The Experts below are selected from a list of 36966 Experts worldwide ranked by ideXlab platform
Stephen M. Ansell - One of the best experts on this subject based on the ideXlab platform.
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germinal center b GCB and non GCB cell like diffuse large b cell lymphomas have similar outcomes following autologous haematopoietic stem cell transplantation
British Journal of Haematology, 2008Co-Authors: Luciano J. Costa, Andrew L. Feldman, Ivana N. Micallef, David J. Inwards, Patrick B. Johnston, Luis F. Porrata, Stephen M. AnsellAbstract:Patients with germinal center B cell-like (GCB) and non-GCB diffuse large B cell lymphomas (DLBCL) receiving first line therapy have distinct prognosis. We explored the differences in outcome following salvage autologous hematopoietic stem cell (HSC) transplantation between patients with GCB and non-GCB DLBCL. Forty-four patients with relapsed and 15 patients with primary refractory chemosensitive disease undergoing BEAM (BCNU [carmustine], etoposide, cytarabine, melphalan) conditioning and autologous HSC were included. Immunohistochemical analysis was performed for CD10, BCL-6, MUM1 (allowing classification into GCB and non-GCB-like DLBCL) and BCL-2. Median follow-up of survivors was 25 months; median age at the time of transplantation was 60 years (range 17-77). Thirty-two patients (54%) were classified as having GCB and 27 (46%) as having non-GCB-like DLBCL. Patients with GCB and non-GCB DLBCL did not differ in the risk of progression after HSC transplant (P = 0.78) or overall survival (P = 0.48). In multivariate analysis, only time to progression after initial treatment impacted overall survival. We conclude that patients with relapsed or primary refractory chemosensitive GCB and non-GCB-like DLBCL derive similar benefit from autologous HSC transplant.
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Germinal center B (GCB) and non‐GCB cell‐like diffuse large B cell lymphomas have similar outcomes following autologous haematopoietic stem cell transplantation
British journal of haematology, 2008Co-Authors: Luciano J. Costa, Andrew L. Feldman, Ivana N. Micallef, David J. Inwards, Patrick B. Johnston, Luis F. Porrata, Stephen M. AnsellAbstract:Patients with germinal center B cell-like (GCB) and non-GCB diffuse large B cell lymphomas (DLBCL) receiving first line therapy have distinct prognosis. We explored the differences in outcome following salvage autologous hematopoietic stem cell (HSC) transplantation between patients with GCB and non-GCB DLBCL. Forty-four patients with relapsed and 15 patients with primary refractory chemosensitive disease undergoing BEAM (BCNU [carmustine], etoposide, cytarabine, melphalan) conditioning and autologous HSC were included. Immunohistochemical analysis was performed for CD10, BCL-6, MUM1 (allowing classification into GCB and non-GCB-like DLBCL) and BCL-2. Median follow-up of survivors was 25 months; median age at the time of transplantation was 60 years (range 17-77). Thirty-two patients (54%) were classified as having GCB and 27 (46%) as having non-GCB-like DLBCL. Patients with GCB and non-GCB DLBCL did not differ in the risk of progression after HSC transplant (P = 0.78) or overall survival (P = 0.48). In multivariate analysis, only time to progression after initial treatment impacted overall survival. We conclude that patients with relapsed or primary refractory chemosensitive GCB and non-GCB-like DLBCL derive similar benefit from autologous HSC transplant.
Gerwin Huls - One of the best experts on this subject based on the ideXlab platform.
