Reducing a Pt loading with improved power output and durability is essential to promote the large-scale application of proton exchange membrane fuel cells(PEMFCs).To achieve this goal,constructing optimized structure ...Reducing a Pt loading with improved power output and durability is essential to promote the large-scale application of proton exchange membrane fuel cells(PEMFCs).To achieve this goal,constructing optimized structure of catalyst layers with efficient mass transportation channels plays a vital role.Herein,PEMFCs with order-structured cathodic electrodes were fabricated by depositing Pt nanoparticles by Ebeam onto vertically aligned carbon nanotubes(VACNTs)growth on Al foil via plasma-enhanced chemical vapor deposition.Results demonstrate that the proportion of hydrophilic Pt-deposited region along VACNTs and residual hydrophobic region of VANCTs without Pt strongly influences the cell performance,in particular at high current densities.When Pt nanoparticles deposit on the top depth of around 600 nm on VACNTs with a length of 4.6μm,the cell shows the highest performance,compared with others with various lengths of VACNTs.It delivers a maximum power output of 1.61 W cm^(-2)(H_(2)/O_(2),150 k Pa)and 0.79 W cm^(-2)(H_(2)/Air,150 k Pa)at Pt loading of 50μg cm^(-2),exceeding most of previously reported PEMFCs with Pt loading of<100μg cm^(-2).Even though the Pt loading is down to 30μg cm^(-2)(1.36 W cm^(-2)),the performance is also better than 100μg cm^(-2)(1.24 W cm^(-2))of commercial Pt/C,and presents better stability.This excellent performance is critical attributed to the ordered hydrophobic region providing sufficient mass passages to facilitate the fast water drainage at high current densities.This work gives a new understanding for oxygen reduction reaction occurred in VACNTs-based ordered electrodes,demonstrating the most possibility to achieve a substantial reduction in Pt loading<100μg cm^(-2) without sacrificing in performance.展开更多
To improve performance of membrane electrode assembly(MEA)at large current density region,efficient mass transfer at the cathode is desired,for which a feasible strategy is to lower catalyst layer thickness by constru...To improve performance of membrane electrode assembly(MEA)at large current density region,efficient mass transfer at the cathode is desired,for which a feasible strategy is to lower catalyst layer thickness by constructing high loading Pt-alloy catalysts on carbon.But the high loading may induce unwanted par-ticle aggregation.In this work,H-PtNi/C with 33%(mass)Pt loading on carbon and monodisperse distri-bution of 3.55 nm PtNi nanoparticles,was prepared by a bimodal-pore route.In electrocatalytic oxygen reduction reaction(ORR),H-PtNi/C displays an activity inferior to the low Pt loading catalyst L-PtNi/C(13.3%(mass))in the half-cell.While in H_(2)-0_(2) MEA,H-PtNi/C delivers the peak power density of 1.51 W·cm^(-2) and the mass transfer limiting current density of 4.4 A·cm^(-2),being 21%and 16%higher than those of L-PtNi/C(1.25 W·cm^(-2),3.8 A·cm^(-2))respectively,which can be ascribed to enhanced mass trans-fer brought by the thinner catalyst layer in the former.In addition,the same method can be used to pre-pare PtFe alloy catalyst with a high-Pt loading of 36%(mass).This work may lead to a range of catalyst materials for the large current density applications,such as fuel cell vehicles.展开更多
Aiming at purification of NO_(x)from hydrogen internal combustion engines(HICEs),the hydrogen selective catalytic reduction(H_(2)-SCR)reaction was investigated over a series of Pt/KFI zeolite catalysts.H_(2)can readil...Aiming at purification of NO_(x)from hydrogen internal combustion engines(HICEs),the hydrogen selective catalytic reduction(H_(2)-SCR)reaction was investigated over a series of Pt/KFI zeolite catalysts.H_(2)can readily reduce NO_(x)to N_(2)and N_(2)O while O_(2)inhibited the deNO_(x)efficiency by consuming the reductant H_(2).The Pt/KFI zeolite catalysts with Pt loading below 0.1wt.% are optimized H_(2)-SCR catalysts due to its suitable operation temperature window since high Pt loading favors the H_(2)-O_(2)reaction which lead to the insufficient of reactants.Compared to metal Pt^(0)species,Pt^(δ+)species showed lower activation energy of H_(2)-SCR reaction and thought to be as reasonable active sites.Further,Eley-Rideal(E-R)reaction mechanism was proposed as evidenced by the reaction orders in kinetic studies.Last,the optimized reactor was designed with hybrid Pt/KFI catalysts with various Pt loading which achieve a high NO_(x)conversion in a wide temperature range.展开更多
