficult to scale-up due to the low HPC yield and large consumption of solvent.This work conducted ultrasonic-assisted extraction(UAE)instead of mechanical stirring to enhance the efficiency of HPC production,and the effect of technological conditions on the HPC yield were examined.It was found that the UAE could remarkably enhance the HPC yield from 52.3%to 82.4%.Moreover,the ratio of soluble(HPC-S)to deposit(HPC-D)increased from 1.65 to 2.85,verifying the high efficiency and the capacity of altering the product distribution of UAE.