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cd47 expression defines efficacy of rituximab with chop in non germinal center b cell non GCB diffuse large b cell lymphoma patients dlbcl but not in GCB dlbcl
Cancer immunology research, 2019Co-Authors: Renee Bouwstra, Hilde A M Kooistra, Rudolf S. N. Fehrmann, Emanuele Ammatuna, Gerwin Huls, Janneke Willemien De Boer, Ewa Cendrowicz, Christine Eulenburg, Marcel Nijland, Edwin BremerAbstract:Addition of rituximab (R) to "CHOP" (cyclophosphamide, doxorubicin, vincristine, and prednisone) chemotherapy improved outcome for diffuse large B-cell lymphoma (DLBCL) patients. Approximately 40% of patients who receive R-CHOP still succumb to disease due to intrinsic resistance or relapse. A potential negative regulator of DLBCL treatment outcome is the CD47 "don't eat me" immune checkpoint. To delineate the impact of CD47, we used a clinically and molecularly well-annotated cohort of 939 DLBCL patients, comprising both germinal center B-cell (GCB) and non-GCB DLBCL subtypes, treated with either CHOP or R-CHOP. High (above median) CD47 mRNA expression correlated with a detrimental effect on overall survival (OS) when DLBCL patients received R-CHOP therapy (P = 0.001), but not CHOP therapy (P = 0.645). Accordingly, patients with low CD47 expression benefited most from the addition of rituximab to CHOP [HR, 0.32; confidence interval (CI), 0.21-0.50; P < 0.001]. This negative impact of high CD47 expression on OS after R-CHOP treatment was only evident in cancers of non-GCB origin (HR, 2.09; CI, 1.26-3.47; P = 0.004) and not in the GCB subtype (HR, 1.16; CI, 0.68-1.99; P = 0.58). This differential impact of CD47 in non-GCB and GCB was confirmed in vitro, as macrophage-mediated phagocytosis stimulated by rituximab was augmented by CD47-blocking antibody only in non-GCB cell lines. Thus, high expression of CD47 mRNA limited the benefit of addition of rituximab to CHOP in non-GCB patients, and CD47-blockade only augmented rituximab-mediated phagocytosis in non-GCB cell lines. Patients with non-GCB DLBCL may benefit from CD47-targeted therapy in addition to rituximab.
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CD47 Expression Defines Efficacy of Rituximab with CHOP in Non–Germinal Center B-cell (Non-GCB) Diffuse Large B-cell Lymphoma Patients (DLBCL), but Not in GCB DLBCL
Cancer immunology research, 2019Co-Authors: Renee Bouwstra, Hilde A M Kooistra, Rudolf S. N. Fehrmann, Emanuele Ammatuna, Janneke Willemien De Boer, Ewa Cendrowicz, Christine Eulenburg, Marcel Nijland, Gerwin HulsAbstract:Addition of rituximab (R) to "CHOP" (cyclophosphamide, doxorubicin, vincristine, and prednisone) chemotherapy improved outcome for diffuse large B-cell lymphoma (DLBCL) patients. Approximately 40% of patients who receive R-CHOP still succumb to disease due to intrinsic resistance or relapse. A potential negative regulator of DLBCL treatment outcome is the CD47 "don't eat me" immune checkpoint. To delineate the impact of CD47, we used a clinically and molecularly well-annotated cohort of 939 DLBCL patients, comprising both germinal center B-cell (GCB) and non-GCB DLBCL subtypes, treated with either CHOP or R-CHOP. High (above median) CD47 mRNA expression correlated with a detrimental effect on overall survival (OS) when DLBCL patients received R-CHOP therapy (P = 0.001), but not CHOP therapy (P = 0.645). Accordingly, patients with low CD47 expression benefited most from the addition of rituximab to CHOP [HR, 0.32; confidence interval (CI), 0.21-0.50; P < 0.001]. This negative impact of high CD47 expression on OS after R-CHOP treatment was only evident in cancers of non-GCB origin (HR, 2.09; CI, 1.26-3.47; P = 0.004) and not in the GCB subtype (HR, 1.16; CI, 0.68-1.99; P = 0.58). This differential impact of CD47 in non-GCB and GCB was confirmed in vitro, as macrophage-mediated phagocytosis stimulated by rituximab was augmented by CD47-blocking antibody only in non-GCB cell lines. Thus, high expression of CD47 mRNA limited the benefit of addition of rituximab to CHOP in non-GCB patients, and CD47-blockade only augmented rituximab-mediated phagocytosis in non-GCB cell lines. Patients with non-GCB DLBCL may benefit from CD47-targeted therapy in addition to rituximab.