Highly efficient catalysts for electrolysis of water are crucial to the development of hydrogen energy which is helpful to carbon neutralization.Recently,high temperature shock(HTS),with advantage of rapid speed,unive...Highly efficient catalysts for electrolysis of water are crucial to the development of hydrogen energy which is helpful to carbon neutralization.Recently,high temperature shock(HTS),with advantage of rapid speed,universality and scalable production,has been a promising method in synthesis of nanomaterials.In this paper,HST was used to treat low Pt loading Mo_(6)S_(8)for enhanced water splitting performance.Impressively,the optimized MoS_(2)/MoO_(2)/Mo_(6)S_(8)nano-composite with low Pt mass loading(~4%)displays well hydrogen evolution reaction(HER)electrochemical performance.The overpotential is 124 mV to reach 10 mA/cm^(2)and the corresponding Tafel slope is 88 mV/dec in acidic electrolyte.Its mass activity is 6.2 mA/μg_(Pt)at-124 mV vs.RHE,which is almost 2 times relative to 20%Pt/C.Moreover,it presents distinguished stability even after 2000 cycles.This work will broaden the way of catalysts preparation and the application of hydrogen evolution.展开更多
The catalyst layers(CLs) electrode is the key component of the membrane electrode assembly(MEA) in proton exchange membrane fuel cells(PEMFCs). Conventional electrodes for PEMFCs are composed of carbon-supported, iono...The catalyst layers(CLs) electrode is the key component of the membrane electrode assembly(MEA) in proton exchange membrane fuel cells(PEMFCs). Conventional electrodes for PEMFCs are composed of carbon-supported, ionomer, and Pt nanoparticles, all immersed together and sprayed with a micron-level thickness of CLs. They have a performance trade-off where increasing the Pt loading leads to higher performance of abundant triple-phase boundary areas but increases the electrode cost. Major challenges must be overcome before realizing its wide commercialization. Literature research revealed that it is impossible to achieve performance and durability targets with only high-performance catalysts, so the controllable design of CLs architecture in MEAs for PEMFCs must now be the top priority to meet industry goals. From this perspective, a 3D ordered electrode circumvents this issue with a support-free architecture and ultrathin thickness while reducing noble metal Pt loadings. Herein, we discuss the motivation in-depth and summarize the necessary CLs structural features for designing ultralow Pt loading electrodes. Critical issues that remain in progress for 3D ordered CLs must be studied and characterized. Furthermore, approaches for 3D ordered CLs architecture electrode development, involving material design, structure optimization, preparation technology, and characterization techniques, are summarized and are expected to be next-generation CLs for PEMFCs. Finally, the review concludes with perspectives on possible research directions of CL architecture to address the significant challenges in the future.展开更多
Improving the performance of proton exchange membrane fuel cells(PEMFCs)requires deep understanding of the reac-tive transport processes inside the catalyst layers(CLs).In this study,a particle-overlapping model is de...Improving the performance of proton exchange membrane fuel cells(PEMFCs)requires deep understanding of the reac-tive transport processes inside the catalyst layers(CLs).In this study,a particle-overlapping model is developed for accu-rately describing the hierarchical structures and oxygen reactive transport processes in CLs.The analytical solutions derived from this model indicate that carbon particle overlap increases ionomer thickness,reduces specific surface areas of ionomer and carbon,and further intensifies the local oxygen transport resistance(R_(other)).The relationship between Rother and roughness factor predicted by the model in the range of 800-1600 sm^(-1) agrees well with the experiments.Then,a multiscale model is developed by coupling the particle-overlapping model with cell-scale models,which is validated by comparing with the polarization curves and local current density distribution obtained in experiments.The relative error of local current density distribution is below 15%in the ohmic polarization region.Finally,the multiscale model is employed to explore effects of CL structural parameters including Pt loading,I/C,ionomer coverage and carbon particle radius on the cell performance as well as the phase-change-induced(PCI)flow and capillary-driven(CD)flow in CL.The result demonstrates that the CL structural parameters have significant effects on the cell performance as well as the PCI and CD flows.Optimizing the CL structure can increase the current density and further enhance the heat-pipe effect within the CL,leading to overall higher PCI and CD rates.The maximum increase of PCI and CD rates can exceed 145%.Besides,the enhanced heat-pipe effect causes the reverse flow regions of PCI and CD near the CL/PEM interface,which can occupy about 30%of the CL.The multiscale model significantly contributes to a deep understanding of reactive trans-port and multiphase heat transfer processes inside PEMFCs.展开更多
