Tara Dahn

Impact of Loading in RRDE Experiments on Fe–N–C Catalysts: Two- or Four-Electron Oxygen Reduction?

We have investigated the impact of electrocatalyst loading on rotating ring-disk electrode (RRDE) experiments for the oxygen reduction reaction on Fe-N-C catalysts (ORR) in acid medium. In particular, the fraction of H 2 O 2 produced as a function of catalyst loading was studied. A dramatic increase in H 2 O 2 release was observed as the catalyst loading was decreased. For the same non-noble metal catalyst (NNMC), the fraction of produced H 2 O 2 varied between less than 5% and greater than 95%, depending on the catalyst loading. These observations suggest that oxygen reduction occurs stepwise, via H 2 O 2 , and if the catalyst is sparsely loaded, the produced H 2 O 2 cannot be efficiently reduced to H 2 O before it escapes. These studies have important implications for fundamental studies of ORR on NNMCs.

Oxygen Reduction Behavior of Highly Porous Non-Noble Metal Catalysts Prepared by a Template-Assisted Synthesis Route

Highly porous non-noble metal catalysts have been prepared by template-assisted synthesis, a nanocasting procedure. A mesoporous silica gel was used to prepare different oxygen reduction catalysts. The synthesis procedure consists of the following steps: impregnation of the template with different transition metal salts (FeCl 3 or CoCl 2 ), pore filling of the impregnated host material with pyrrole, polymerization of pyrrole with hydrochloric acid and subsequent carbonization in argon as well as final liberation of the catalyst material by dissolving the template framework and the transition metal in hydrofluoric acid. The obtained catalyst samples are highly porous and exhibit outstanding oxygen reduction behavior. The Brunauer, Emmett, and Teller method surface areas between 670 and 1030 m 2 /g and pore volumes ranging from 1.6 to 2.4 cm 3 /g have been observed. Onset potentials up to 0.85 V were recorded during the oxygen reduction reaction (ORR). Different parameters affecting ORR activity (e.g., metal source, metal concentration of host material, annealing temperature) have been investigated and are discussed. Corresponding non-noble metal catalysts have been characterized by X-ray diffraction measurements, elemental analysis, scanning electron microscopy, and nitrogen adsorption.

The effect of heating temperature and nitric acid treatments on the performance of Cu- and Zn-based broad spectrum respirator carbons.

Impregnated activated carbons (IACs) that are used in broad spectrum gas mask applications have historically contained copper and/or zinc impregnants. The addition of an oxidizing agent, such as nitric acid (HNO(3)) can be useful in distributing the metallic impregnants uniformly on the activated carbon substrate. In this work, we study IACs prepared from copper nitrate (Cu(NO(3))(2)) and zinc nitrate (Zn(NO(3))(2)) precursors as a function of HNO(3) content present in the impregnating solution and as a function of heating temperature. The gas adsorption capacity of the IACs was determined by dynamic flow testing using sulfur dioxide (SO(2)), ammonia (NH(3)), hydrogen cyanide (HCN) and cyclohexane (C(6)H(12)) challenge gases under dry and humid conditions. The thermal decomposition and distribution of the impregnant on the activated carbon substrate is studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis techniques. Relationships between gas adsorption capacity, impregnant distribution and the species of surface impregnants are discussed.

Fe–C–N Oxygen-Reduction Catalysts Prepared by Mechanochemical Reaction

Fe-C-N oxygen-reduction catalysts were prepared by mechanochemical reaction of Fe x N (x = 2-4) and graphite under Ar using high-energy ballmilling. The activity of the catalyst toward the oxygen reduction reaction (ORR) depends on the ballmilling time and on the Fe x N precursor content. Heat-treatment up to 600°C does not significantly affect the activity, but the activity strongly decreases as the samples are heat-treated above 800°C in argon. The onset potential of a typical sample ballmilled for 12 h is 0.72 V versus reversible hydrogen electrode. About 20% of the product of oxygen reduction is H 2 O 2 and the other 80% is water. The X-ray diffraction pattern of the ballmilled material shows the formation of Fe 7 C 3 and disordered carbon, which presumably contains nitrogen, because the ball mills are sealed and the nitrogen cannot escape. This work demonstrates that mechanochemical synthesis is a useful technique for the preparation of Fe-C-N ORR catalysts.

The effect of co-impregnated acids on the performance of Zn-based broad spectrum respirator carbons

Impregnated activated carbons (IACs) that are used in multi-gas respirator applications usually contain copper and/or zinc impregnants. Co-impregnating with properly selected acids can improve the distribution of the metallic impregnant on the carbon and improve the gas adsorption capacity of the IAC. In this work a comparative study of some common acids co-impregnated with a zinc nitrate (Zn(NO(3))(2)) precursor is performed. The IACs were heated in an inert atmosphere at temperatures which promoted the thermal decomposition of Zn(NO(3))(2) to zinc oxide (ZnO). The gas adsorption properties of the IACs were tested using ammonia (NH(3)), sulphur dioxide (SO(2)) and hydrogen cyanide (HCN) challenge gases. Powder X-ray diffraction (XRD) was used to identify the impregnant species present after heating and to study impregnant distribution. Gravimetric analysis was used to determine the impregnant loading, and help to identify the impregnant species after heating. The interactions between the co-impregnated acid and Zn(NO(3))(2) precursor during heating are discussed. The relationship between impregnant species and gas adsorption capacity is discussed.

Does Point-of-Care Ultrasonography Improve Clinical Outcomes in Emergency Department Patients With Undifferentiated Hypotension? An International Randomized Controlled Trial From the SHoC-ED Investigators

Study objective Point‐of‐care ultrasonography protocols are commonly used in the initial management of patients with undifferentiated hypotension in the emergency department (ED). There is little published evidence for any mortality benefit. We compare the effect of a point‐of‐care ultrasonography protocol versus standard care without point‐of‐care ultrasonography for survival and clinical outcomes. Methods This international, multicenter, randomized controlled trial recruited from 6 centers in North America and South Africa and included selected hypotensive patients (systolic blood pressure <100 mm Hg or shock index >1) randomized to early point‐of‐care ultrasonography plus standard care versus standard care without point‐of‐care ultrasonography. Diagnoses were recorded at 0 and 60 minutes. The primary outcome measure was survival to 30 days or hospital discharge. Secondary outcome measures included initial treatment and investigations, admissions, and length of stay. Results Follow‐up was completed for 270 of 273 patients. The most common diagnosis in more than half the patients was occult sepsis. We found no important differences between groups for the primary outcome of survival (point‐of‐care ultrasonography group 104 of 136 patients versus standard care 102 of 134 patients; difference 0.35%; 95% binomial confidence interval [CI] –10.2% to 11.0%), survival in North America (point‐of‐care ultrasonography group 76 of 89 patients versus standard care 72 of 88 patients; difference 3.6%; CI –8.1% to 15.3%), and survival in South Africa (point‐of‐care ultrasonography group 28 of 47 patients versus standard care 30 of 46 patients; difference 5.6%; CI –15.2% to 26.0%). There were no important differences in rates of computed tomography (CT) scanning, inotrope or intravenous fluid use, and ICU or total length of stay. Conclusion To our knowledge, this is the first randomized controlled trial to compare point‐of‐care ultrasonography to standard care without point‐of‐care ultrasonography in undifferentiated hypotensive ED patients. We did not find any benefits for survival, length of stay, rates of CT scanning, inotrope use, or fluid administration. The addition of a point‐of‐care ultrasonography protocol to standard care may not translate into a survival benefit in this group.