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CD47 Expression Defines the Efficacy of Rituximab in Non-Germinal Center B-Cell (non-GCB) Diffuse Large B-Cell Lymphoma (DLBCL)
Blood, 2018Co-Authors: Tom Van Meerten, Renee Bouwstra, De Boer Janneke, Hilde A M Kooistra, Rudolf S. N. Fehrmann, Emanuele Ammatuna, Gerwin Huls, Edwin BremerAbstract:CD47 is an immune-checkpoint protein that binds SIRPa on immune cells to deliver an inhibitory "don9t eat me" signal. CD47 is a prominent new target in B-cell malignancies, in which CD47 antibody in combination with the CD20 antibody rituximab (R) is explored in clinical trials. Addition of R to CHOP chemotherapy significantly improves survival of patients with DLBCL, but how CD47 expression contributes to this positive impact of R on patient outcome is currently unclear. Especially in the context of the different cell-of-origin DLBCL subtypes (Germinal Center B-cell (GCB) vs non-GCB DLBCL). We therefore investigated the impact of CD47 expression on rituximab efficacy. We first studied a clinically well annotated transcriptome cohort of 939 DLBCL patients treated with either CHOP or R-CHOP, and we validated these findings in functional in vitro assays. Our analyses showed that overall survival (OS) for patients with high CD47 expression (i.e. above median) is worse compared to patients with low CD47 expression (i.e. below median) after R-CHOP (p=0.001), but not after CHOP treatment (p=0.645). Correspondingly, patients with low CD47 expression benefited most from addition of R to CHOP (HR=0.32, CI:[0.21-0.50], p We further investigated this differential impact of CD47 in non-GCB and GCB subtypes in vitro. Non-GCB and GCB DLBCL cell lines (n=6) were mixed with allogeneic M1 macrophages and treated with a CD47 blocking antibody, which comprises human IgG4. Results confirmed that macrophage-mediated phagocytosis by R was augmented with CD47-blocking antibody only in non-GCB DLBCL cell lines, and not in GCB DLBCL cell lines. Also, CD47 blocking co-treatment also increased the number of tumor cells ingested per macrophage, with a clear significant increase in phagocytic index in non-GCB cells, but not in GCB DLBCL cells (p=0.001). In conclusion, the patient benefit of addition of R to CHOP is limited by CD47 specifically in non-GCB patients. In addition, we confirmed that CD47-blocking only augmented rituximab-mediated phagocytosis in non-GCB cell-lines. Together, these data suggest that especially non-GCB DLBCL patients with a currently worse prognosis may benefit from CD47-targeted therapy combined with rituximab. Disclosures No relevant conflicts of interest to declare.
Renee Bouwstra - One of the best experts on this subject based on the ideXlab platform.
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cd47 expression defines efficacy of rituximab with chop in non germinal center b cell non GCB diffuse large b cell lymphoma patients dlbcl but not in GCB dlbcl
Cancer immunology research, 2019Co-Authors: Renee Bouwstra, Hilde A M Kooistra, Rudolf S. N. Fehrmann, Emanuele Ammatuna, Gerwin Huls, Janneke Willemien De Boer, Ewa Cendrowicz, Christine Eulenburg, Marcel Nijland, Edwin BremerAbstract:Addition of rituximab (R) to "CHOP" (cyclophosphamide, doxorubicin, vincristine, and prednisone) chemotherapy improved outcome for diffuse large B-cell lymphoma (DLBCL) patients. Approximately 40% of patients who receive R-CHOP still succumb to disease due to intrinsic resistance or relapse. A potential negative regulator of DLBCL treatment outcome is the CD47 "don't eat me" immune checkpoint. To delineate the impact of CD47, we used a clinically and molecularly well-annotated cohort of 939 DLBCL patients, comprising both germinal center B-cell (GCB) and non-GCB DLBCL subtypes, treated with either CHOP or R-CHOP. High (above median) CD47 mRNA expression correlated with a detrimental effect on overall survival (OS) when DLBCL patients received R-CHOP therapy (P = 0.001), but not CHOP therapy (P = 0.645). Accordingly, patients with low CD47 expression benefited most from the addition of rituximab to CHOP [HR, 0.32; confidence interval (CI), 0.21-0.50; P < 0.001]. This negative impact of high CD47 expression on OS after R-CHOP treatment was only evident in cancers of non-GCB origin (HR, 2.09; CI, 1.26-3.47; P = 0.004) and not in the GCB subtype (HR, 1.16; CI, 0.68-1.99; P = 0.58). This differential impact of CD47 in non-GCB and GCB was confirmed in vitro, as macrophage-mediated phagocytosis stimulated by rituximab was augmented by CD47-blocking antibody only in non-GCB cell lines. Thus, high expression of CD47 mRNA limited the benefit of addition of rituximab to CHOP in non-GCB patients, and CD47-blockade only augmented rituximab-mediated phagocytosis in non-GCB cell lines. Patients with non-GCB DLBCL may benefit from CD47-targeted therapy in addition to rituximab.
