The role of electronic properties of Pt and Pt alloys for enhanced reformate electro-oxidation in polymer electrolyte membrane fuel cells

One major challenge of PEM fuel cells development is to overcome the activity and durability issues of the current anode materials which are susceptible to hydrogen impurities. To design stable and efficient catalysts with enhanced reformate tolerance, a comprehensive understanding of the underlying mechanisms is crucial. In this work, the CO and CO2 tolerance of a series of Pt-based catalysts are tested in a PEM fuel cell. We report that the CO tolerance is the highest for PtMo/C followed by PtCoMo/C, PtRuMo/C, PtRuPb/C, PtRu/C, PtCo/C, PtFe/C, PtNi/C and Pt/C; while the CO2 tolerance increases in the order: PtCo, PtNi> PtRuPb> PtRu> PtCoMo> PtRuMo> PtFe> Pt> PtMo. In situ XAS measurements in combination with FEFF8 calculations are performed to correlate the CO and CO2 tolerance trends with the electronic properties of these Pt-based alloy catalysts. We find that the anode overpotential in the presence of CO2 can be generally related to the experimental Pt d-band vacancy or calculated d-band center, and thus governed by the Pt electronic properties modified by the alloyed metal(s). No such correlation is observed between the anode overpotential in the presence of CO and Pt electronic properties, which highlights the key roles of Mo or Ru in improving CO tolerance via promotion and bifunctional mechanisms. Building upon these results a new ternary alloy PtCoMo/C was synthesized. This electrocatalyst shows the best reformate tolerance in low temperature PEM fuel cells by taking advantage of the bifunctional mechanism induced by Mo and the ligand effect induced by Co simultaneously. Our findings put forward a theory which gives a strong perspective for further research and development of new inexpensive catalysts with superior CO tolerance and durability

Activity Descriptor Identification for Oxygen Reduction on Nonprecious Electrocatalysts: Linking Surface Science to Coordination Chemistry

Developing nonprecious group metal based electrocatalysts for oxygen reduction is crucial for the commercial success of environmentally friendly energy conversion devices such as fuel cells and metal–air batteries. Despite recent progress, elegant bottom-up synthesis of nonprecious electrocatalysts (typically Fe–N_<i>x</i>/C) is unavailable due to lack of fundamental understanding of molecular governing factors. Here, we elucidate the mechanistic origin of oxygen reduction on pyrolyzed nonprecious catalysts and identify an activity descriptor based on principles of surface science and coordination chemistry. A linear relationship, depicting the ascending portion of a volcano curve, is established between oxygen-reduction turnover number and the Lewis basicity of graphitic carbon support (accessed via C 1s photoemission spectroscopy). Tuning electron donating/withdrawing capability of the carbon basal plane, conferred upon it by the delocalized π-electrons, (i) causes a downshift of e_g-orbitals (d_<i>z</i>²) thereby anodically shifting the metal ion’s redox potential and (ii) optimizes the bond strength between the metal ion and adsorbed reaction intermediates thereby maximizing oxygen-reduction activity

Design method of PID-type model predictive iterative learning control based on the two-dimensional generalized predictive control scheme

Conference Name:2012 12th International Conference on Control, Automation, Robotics and Vision, ICARCV 2012. Conference Address: Guangzhou, China. Time:December 5, 2012 - December 7, 2012.For the repetitive, cyclic or batch processes, iterative learning control is essentially a two-dimensional feedback control. By transforming the iterative learning control into a two-dimensional generalized predictive control, a new model predictive iterative leaning control scheme is proposed in this paper for the repetitive, cyclic or batch processes with both time-wise and cycle-wise dynamics. As the proportional, integral and derivative of the prediction errors are considered in the cost function, the proposed ILC scheme can be referred to as a PID-type model predictive iterative learning control (PID-MPILC). Compared with the two-dimensional model predictive iterative learning control (2D-MPILC) proposed in the previous works, the proposed PID-MPILC can provide much better control performances not only along cycle but also along time, which is illustrated by the numerical simulation. 漏 2012 IEEE

