Combination of CO_(2) capture using inorganic alkali with subsequently electrochemical conversion of the resultant HCO_(3)^(-)to high-value chemicals is a promising route of low cost and high efficiency.The electroche...Combination of CO_(2) capture using inorganic alkali with subsequently electrochemical conversion of the resultant HCO_(3)^(-)to high-value chemicals is a promising route of low cost and high efficiency.The electrochemical reduction of HCO_(3)^(-)is challenging due to the inaccessible of negatively charged molecular groups to the electrode surface.Herein,we adopt a comprehensive strategy to tackle this challenge,i.e.,cascade of in situ chemical conversion of HCO_(3)^(-)to CO_(2) and CO_(2) electrochemical reduction in a flow cell.With a tailored Ni-N-S single atom catalyst(SACs),where sulfur(S)atoms located in the second shell of Ni center,the CO_(2)electroreduction(CO_(2)ER)to CO is boosted.The experimental results and density functional theory(DFT)calculations reveal that the introduction of S increases the p electron density of N atoms near Ni atom,thereby stabilizing^(*)H over N and boosting the first proton coupled electron transfer process of CO_(2)ER,i.e.,^(*)+e^(-)+^(*)H+^(*)CO_(2)→^(*)COOH.As a result,the obtained catalyst exhibits a high faradaic efficiency(FE_(CO)~98%)and a low overpotential of 425 mV for CO production as well as a superior turnover frequency(TOF)of 47397 h^(-1),outcompeting most of the reported Ni SACs.More importantly,an extremely high FECOof 90%is achieved at 50 mA cm^(-2)in the designed membrane electrode assembly(MEA)cascade electrolyzer fed with liquid bicarbonate.This work not only highlights the significant role of the second coordination on the first coordination shell of the central metal for CO_(2)ER,but also provides an alternative and feasible strategy to realize the electrochemical conversion of HCO_(3)^(-)to high-value chemicals.展开更多
将二氧化碳转化为高附加值的燃料和化学品是缓解当前能源危机和控制温室气体排放的有效策略之一,但此法受限于缺乏高活性与高选择性的电催化剂。因此,我们通过热解含镍金属有机框架结构(MOF)和二氰二胺制得负载高含量镍单原子(7.77%(w)...将二氧化碳转化为高附加值的燃料和化学品是缓解当前能源危机和控制温室气体排放的有效策略之一,但此法受限于缺乏高活性与高选择性的电催化剂。因此,我们通过热解含镍金属有机框架结构(MOF)和二氰二胺制得负载高含量镍单原子(7.77%(w))的超薄氮掺杂二维碳纳米片用于电催化还原CO_(2)生成CO。研究发现高温热解能将MOF中Ni^(2+)转化为Ni^(+)-N-C和Ni^(2+)-N-C结构,且Ni^(+)-N-C含量依赖于热解温度——其含量随热解温度增加呈现火山型变化。800℃下,Ni^(2+)到Ni^(+)-N-C的转化和石墨化的C生成达到最优水平。Ni^(+)-N-C结构有适宜的^(*)CO中间体结合能,能有效地抑制析氢反应的同时还能促进CO生成。因此,800℃热处理制得的材料(Ni-N-C-800)催化CO_(2)生成CO效率最高。调节电解液浓度,能进一步优化电催化性能。当电解液(碳酸氢钾)浓度为0.5 mol·L^(−1)时,Ni-N-C-800的CO生成选择性在较宽电压窗口内(−0.77到^(−1).07 V vs.RHE)都高于90%,且具有优良的稳定性。这些结果表明,选择合适的前躯体通过调控热解温度以及氮掺杂可以有效提高镍基MOF衍生催化剂的二氧化碳电催化性能。展开更多
研究了硬质合金表面Ni P 纳米Ti(C,N)化学复合镀工艺以及热处理对复合镀层性能影响的规律。结果表-);2)较好的明:1)施镀工艺中各因素对镀速影响的显著性顺序是:温度→pH值→纳米Ti(C,N)加入量→χ(Ni2+ H2PO2施镀工艺为:28g L氯化镍、... 研究了硬质合金表面Ni P 纳米Ti(C,N)化学复合镀工艺以及热处理对复合镀层性能影响的规律。结果表-);2)较好的明:1)施镀工艺中各因素对镀速影响的显著性顺序是:温度→pH值→纳米Ti(C,N)加入量→χ(Ni2+ H2PO2施镀工艺为:28g L氯化镍、25.76g L次亚磷酸钠,50g L氯化铵、45g L柠檬酸钠,0.001g LPbCl2,6g L纳米Ti(C,N),pH=10,温度为80℃。3)Ni P 纳米Ti(C,N)复合镀层较优的热处理工艺为:在400℃保温150min。采用所推荐的施镀和热处理工艺,获得了硬度是硬质合金基体硬度的2.16倍的Ni P 纳米Ti(C,N)复合镀层。并对以上结果产生的原因进行了简单讨论。展开更多