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CD47 Expression Defines Efficacy of Rituximab with CHOP in Non–Germinal Center B-cell (Non-GCB) Diffuse Large B-cell Lymphoma Patients (DLBCL), but Not in GCB DLBCL
Cancer immunology research, 2019Co-Authors: Renee Bouwstra, Hilde A M Kooistra, Rudolf S. N. Fehrmann, Emanuele Ammatuna, Janneke Willemien De Boer, Ewa Cendrowicz, Christine Eulenburg, Marcel Nijland, Gerwin HulsAbstract:Addition of rituximab (R) to "CHOP" (cyclophosphamide, doxorubicin, vincristine, and prednisone) chemotherapy improved outcome for diffuse large B-cell lymphoma (DLBCL) patients. Approximately 40% of patients who receive R-CHOP still succumb to disease due to intrinsic resistance or relapse. A potential negative regulator of DLBCL treatment outcome is the CD47 "don't eat me" immune checkpoint. To delineate the impact of CD47, we used a clinically and molecularly well-annotated cohort of 939 DLBCL patients, comprising both germinal center B-cell (GCB) and non-GCB DLBCL subtypes, treated with either CHOP or R-CHOP. High (above median) CD47 mRNA expression correlated with a detrimental effect on overall survival (OS) when DLBCL patients received R-CHOP therapy (P = 0.001), but not CHOP therapy (P = 0.645). Accordingly, patients with low CD47 expression benefited most from the addition of rituximab to CHOP [HR, 0.32; confidence interval (CI), 0.21-0.50; P < 0.001]. This negative impact of high CD47 expression on OS after R-CHOP treatment was only evident in cancers of non-GCB origin (HR, 2.09; CI, 1.26-3.47; P = 0.004) and not in the GCB subtype (HR, 1.16; CI, 0.68-1.99; P = 0.58). This differential impact of CD47 in non-GCB and GCB was confirmed in vitro, as macrophage-mediated phagocytosis stimulated by rituximab was augmented by CD47-blocking antibody only in non-GCB cell lines. Thus, high expression of CD47 mRNA limited the benefit of addition of rituximab to CHOP in non-GCB patients, and CD47-blockade only augmented rituximab-mediated phagocytosis in non-GCB cell lines. Patients with non-GCB DLBCL may benefit from CD47-targeted therapy in addition to rituximab.
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CD47 Expression Defines the Efficacy of Rituximab in Non-Germinal Center B-Cell (non-GCB) Diffuse Large B-Cell Lymphoma (DLBCL)
Blood, 2018Co-Authors: Tom Van Meerten, Renee Bouwstra, De Boer Janneke, Hilde A M Kooistra, Rudolf S. N. Fehrmann, Emanuele Ammatuna, Gerwin Huls, Edwin BremerAbstract:CD47 is an immune-checkpoint protein that binds SIRPa on immune cells to deliver an inhibitory "don9t eat me" signal. CD47 is a prominent new target in B-cell malignancies, in which CD47 antibody in combination with the CD20 antibody rituximab (R) is explored in clinical trials. Addition of R to CHOP chemotherapy significantly improves survival of patients with DLBCL, but how CD47 expression contributes to this positive impact of R on patient outcome is currently unclear. Especially in the context of the different cell-of-origin DLBCL subtypes (Germinal Center B-cell (GCB) vs non-GCB DLBCL). We therefore investigated the impact of CD47 expression on rituximab efficacy. We first studied a clinically well annotated transcriptome cohort of 939 DLBCL patients treated with either CHOP or R-CHOP, and we validated these findings in functional in vitro assays. Our analyses showed that overall survival (OS) for patients with high CD47 expression (i.e. above median) is worse compared to patients with low CD47 expression (i.e. below median) after R-CHOP (p=0.001), but not after CHOP treatment (p=0.645). Correspondingly, patients with low CD47 expression benefited most from addition of R to CHOP (HR=0.32, CI:[0.21-0.50], p We further investigated this differential impact of CD47 in non-GCB and GCB subtypes in vitro. Non-GCB and GCB DLBCL cell lines (n=6) were mixed with allogeneic M1 macrophages and treated with a CD47 blocking antibody, which comprises human IgG4. Results confirmed that macrophage-mediated phagocytosis by R was augmented with CD47-blocking antibody only in non-GCB DLBCL cell lines, and not in GCB DLBCL cell lines. Also, CD47 blocking co-treatment also increased the number of tumor cells ingested per macrophage, with a clear significant increase in phagocytic index in non-GCB cells, but not in GCB DLBCL cells (p=0.001). In conclusion, the patient benefit of addition of R to CHOP is limited by CD47 specifically in non-GCB patients. In addition, we confirmed that CD47-blocking only augmented rituximab-mediated phagocytosis in non-GCB cell-lines. Together, these data suggest that especially non-GCB DLBCL patients with a currently worse prognosis may benefit from CD47-targeted therapy combined with rituximab. Disclosures No relevant conflicts of interest to declare.