Unveiling the Degradation Nature of Pt/NbOx/C Catalysts for Oxygen Reduction Reaction via in situ X-ray Absorption Spectroscopy

Among various metal nanoparticles supported on metal oxide (MMO) catalysts, the Pt/NbOx/C system has promising oxygen reduction reaction (ORR) activity as cathode for proton exchange membrane fuel cells (PEMFCs). Herein, we study a series of Pt/NbOx/C catalysts with tunable structural and electronic properties via physical vapor deposition and unravel the nature of metal and metal oxide interaction (MMOI) by characterizing this system under reactive conditions. By conducting in situ X-ray absorption spectroscopy (XAS) experiments, we demonstrate the Pt preferably interacts with O but not Nb in the Pt/NbOx/C system and such Pt-O interaction benefits the ORR activity via electronic effect rather than strain effect. We also provide clear evidence for the formation of metallic Nb phase at the early stage of PEMFC operation and identify severe particle growth of Pt after long-term PEMFC operation. These findings deepen our understanding of the degradation mechanism of MMO catalysts during long-term PEMFC operation

The Challenge of Achieving a High Density of Fe-Based Active Sites in a Highly Graphitic Carbon Matrix

As one of the most promising platinum group metal-free (PGM-free) catalysts for oxygen reduction reaction (ORR), Fe&#8315;N&#8315;C catalysts with a high density of FeNx moieties integrated in a highly graphitic carbon matrix with a proper porous structure have attracted extensive attention to combine the high activity, high stability and high accessibility of active sites. Herein, we investigated a ZnCl2/NaCl eutectic salts-assisted ionothermal carbonization method (ICM) to synthesize Fe&#8315;N&#8315;C catalysts with tailored porous structure, high specific surface area and a high degree of graphitization. However, it was found to be challenging to anchor a high density of FeNx sites onto highly graphitized carbon. Iron precursors with preexisting Fe&#8315;N coordination were required to form FeNx sites in the nitrogen-doped carbon with a high degree of graphitization, while individual Fe and N precursors led to a Fe&#8315;N&#8315;C catalyst with poor-ORR activity. This provides valuable insights into the synthesis-structure relationship. Moreover, the FeNx moieties were identified as the major active sites in acidic conditions, while both FeNx sites and Fe2O3 were found to be active in alkaline medium

The genus Catathelasma (Catathelasmataceae, Basidiomycota) in China

Two new species, Catathelasma laorentou and C. subalpinum, are described on the basis of morphological characters, phylogenetic evidence, host preferences and geographic distributions. A taxonomic key to the known species in China is also provided to facilitate identification. Based on samples from temperate Asia, Europe and North America, the phylogeny of Catathelasma was reconstructed using the internal transcribed spacer (ITS) region, the large subunit (LSU) of the ribosomal DNA and the translation elongation factor 1-alpha (TEF1). The phylogenetic results showed that Catathelasma contains two monophyletic clades: the /subalpinum clade and the /imperiale clade. The Asian species C. laorentou and C. subalpinum are closely related to the North American C. sp. (labelled as C. ventricosum in GenBank) in the /subalpinum clade, whereas C. imperiale and C. singeri are closely related in the /imperiale clade

The genus Catathelasma (Catathelasmataceae, Basidiomycota) in China

Two new species, Catathelasma laorentou and C. subalpinum, are described on the basis of morphological characters, phylogenetic evidence, host preferences and geographic distributions. A taxonomic key to the known species in China is also provided to facilitate identification. Based on samples from temperate Asia, Europe and North America, the phylogeny of Catathelasma was reconstructed using the internal transcribed spacer (ITS) region, the large subunit (LSU) of the ribosomal DNA and the translation elongation factor 1-α (TEF1).The phylogenetic results showed that Catathelasma contains two monophyletic clades: the /subalpinum clade and the /imperiale clade. The Asian species C. laorentou and C. subalpinum are closely related to the North American C. sp. (labelled as C. ventricosum in GenBank) in the /subalpinum clade, whereas C. imperiale and C. singeri are closely related in the /imperiale clade