基金finically supported by the National Natural Science Foundation of China(22075055)the Guangxi Science and Technology Project(AB16380030)the Innovation Project of Guangxi Graduate Education(YCSW2020052)。
文摘Reducing a Pt loading with improved power output and durability is essential to promote the large-scale application of proton exchange membrane fuel cells(PEMFCs).To achieve this goal,constructing optimized structure of catalyst layers with efficient mass transportation channels plays a vital role.Herein,PEMFCs with order-structured cathodic electrodes were fabricated by depositing Pt nanoparticles by Ebeam onto vertically aligned carbon nanotubes(VACNTs)growth on Al foil via plasma-enhanced chemical vapor deposition.Results demonstrate that the proportion of hydrophilic Pt-deposited region along VACNTs and residual hydrophobic region of VANCTs without Pt strongly influences the cell performance,in particular at high current densities.When Pt nanoparticles deposit on the top depth of around 600 nm on VACNTs with a length of 4.6μm,the cell shows the highest performance,compared with others with various lengths of VACNTs.It delivers a maximum power output of 1.61 W cm^(-2)(H_(2)/O_(2),150 k Pa)and 0.79 W cm^(-2)(H_(2)/Air,150 k Pa)at Pt loading of 50μg cm^(-2),exceeding most of previously reported PEMFCs with Pt loading of<100μg cm^(-2).Even though the Pt loading is down to 30μg cm^(-2)(1.36 W cm^(-2)),the performance is also better than 100μg cm^(-2)(1.24 W cm^(-2))of commercial Pt/C,and presents better stability.This excellent performance is critical attributed to the ordered hydrophobic region providing sufficient mass passages to facilitate the fast water drainage at high current densities.This work gives a new understanding for oxygen reduction reaction occurred in VACNTs-based ordered electrodes,demonstrating the most possibility to achieve a substantial reduction in Pt loading<100μg cm^(-2) without sacrificing in performance.
基金financially supported by the National Key Research and Development Program of China (2019YFB1504503)the National Natural Science Foundation of China (21878030 and 21761162015)
文摘To improve performance of membrane electrode assembly(MEA)at large current density region,efficient mass transfer at the cathode is desired,for which a feasible strategy is to lower catalyst layer thickness by constructing high loading Pt-alloy catalysts on carbon.But the high loading may induce unwanted par-ticle aggregation.In this work,H-PtNi/C with 33%(mass)Pt loading on carbon and monodisperse distri-bution of 3.55 nm PtNi nanoparticles,was prepared by a bimodal-pore route.In electrocatalytic oxygen reduction reaction(ORR),H-PtNi/C displays an activity inferior to the low Pt loading catalyst L-PtNi/C(13.3%(mass))in the half-cell.While in H_(2)-0_(2) MEA,H-PtNi/C delivers the peak power density of 1.51 W·cm^(-2) and the mass transfer limiting current density of 4.4 A·cm^(-2),being 21%and 16%higher than those of L-PtNi/C(1.25 W·cm^(-2),3.8 A·cm^(-2))respectively,which can be ascribed to enhanced mass trans-fer brought by the thinner catalyst layer in the former.In addition,the same method can be used to pre-pare PtFe alloy catalyst with a high-Pt loading of 36%(mass).This work may lead to a range of catalyst materials for the large current density applications,such as fuel cell vehicles.
基金supported by the National Natural Science Foundation of China(Nos.21906172 and 22188102)the Special project of eco-environmental technology for peak carbon dioxide emissions and carbon neutrality(No.RCEES-TDZ-2021-2)。
文摘Aiming at purification of NO_(x)from hydrogen internal combustion engines(HICEs),the hydrogen selective catalytic reduction(H_(2)-SCR)reaction was investigated over a series of Pt/KFI zeolite catalysts.H_(2)can readily reduce NO_(x)to N_(2)and N_(2)O while O_(2)inhibited the deNO_(x)efficiency by consuming the reductant H_(2).The Pt/KFI zeolite catalysts with Pt loading below 0.1wt.% are optimized H_(2)-SCR catalysts due to its suitable operation temperature window since high Pt loading favors the H_(2)-O_(2)reaction which lead to the insufficient of reactants.Compared to metal Pt^(0)species,Pt^(δ+)species showed lower activation energy of H_(2)-SCR reaction and thought to be as reasonable active sites.Further,Eley-Rideal(E-R)reaction mechanism was proposed as evidenced by the reaction orders in kinetic studies.Last,the optimized reactor was designed with hybrid Pt/KFI catalysts with various Pt loading which achieve a high NO_(x)conversion in a wide temperature range.