Luciano J. Costa - One of the best experts on this subject based on the ideXlab platform.
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germinal center b GCB and non GCB cell like diffuse large b cell lymphomas have similar outcomes following autologous haematopoietic stem cell transplantation
British Journal of Haematology, 2008Co-Authors: Luciano J. Costa, Andrew L. Feldman, Ivana N. Micallef, David J. Inwards, Patrick B. Johnston, Luis F. Porrata, Stephen M. AnsellAbstract:Patients with germinal center B cell-like (GCB) and non-GCB diffuse large B cell lymphomas (DLBCL) receiving first line therapy have distinct prognosis. We explored the differences in outcome following salvage autologous hematopoietic stem cell (HSC) transplantation between patients with GCB and non-GCB DLBCL. Forty-four patients with relapsed and 15 patients with primary refractory chemosensitive disease undergoing BEAM (BCNU [carmustine], etoposide, cytarabine, melphalan) conditioning and autologous HSC were included. Immunohistochemical analysis was performed for CD10, BCL-6, MUM1 (allowing classification into GCB and non-GCB-like DLBCL) and BCL-2. Median follow-up of survivors was 25 months; median age at the time of transplantation was 60 years (range 17-77). Thirty-two patients (54%) were classified as having GCB and 27 (46%) as having non-GCB-like DLBCL. Patients with GCB and non-GCB DLBCL did not differ in the risk of progression after HSC transplant (P = 0.78) or overall survival (P = 0.48). In multivariate analysis, only time to progression after initial treatment impacted overall survival. We conclude that patients with relapsed or primary refractory chemosensitive GCB and non-GCB-like DLBCL derive similar benefit from autologous HSC transplant.
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Germinal center B (GCB) and non‐GCB cell‐like diffuse large B cell lymphomas have similar outcomes following autologous haematopoietic stem cell transplantation
British journal of haematology, 2008Co-Authors: Luciano J. Costa, Andrew L. Feldman, Ivana N. Micallef, David J. Inwards, Patrick B. Johnston, Luis F. Porrata, Stephen M. AnsellAbstract:Patients with germinal center B cell-like (GCB) and non-GCB diffuse large B cell lymphomas (DLBCL) receiving first line therapy have distinct prognosis. We explored the differences in outcome following salvage autologous hematopoietic stem cell (HSC) transplantation between patients with GCB and non-GCB DLBCL. Forty-four patients with relapsed and 15 patients with primary refractory chemosensitive disease undergoing BEAM (BCNU [carmustine], etoposide, cytarabine, melphalan) conditioning and autologous HSC were included. Immunohistochemical analysis was performed for CD10, BCL-6, MUM1 (allowing classification into GCB and non-GCB-like DLBCL) and BCL-2. Median follow-up of survivors was 25 months; median age at the time of transplantation was 60 years (range 17-77). Thirty-two patients (54%) were classified as having GCB and 27 (46%) as having non-GCB-like DLBCL. Patients with GCB and non-GCB DLBCL did not differ in the risk of progression after HSC transplant (P = 0.78) or overall survival (P = 0.48). In multivariate analysis, only time to progression after initial treatment impacted overall survival. We conclude that patients with relapsed or primary refractory chemosensitive GCB and non-GCB-like DLBCL derive similar benefit from autologous HSC transplant.
Masahiro Watanabe - One of the best experts on this subject based on the ideXlab platform.
