高活性方形氧化铅与可视化电解槽协同促进电催化臭氧生产

臭氧是一种环境友好型氧化剂,可直接用于消毒、杀菌和废水处理,对于维护和促进公共卫生安全至关重要.由于臭氧容易分解,不利于储存,因此需要现制即用.目前臭氧生成技术主要包括:电晕放电法和电催化臭氧生产(EOP)技术.相较于电晕放电法,EOP是一种本质安全的臭氧生产技术.然而,该工艺相较于电晕放电技术电能消耗量大,为了使其更具商业可行性,有必要开发高活性且低成本的电催化剂.此外,合理的电解槽设计对于实现高效EOP过程也至关重要.然而,目前研究主要集中在提高EOP催化剂活性方面,对电解槽的结构设计优化的关注较少.本文通过开发高效电催化剂进而将其应用于结构优化后的电解槽中,实现了更加高效的EOP过程.本文采用水热方法成功制备了一种具有较高EOP活性的方形氧化铅(PbO_(x)-CTAB-120)电催化剂.在标准三电极测试系统中,电流密度为50 mA cm^(-2)的测试条件下,法拉第效率(FE)可达20.7%,与商用β-PbO_(2)(17.1%)相比提高了21.1%.此外,设计了具有平行流场的可视化EOP电解槽,该可视化电解槽在传质和传热方面具有明显优势,有利于实现更加高效的EOP过程.将催化剂PbO_(x)-CTAB-120组装至可视化电解槽中,在1.0 A cm^(-2)的测试电流密度下,电解液为超纯水,该体系气态臭氧产量可以达到588 mg h^(-1)g^(-1)catalyst,比能量消耗(PEOP)为56 Wh g^(-1)gaseous ozone.体系臭氧产量约为商用β-PbO_(2)在传统电解槽中产量的2倍,并且PEOP降低率超过62%.原位18O同位素标记差分电化学质谱和密度泛函理论计算结果表明,PbO_(x)-CTAB-120电催化剂在EOP过程中遵循晶格氧机理路径,晶格氧迁移产生的氧空位能有效稳定OOH^(*)和O_(2)^(*)反应中间体,因此有利于催化剂在EOP过程中保持较好的反应活性和稳定性.同时,还利用先进的高速摄像可视化工具和计算流体力学(CFD)仿真模拟研究了平行流场EOP电解槽的运行过程和高效传质传热的原理.CFD模拟结果表明,与传统流场模型相比,平行流场对应的出口气泡停留时间更长,说明平行流场更有利于产物气泡从出口逸出,即气泡容易快速扩散,与实验结果一致.因此,PbO_(x)-CTAB-120电催化剂与新型可视化电解槽相结合,有助于在超纯水中实现较好的气态臭氧产率和较低比能耗.此外,二者的结合充分发挥了电催化剂的EOP活性和电解槽的传质特性所带来的优势,实现了反应性和传输性的协同增强,从而极大促进了原位有机污染物降解效率.综上所述,本文在制备高效阳极催化剂的基础上,同时利用优化电解槽结构实现了提升臭氧产率和降低过程能耗,为高活性电催化剂与优化的电解槽耦合以实现高效EOP过程及其有效应用提供参考.

Trace water triggers high-efficiency photocatalytic hydrogen peroxide production

Photocatalytic production of hydrogen peroxide(H_(2)O_(2))has attracted much attentions as a promising method for sustainable solar fuel.Here,we demonstrate that trace water can drastically boost highefficiency photocatalytic production of H_(2)O_(2) with a record-high concentration of 113 mmol L^(-1) using alkali-assisted C_(3)N_(4) as photocatalyst in water/alcohol mixture solvents.By electron paramagnetic resonance(EPR)measurement,the radical species generated during the photocatalytic process of H_(2)O_(2) are identified.We propose alcohol is used to provide and stabilize-OOH radicals through hydrogen bond,while trace water could trigger photocatalytic production of H_(2)O_(2) via providing and transferring indispensable free protons to completely consume OOH radicals,which breaks the reaction balance of-OOH radical generation from alcohol.Thus-OOH radicals could be supplied by alcohol continuously to serve as a reservoir for high-efficiency production of H_(2)O_(2).These results pave the way towards photocatalytic method on semiconductor catalysts as an outstanding approach for production of hydrogen peroxide.

Doped-nitrogen enhanced the performance of Nb_(2)CT_(x)on the electrocatalytic synthesis of H_(2)O_(2)

Electrochemical oxygen reduction reaction(ORR)for preparing hydrogen peroxide(H_(2)O_(2))is a promising way to replace the anthraquinone method.The key to H_(2)O_(2)production is the development of catalysts to regulate the oxygen reduction reaction pathway.Here,nitrogen-doped Nb_(2)CT_(x)was prepared by NH3 annealing method.Compared with precursor Nb_(2)AlC(67.01%)and pure Nb_(2)CT_(x)(75.70%),nitrogen-doped Nb_(2)CT_(x)exhibited excellent performance for 2e−ORR with>90%H_(2)O_(2)selectivity(at 0.4 V vs.reversible hydrogen electrode(RHE)).Faradic efficiency of nitrogen-doped Nb_(2)CT_(x)reached 80.75%,whereas those for Nb2AlC and Nb_(2)CT_(x)were 60.35%and 39.27%,respectively.A desirable catalytic stability for 50 h was observed.Density functional theory(DFT)calculations indicated excellent activity of the nitrogen-doped Nb_(2)CT_(x)was attributed to the introduction of N.This excellent activity was conducive to the adsorption of oxygen and promoted the formation of the OOH intermediate.This work can serve as an important reference for regulating the electronic structure of MXene to expand the application area in the electrochemical field.

Tuning the ratio of Bi/Bi_(2)O_(3)in Bi/PNC nanosheet for highefficiency electrosynthesis hydrogen peroxide

Electrocatalytic two-electron oxygen reduction reaction(2e-ORR)is a promising method for producing green and sustainable H_(2)O_(2)but lacks high selectivity and yields electrocatalysts.And it is critical to develop catalysts that meet industrial demands.Herein,we report the different ratios of Bi0/Bi^(3+)supported on a phosphorus,nitrogen,and carbon nanosheet(Bi/PNC),which can reduce O_(2) to H_(2)O_(2)with high selectivity(up to 97.75%at 0.4 VRHE)in 0.1 M KOH electrolyte and retain 97%selectivity even after 100 h electrolysis.Then a homemade flow-cell system was built for electrocatalytic production of H_(2)O_(2)under an O_(2) atmosphere using an improved gas diffusion electrode.The Bi/PNC-4 can achieve a high H_(2)O_(2)yield of 2.76 mol·gcatalyst^(-1)·h^(-1)(alkaline),5.29 mol·gcatalyst^(-1)·h^(-1)(neutral),and 3.50 mol·gcatalyst^(-1)·h^(-1)(acid)in universal pH conditions.The in-situ generated H_(2)O_(2)can function as a degradation agent for efficiently degrading pesticides and antibiotics.The outstanding selectivity and activities are attributed to the synergistic effects of Bi0 and Bi^(3+)that promote proton-coupled reduction of O_(2) to OOH^(*)(ΔGOOH^(*)=4.27 eV),and the formation of H_(2)O_(2).The fast yield of H_(2)O_(2)on Bi/PNC catalysts in flow-cell provides a promising path of electrocatalytic 2e-ORR for practical H_(2)O_(2)production.