Kinetics of reductive leaching of manganese oxide ore using cellulose as reductant

The kinetics of reductive leaching of manganese from a low-grade manganese oxide ore were studied using cellulose as reductant in dilute sulfuric acid medium.It was found that when the stirring speed was higher than 200 r/min,the effect of gas film diffusion on manganese extraction efficiency could be neglected,and the kinetic behavior was investigated under the condition of elimination of external diffusion influence on the leaching process.Effects of leaching temperature,mass ratio of cellulose and ore,and the sulfuric acid concentration on manganese extraction efficiency were discussed.The kinetic data were analyzed based on the shrinking core model,which indicated that the leaching process was dominated by both ash layer diffusion and chemical reaction at the initial stage,with the progress of leaching reaction,the rate-controlling step switched to the ash layer diffusion.It was also concluded that the sulfuric acid concentration had the most significant influence on the leaching rate,the reaction orders with respect to the sulfuric acid concentration were 2.102 in the first 60 min,and 3.642 in the later 90 min,while the reaction orders for mass ratio of cellulose and ore were 0.660 and 0.724,respectively.An Arrhenius relationship was used to relate the temperature to the rate of leaching,from which apparent activation energies were calculated to be 46.487 kJ/mol and 62.290 kJ/mol at the two stages,respectively.Finally,the overall leaching rate equations for the manganese dissolution reaction with cellulose in sulphuric acid solution were developed.The morphological changes and mineralogical forms of the ore before and after the chemical treatment were discussed with the support of SEM and XRD analyses.

Regulating the electronic structure of NiFe layered double hydroxide/reduced graphene oxide by Mn incorporation for high-efficiency oxygen evolution reaction

The development of highly efficient and costeffective oxygen evolution reaction(OER)electrocatalysts for renewable energy systems is vitally essential.Modulation of the electronic structure through heteroatom doping is considered as one of the most potential strategies to boost OER performances.Herein,a rational design of Mn-doped NiFe layered double hydroxide/reduced graphene oxide(Mn-NiFe LDH/rGO)is demonstrated by a facile hydrothermal approach,which exhibits outstanding OER activity and durability.Experimental results and density functional theory(DFT)calculations manifest that the introduction of Mn can reprogram the electronic structure of surface active sites and alter the intermediate adsorption energy,consequently reducing the potential limiting activation energy for OER.Specifically,the optimal Mn-NiFe LDH/rGO composite shows an enhanced OER performance with an ultralow overpotential of 240 mV@10 mA cm^(-2),Tafel slope of 40.0 mV dec^(-1) and excellent stability.Such superior OER activity is comparable to those of the recently reported state-of-the-art OER catalysts.This work presents an advanced strategy for designing electrocatalysts with high activity and low cost for energy conversion applications.

Efficient solar fuel production with a high-pressure CO_(2)-captured liquid feed

We demonstrated an efficient solar photovoltaic-powered electrochemical CO_(2) reduction device with a high-pressure CO_(2)-captured liquid feed.In an“air-to-barrel”picture,this device holds promise to avoid both high-temperature gaseous CO_(2) regeneration and high energy-cost gas product separation steps,while these steps are necessary for devices with a gaseous CO_(2) feed.To date,solar fuel production with a CO_(2)-saturated liquid feed suffers from high over-potential to suppress the hydrogen evolution reaction and consequently,low solar-to-chemical(STC)energy conversion efficiency.Here,we presented a distinct high-pressure operando strategy,i.e.,we took extra advantage of the high pressure in catalyst synthesis besides in the period of the CO_(2) reduction reaction(CO_(2)RR).The power of this strategy was demonstrated by a proof-of-concept device in which a representative copper catalyst was first synthesized in operando in a high-pressure(50 bar)CO_(2)-saturated KHCO3 solution,and then this high-pressure CO_(2)-captured liquid was converted to solar fuel using the operando synthesized Cu catalyst.This Cu catalyst achieved 95%CO_(2)RR selectivity at the recorded low potential of−0.3 V vs.RHE enabled by the combination of operando facet engineering and oxide derivation.Furthermore,this device achieved a record-high STC efficiency of 21.6%under outdoor illumination,superior to other CO_(2)-saturated liquid-fed devices,and compared favorably to gaseous CO_(2)-fed devices.