Due to the Fenton reaction, the presence of Fe and peroxide in electrodes generates free radicals causing serious degradation of the organic ionomer and the membrane. Pt-free and Fe-free cathode catalysts therefore are urgently needed for durable and inexpensive proton exchange membrane fuel cells (PEMFCs). Herein, a high-performance nitrogen-coordinated single Co atom catalyst is derived from Co-doped metal-organic frameworks (MOFs) through a one-step thermal activation. Aberration-corrected electron microscopy combined with X-ray absorption spectroscopy virtually verifies the CoN coordination at an atomic level in the catalysts. Through investigating effects of Co doping contents and thermal activation temperature, an atomically Co site dispersed catalyst with optimal chemical and structural properties has achieved respectable activity and stability for the oxygen reduction reaction (ORR) in challenging acidic media (e.g., half-wave potential of 0.80 V vs reversible hydrogen electrode (RHE). The performance is comparable to Fe-based catalysts and 60 mV lower than Pt/C -60 μg Pt cm ). Fuel cell tests confirm that catalyst activity and stability can translate to high-performance cathodes in PEMFCs. The remarkably enhanced ORR performance is attributed to the presence of well-dispersed CoN active sites embedded in 3D porous MOF-derived carbon particles, omitting any inactive Co aggregates.

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Highly ordered Pt alloy structures are proven effective to improve their catalytic activity and stability for the oxygen reduction reaction (ORR) for proton exchange membrane fuel cells. Here, we report a new approach to preparing ordered PtCo intermetallic nanoparticles through a facile thermal treatment of Pt nanoparticles supported on Co-doped metal-organic-framework (MOF)-derived carbon. In particular, the atomically dispersed Co sites, which are originally embedded into MOF-derived carbon, diffuse into Pt nanocrystals and form ordered PtCo structures. It is very crucial for the formation of the ordered PtCo to carefully control the doping content of Co into the MOFs and the heating temperatures for Co diffusion. The optimal PtCo nanoparticle catalyst has achieved significantly enhanced activity and stability, exhibiting a half-wave potential up to 0.92 V vs reversible hydrogen electrode (RHE) and only losing 12 mV after 30 000 potential cycling between 0.6 and 1.0 V. The highly ordered intermetallic structure was retained after the accelerated stress tests made evident by atomic-scale elemental mapping. Fuel cell tests further verified the high intrinsic activity of the ordered PtCo catalysts. Unlike the direct use of MOF-derived carbon supports for depositing Pt, we utilized MOF-derived carbon containing atomically dispersed Co sites as Co sources to prepare ordered PtCo intermetallic catalysts. The new synthesis approach provides an effective strategy to develop active and stable Pt alloy catalysts by leveraging the unique properties of MOFs such as 3D structures, high surface areas, and controlled nitrogen and transition metal dopings.

1 The possible role of sarcoplasmic reticulum (SR) Ca 2+ stores in hypoxic pulmonary vasoconstriction (HPV) is not well understood. In order to assess the possible role of intracellular Ca 2+ release from SR Ca 2+ stores in HPV, we examined the e ects of: (1) ryanodine (10 mM) depletion of intracellular Ca 2+ stores, and (2) thapsigargin (THAPS, 2 mM) or cyclopiazonic acid (CPA, 10 mM) depletion of intracellular Ca 2+ stores on HPV in canine pulmonary artery. 2 Isometric tension was measured from arterial ring suspended in Krebs-Henseliet solution (K-H) bubbled with 95%O 2 /5%CO 2 . Hypoxia was induced by bubbling phenylephrine (PE, 1 mM) precontracted rings with 95%N 2 /5%CO 2 . HPV was observed in both intact and endothelial-denuded arteries and expressed as % of maximal KCl contraction (%T kmax )=21.3+3.2%; n=13 and 21.7+4%; n=4, respectively. 3 When SR ca eine sensitive Ca 2+ stores were depleted by pretreatment with ryanodine and brief ca eine (15 mM) exposure, the hypoxic response was signifcantly reduced to 19.1+9.2% of the control hypoxic contraction (n=7; P50.001) with little or no e ect on PE or KCl contractions. On the other hand, in normoxic rings pretreated with THAPS or CPA, the PE responses were signi®cantly reduced (%T kmax =18.2+3.1% compared to 39.0+3.9% in control; n=16; P50.001; %T kmax =3.4+1.6% compared to 49.9+7.9% in control; n=6; P50.001; respectively) with no signi®cant e ect on ca eineinduced contractions, suggesting that both THAPS and CPA preferentially deplete InsP 3 -sensitive Ca 2+ stores, without a ecting the ca eine-sensitive Ca 2+ store; consistent with the existence of separate and independent InsP 3 and ca eine-sensitive Ca 2+ stores in this preparation. 4 When hypoxia was induced in the presence of THAPS or CPA, developed tension was signi®cantly larger than control (%T kmax =64.5+6.0%; n=16; P50.05%; %T kmax =78.2+15%; n=6; P50.05; respectively), was partially blocked by nisoldipine (10 mM) and ryanodine (%T kmax =20.3+3.7%; n=6), and nearly completely blocked by SK&F 96365 (50 mM). However, the actions of SK&F 96365 appeared to be nonselective since this compound also signi®cantly reduced contractions elicited by KCl, PE and ca eine. 5 Finally, evidence was obtained suggesting: (a) that at least some of the Ca 2+ released from the ca eine-and ryanodine-sensitive Ca 2+ stores by hypoxia may be taken up and bu ered by the InsP 3 -sensitive Ca 2+ stores, and (b) the apparent dependence of HPV on extracellular Ca 2+ entry pathways may be partially due to the dependence of the Ca 2+ content of intracellular SR Ca 2+ stores on sarcolemmal Ca 2+ entry pathways. 6 These data suggest that ca eine-and ryanodine-sensitive SR Ca 2+ stores contribute signi®cantly to HPV under normal conditions and, in the presence of THAPS or CPA, an additional nisoldipine-and ryanodine-insensitive Ca 2+ entry pathway is evoked by hypoxia.