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Electrochemical and Raman Spectroscopic Evaluation of Pt/GCB Durability for the Start/Stop Operating Condition
2012Co-Authors: Masanori Hara, Myoungseok Lee, Yuya Yamashita, Makoto Uchida, Hiroyuki Uchida, Masahiro WatanabeAbstract:In order to reduce the cost of PEFCs, it is required to reduce the amount of Pt used as a catalyst by improving the specific mass activity of Pt-based electrocatalysts for ORR and their durability, especially for the cathode. In particular, corrosion of carbon black (CB) support for commercial Pt/CB (c-Pt/CB) cathode catalysts may be a critical problem for cell durability under certain PEFC operating conditions. To mitigate the corrosion of the carbon support, the use of graphitized carbon blacks (GCB), for which there is a high degree of graphitization, was found to be effective. In this study, durability of Pt nanoparticle catalysts and two types of carbon supports, CB and graphitized carbon black (GCB), for 50 wt% Ptloaded catalysts (c-Pt/CB, commercial Pt/GCB (c-Pt/ GCB), heat treated Pt/GCB (Pt/GCB-HT), and an inhouse-prepared nanocapsule Pt/GCB (n-Pt/GCB)) was evaluated by electrochemical and Raman spectroscopic methods. The Pt-loaded carbon catalysts were tested by means of a standard potential step protocol (0.9 V ↔ 1.3 V vs. RHE, holding 30 s at each potential, 3000 potential cycles for c-Pt/CB and 10000 cycles for c-Pt/GCB, Pt/GCB-HT, and n-Pt/GCB) in MEAs with Nafion as polymer electrolyte membrane at 65 °C with 100% RH H2 (anode) and N2 (cathode). Before the durability test and after given numbers of potential step cycles (N), cyclic voltammetry (CV) was performed to examine changes in electrochemical active surface area (ECA) value of Pt at 65 °C with 100% RH N2 in the cathode and 100% RH H2 in the anode. Confocal micro-Raman spectroscopy (Lab RAM HR-800, HORIBA Jobin Yvon Ltd) was employed to estimate the structural changes of the carbon support. The Raman spectra were obtained by excitation with the radiation from a He–Ne laser (632.8 nm). The durability of the catalysts was investigated in voltage step cycle testing. Figure 1 shows the progress of ECA values normalized to the corresponding initial values for each catalyst. The c-Pt/CB clearly exhibited a much higher reduction in the ECA at the initial stage of cycling, compared to those for the GCB-supported catalysts. The order of the ECA value decreases for the GCB-supported catalysts was c-Pt/GCB > n-Pt/GCB > Pt/ GCB-HT. In addition, the trend of cell performance decrease is consistent with the ECA decrease rate. Slower degradation of ECA and smaller mass activity losses before vs. after durability testing for Pt/GCB compared to CB revealed the higher corrosion resistance of GCB. The results suggested that the essential factors for the maintenance of the ECA values and the cell performance during durability test are the high corrosion resistance of the support material (for GCB), uniform dispersion of the Pt nanoparticles on the support (for n-Pt/GCB), and a slightly increased Pt particle size (for Pt/GCB-HT). Changes in the Raman spectra were clearly detected between the Pt/GCB catalyst before and after durability testing, while only slight differences of spectra were found for c-Pt/CB. The degradation degree of the GCB support was successfully evaluated from changes in band area ratio of the G band to the D1 band, AD1-band/AGband, which was estimated from curve fitting of the spectra. The AD1-band/AG-band ratios for the Pt catalysts before and after durability testing are shown in figure 2. Increases in the AD1-band/AG-band ratio can be clearly seen during the potential cycle testing for the GCB-supported Pt catalysts. The increase of AD1-band/AG-band for the Pt/GCB samples confirm the structural transformation of the surface graphite layer from a highly ordered graphitized carbon phase to a disordered or defected carbon layer due to the oxidation of the surface carbon layer. The order of the degradation level for the GCB-supported catalysts is consistent with the results of the electrochemical analysis, c-Pt/GCB > n-Pt/GCB > Pt/GCB-HT. The degradation rates evaluated by the Raman spectroscopic method were consistent with the results obtained from electrochemical measurements. These results indicate that the degradation of the cell performance is directly related to the oxidative corrosion of GCB supports. Furthermore, the evaluation of AD1-band/AG-band for the Pt/GCB catalysts confirmed that the degradation of the GCB support could be suppressed by heat treatment of the catalysts and uniform dispersion of the Pt nanoparticles on the carbon supports. In our presentation, we will propose models for the catalysts degradation mechanisms during the potential step cycles.