Fine-tuning of the coordination environment of single-atom catalysts(SACs)is effective to optimize their catalytic performances,yet it remains challenging due to the vulnerability of SACs.Herein,we report a new approa...Fine-tuning of the coordination environment of single-atom catalysts(SACs)is effective to optimize their catalytic performances,yet it remains challenging due to the vulnerability of SACs.Herein,we report a new approach to engineering the coordination environment of M-N-C(M=Fe,Co,and Ni)SACs by using glutamic acid as the N/C source and pyrolysis atmosphere as a regulator.Compared with that in N2,NH3 was able to promote the doping of N at 7<700℃yet etch the N-species at higher temperatures,by which the M-N coordination number(CN)and the electronic structure were delicately tuned.It was found that the electron density of Ni single atoms increased with the decrease of Ni-N CN.As a consequence,the capability of Ni-N-C to dissociate H2 was greatly enhanced and a higher catalytic activity in chemoselective hydrogenation of functionalized nitroarenes was achieved.Moreover,this modulation method could be applied to other transition metals including Fe and Co.In particular,the as-synthesized Co-N-C SAC afforded a turnover frequency of 152.3 h~1 with 99%selectivity to 3-vinylaniline in the hydrogenation of 3-nitrostyrene,which was the highest ever reported thus far and was at least one order of magnitude more active than state-of-the-art noble-metal-free M-N-C catalysts,demonstrating the great potential of engineering the coordination environment of SACs.展开更多
基金financially supported by the Natural Science Foundation of Shandong Province (ZR2020QB132,ZR2020MB025)the Opening Project of State Key Laboratory of High Performance Ceramics and Superfine Microstructure (SKL202108SIC)the Taishan Scholar Program of Shandong Province (ts201712046)。
文摘Combination of CO_(2) capture using inorganic alkali with subsequently electrochemical conversion of the resultant HCO_(3)^(-)to high-value chemicals is a promising route of low cost and high efficiency.The electrochemical reduction of HCO_(3)^(-)is challenging due to the inaccessible of negatively charged molecular groups to the electrode surface.Herein,we adopt a comprehensive strategy to tackle this challenge,i.e.,cascade of in situ chemical conversion of HCO_(3)^(-)to CO_(2) and CO_(2) electrochemical reduction in a flow cell.With a tailored Ni-N-S single atom catalyst(SACs),where sulfur(S)atoms located in the second shell of Ni center,the CO_(2)electroreduction(CO_(2)ER)to CO is boosted.The experimental results and density functional theory(DFT)calculations reveal that the introduction of S increases the p electron density of N atoms near Ni atom,thereby stabilizing^(*)H over N and boosting the first proton coupled electron transfer process of CO_(2)ER,i.e.,^(*)+e^(-)+^(*)H+^(*)CO_(2)→^(*)COOH.As a result,the obtained catalyst exhibits a high faradaic efficiency(FE_(CO)~98%)and a low overpotential of 425 mV for CO production as well as a superior turnover frequency(TOF)of 47397 h^(-1),outcompeting most of the reported Ni SACs.More importantly,an extremely high FECOof 90%is achieved at 50 mA cm^(-2)in the designed membrane electrode assembly(MEA)cascade electrolyzer fed with liquid bicarbonate.This work not only highlights the significant role of the second coordination on the first coordination shell of the central metal for CO_(2)ER,but also provides an alternative and feasible strategy to realize the electrochemical conversion of HCO_(3)^(-)to high-value chemicals.