基金supported by Beijing Natural Science Foundation(No.2232062)National Natural Science Foundation of China(No.21875223)。
文摘Highly efficient catalysts for electrolysis of water are crucial to the development of hydrogen energy which is helpful to carbon neutralization.Recently,high temperature shock(HTS),with advantage of rapid speed,universality and scalable production,has been a promising method in synthesis of nanomaterials.In this paper,HST was used to treat low Pt loading Mo_(6)S_(8)for enhanced water splitting performance.Impressively,the optimized MoS_(2)/MoO_(2)/Mo_(6)S_(8)nano-composite with low Pt mass loading(~4%)displays well hydrogen evolution reaction(HER)electrochemical performance.The overpotential is 124 mV to reach 10 mA/cm^(2)and the corresponding Tafel slope is 88 mV/dec in acidic electrolyte.Its mass activity is 6.2 mA/μg_(Pt)at-124 mV vs.RHE,which is almost 2 times relative to 20%Pt/C.Moreover,it presents distinguished stability even after 2000 cycles.This work will broaden the way of catalysts preparation and the application of hydrogen evolution.
基金funded by the Natural Science Foundation of Shandong Province, China (ZR2023MB049)the China Postdoctoral Science Foundation (2020M670483)the Science Foundation of Weifang University (2023BS11)。
文摘The catalyst layers(CLs) electrode is the key component of the membrane electrode assembly(MEA) in proton exchange membrane fuel cells(PEMFCs). Conventional electrodes for PEMFCs are composed of carbon-supported, ionomer, and Pt nanoparticles, all immersed together and sprayed with a micron-level thickness of CLs. They have a performance trade-off where increasing the Pt loading leads to higher performance of abundant triple-phase boundary areas but increases the electrode cost. Major challenges must be overcome before realizing its wide commercialization. Literature research revealed that it is impossible to achieve performance and durability targets with only high-performance catalysts, so the controllable design of CLs architecture in MEAs for PEMFCs must now be the top priority to meet industry goals. From this perspective, a 3D ordered electrode circumvents this issue with a support-free architecture and ultrathin thickness while reducing noble metal Pt loadings. Herein, we discuss the motivation in-depth and summarize the necessary CLs structural features for designing ultralow Pt loading electrodes. Critical issues that remain in progress for 3D ordered CLs must be studied and characterized. Furthermore, approaches for 3D ordered CLs architecture electrode development, involving material design, structure optimization, preparation technology, and characterization techniques, are summarized and are expected to be next-generation CLs for PEMFCs. Finally, the review concludes with perspectives on possible research directions of CL architecture to address the significant challenges in the future.
基金supported by the National Key Research and Development Program(2021YFB4001701)National Nature Science Foundation of China(52376074)the Fundamental Research Funds for the Central Universities.
文摘Improving the performance of proton exchange membrane fuel cells(PEMFCs)requires deep understanding of the reac-tive transport processes inside the catalyst layers(CLs).In this study,a particle-overlapping model is developed for accu-rately describing the hierarchical structures and oxygen reactive transport processes in CLs.The analytical solutions derived from this model indicate that carbon particle overlap increases ionomer thickness,reduces specific surface areas of ionomer and carbon,and further intensifies the local oxygen transport resistance(R_(other)).The relationship between Rother and roughness factor predicted by the model in the range of 800-1600 sm^(-1) agrees well with the experiments.Then,a multiscale model is developed by coupling the particle-overlapping model with cell-scale models,which is validated by comparing with the polarization curves and local current density distribution obtained in experiments.The relative error of local current density distribution is below 15%in the ohmic polarization region.Finally,the multiscale model is employed to explore effects of CL structural parameters including Pt loading,I/C,ionomer coverage and carbon particle radius on the cell performance as well as the phase-change-induced(PCI)flow and capillary-driven(CD)flow in CL.The result demonstrates that the CL structural parameters have significant effects on the cell performance as well as the PCI and CD flows.Optimizing the CL structure can increase the current density and further enhance the heat-pipe effect within the CL,leading to overall higher PCI and CD rates.The maximum increase of PCI and CD rates can exceed 145%.Besides,the enhanced heat-pipe effect causes the reverse flow regions of PCI and CD near the CL/PEM interface,which can occupy about 30%of the CL.The multiscale model significantly contributes to a deep understanding of reactive trans-port and multiphase heat transfer processes inside PEMFCs.