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electrochemical and raman spectroscopic evaluation of pt GCB durability for the start stop operating condition
Meeting Abstracts, 2012Co-Authors: Masanori Hara, Myoungseok Lee, Yuya Yamashita, Makoto Uchida, Hiroyuki Uchida, Masahiro WatanabeAbstract:In order to reduce the cost of PEFCs, it is required to reduce the amount of Pt used as a catalyst by improving the specific mass activity of Pt-based electrocatalysts for ORR and their durability, especially for the cathode. In particular, corrosion of carbon black (CB) support for commercial Pt/CB (c-Pt/CB) cathode catalysts may be a critical problem for cell durability under certain PEFC operating conditions. To mitigate the corrosion of the carbon support, the use of graphitized carbon blacks (GCB), for which there is a high degree of graphitization, was found to be effective. In this study, durability of Pt nanoparticle catalysts and two types of carbon supports, CB and graphitized carbon black (GCB), for 50 wt% Ptloaded catalysts (c-Pt/CB, commercial Pt/GCB (c-Pt/ GCB), heat treated Pt/GCB (Pt/GCB-HT), and an inhouse-prepared nanocapsule Pt/GCB (n-Pt/GCB)) was evaluated by electrochemical and Raman spectroscopic methods. The Pt-loaded carbon catalysts were tested by means of a standard potential step protocol (0.9 V ↔ 1.3 V vs. RHE, holding 30 s at each potential, 3000 potential cycles for c-Pt/CB and 10000 cycles for c-Pt/GCB, Pt/GCB-HT, and n-Pt/GCB) in MEAs with Nafion as polymer electrolyte membrane at 65 °C with 100% RH H2 (anode) and N2 (cathode). Before the durability test and after given numbers of potential step cycles (N), cyclic voltammetry (CV) was performed to examine changes in electrochemical active surface area (ECA) value of Pt at 65 °C with 100% RH N2 in the cathode and 100% RH H2 in the anode. Confocal micro-Raman spectroscopy (Lab RAM HR-800, HORIBA Jobin Yvon Ltd) was employed to estimate the structural changes of the carbon support. The Raman spectra were obtained by excitation with the radiation from a He–Ne laser (632.8 nm). The durability of the catalysts was investigated in voltage step cycle testing. Figure 1 shows the progress of ECA values normalized to the corresponding initial values for each catalyst. The c-Pt/CB clearly exhibited a much higher reduction in the ECA at the initial stage of cycling, compared to those for the GCB-supported catalysts. The order of the ECA value decreases for the GCB-supported catalysts was c-Pt/GCB > n-Pt/GCB > Pt/ GCB-HT. In addition, the trend of cell performance decrease is consistent with the ECA decrease rate. Slower degradation of ECA and smaller mass activity losses before vs. after durability testing for Pt/GCB compared to CB revealed the higher corrosion resistance of GCB. The results suggested that the essential factors for the maintenance of the ECA values and the cell performance during durability test are the high corrosion resistance of the support material (for GCB), uniform dispersion of the Pt nanoparticles on the support (for n-Pt/GCB), and a slightly increased Pt particle size (for Pt/GCB-HT). Changes in the Raman spectra were clearly detected between the Pt/GCB catalyst before and after durability testing, while only slight differences of spectra were found for c-Pt/CB. The degradation degree of the GCB support was successfully evaluated from changes in band area ratio of the G band to the D1 band, AD1-band/AGband, which was estimated from curve fitting of the spectra. The AD1-band/AG-band ratios for the Pt catalysts before and after durability testing are shown in figure 2. Increases in the AD1-band/AG-band ratio can be clearly seen during the potential cycle testing for the GCB-supported Pt catalysts. The increase of AD1-band/AG-band for the Pt/GCB samples confirm the structural transformation of the surface graphite layer from a highly ordered graphitized carbon phase to a disordered or defected carbon layer due to the oxidation of the surface carbon layer. The order of the degradation level for the GCB-supported catalysts is consistent with the results of the electrochemical analysis, c-Pt/GCB > n-Pt/GCB > Pt/GCB-HT. The degradation rates evaluated by the Raman spectroscopic method were consistent with the results obtained from electrochemical measurements. These results indicate that the degradation of the cell performance is directly related to the oxidative corrosion of GCB supports. Furthermore, the evaluation of AD1-band/AG-band for the Pt/GCB catalysts confirmed that the degradation of the GCB support could be suppressed by heat treatment of the catalysts and uniform dispersion of the Pt nanoparticles on the carbon supports. In our presentation, we will propose models for the catalysts degradation mechanisms during the potential step cycles.