文摘将二氧化碳转化为高附加值的燃料和化学品是缓解当前能源危机和控制温室气体排放的有效策略之一,但此法受限于缺乏高活性与高选择性的电催化剂。因此,我们通过热解含镍金属有机框架结构(MOF)和二氰二胺制得负载高含量镍单原子(7.77%(w))的超薄氮掺杂二维碳纳米片用于电催化还原CO_(2)生成CO。研究发现高温热解能将MOF中Ni^(2+)转化为Ni^(+)-N-C和Ni^(2+)-N-C结构,且Ni^(+)-N-C含量依赖于热解温度——其含量随热解温度增加呈现火山型变化。800℃下,Ni^(2+)到Ni^(+)-N-C的转化和石墨化的C生成达到最优水平。Ni^(+)-N-C结构有适宜的^(*)CO中间体结合能,能有效地抑制析氢反应的同时还能促进CO生成。因此,800℃热处理制得的材料(Ni-N-C-800)催化CO_(2)生成CO效率最高。调节电解液浓度,能进一步优化电催化性能。当电解液(碳酸氢钾)浓度为0.5 mol·L^(−1)时,Ni-N-C-800的CO生成选择性在较宽电压窗口内(−0.77到^(−1).07 V vs.RHE)都高于90%,且具有优良的稳定性。这些结果表明,选择合适的前躯体通过调控热解温度以及氮掺杂可以有效提高镍基MOF衍生催化剂的二氧化碳电催化性能。
文摘研究了Al2O3/Ti(C,N)-Ni-Ti陶瓷复合刀具对淬硬35CrMo合金钢进行连续干切削时各切削参数对切削力的影响.结果表明:切削深度对切削力的影响最显著,切削速度的影响最小.对比研究了Al2O3/Ti(C,N)和Al2O3/Ti(C,N)-Ni-Ti陶瓷刀具的耐磨性能和磨损形态:后者的耐磨性能明显优于前者,其中Al2O3/Ti(C,N)-5%(Ni,Ti)的耐磨性能最高.Al2O3/Ti(C,N)-Ni-Ti刀具的磨损形态主要表现为后刀面的磨粒磨损和疲劳磨损,由于这种材料具有较高的弯曲强度和断裂韧性,能有效防止前刀面出现崩刃破损现象,因此具有较高的可靠性,适用于高速切削.在高速切削条件(ap=0.06 mm,vc=254.9 m/min,vf=0.09 mm/r)下,Al2O3/Ti(C,N)-5%(Ni,Ti)刀具的切削耐用度为150 min.
文摘 研究了硬质合金表面Ni P 纳米Ti(C,N)化学复合镀工艺以及热处理对复合镀层性能影响的规律。结果表-);2)较好的明:1)施镀工艺中各因素对镀速影响的显著性顺序是:温度→pH值→纳米Ti(C,N)加入量→χ(Ni2+ H2PO2施镀工艺为:28g L氯化镍、25.76g L次亚磷酸钠,50g L氯化铵、45g L柠檬酸钠,0.001g LPbCl2,6g L纳米Ti(C,N),pH=10,温度为80℃。3)Ni P 纳米Ti(C,N)复合镀层较优的热处理工艺为:在400℃保温150min。采用所推荐的施镀和热处理工艺,获得了硬度是硬质合金基体硬度的2.16倍的Ni P 纳米Ti(C,N)复合镀层。并对以上结果产生的原因进行了简单讨论。
基金supported by the National Key Technology R&D Program of China(No.2020YFA0710202)the National Natural Science Foundation of China(Nos.U1662130,21690080,21690084,and 21721004)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB17020100)。
文摘Fine-tuning of the coordination environment of single-atom catalysts(SACs)is effective to optimize their catalytic performances,yet it remains challenging due to the vulnerability of SACs.Herein,we report a new approach to engineering the coordination environment of M-N-C(M=Fe,Co,and Ni)SACs by using glutamic acid as the N/C source and pyrolysis atmosphere as a regulator.Compared with that in N2,NH3 was able to promote the doping of N at 7<700℃yet etch the N-species at higher temperatures,by which the M-N coordination number(CN)and the electronic structure were delicately tuned.It was found that the electron density of Ni single atoms increased with the decrease of Ni-N CN.As a consequence,the capability of Ni-N-C to dissociate H2 was greatly enhanced and a higher catalytic activity in chemoselective hydrogenation of functionalized nitroarenes was achieved.Moreover,this modulation method could be applied to other transition metals including Fe and Co.In particular,the as-synthesized Co-N-C SAC afforded a turnover frequency of 152.3 h~1 with 99%selectivity to 3-vinylaniline in the hydrogenation of 3-nitrostyrene,which was the highest ever reported thus far and was at least one order of magnitude more active than state-of-the-art noble-metal-free M-N-C catalysts,demonstrating the great potential of engineering the coordination environment of SACs.
