In-situ electrochemical quantification of active sites in Fe-N/C non-precious metal catalysts

The economic viability of low temperature fuel cells as clean energy devices is enhanced by the development of inexpensive oxygen reduction reaction catalysts. Heat treated iron and nitrogen containing carbon based materials (Fe–N/C) have shown potential to replace expensive precious metals. Although significant improvements have recently been made, their activity and durability is still unsatisfactory. The further development and a rational design of these materials has stalled due to the lack of an in situ methodology to easily probe and quantify the active site. Here we demonstrate a protocol that allows the quantification of active centres, which operate under acidic conditions, by means of nitrite adsorption followed by reductive stripping, and show direct correlation to the catalytic activity. The method is demonstrated for two differently prepared materials. This approach may allow researchers to easily assess the active site density and turnover frequency of Fe–N/C catalysts

A catalyst layer optimisation approach using electrochemical impedance spectroscopy for PEM fuel cells operated with pyrolysed transition metal-N-C catalysts

AbstractThe effect of the ionomer to carbon (I/C) ratio on the performance of single cell polymer electrolyte fuel cells is investigated for three different types of non-precious metal cathodic catalysts. Polarisation curves as well as impedance spectra are recorded at different potentials in the presence of argon or oxygen at the cathode and hydrogen at the anode. It is found that a optimised ionomer content is a key factor for improving the performance of the catalyst. Non-optimal ionomer loading can be assessed by two different factors from the impedance spectra. Hence this observation could be used as a diagnostic element to determine the ideal ionomer content and distribution in newly developed catalyst-electrodes. An electrode morphology based on the presence of inhomogeneous resistance distribution within the porous structure is suggested to explain the observed phenomena. The back-pressure and relative humidity effect on this feature is also investigated and supports the above hypothesis. We give a simple flowchart to aid optimisation of electrodes with the minimum number of trials

Time-resolved product observation for CO2 electroreduction using synchronised electrochemistry-mass spectrometry with soft ionisation (sEC-MS-SI).

The mechanistic understanding of electrochemical CO2 reduction reaction (CO2 RR) requires a rapid and accurate characterisation of product distribution to unravel the activity and selectivity, which is yet hampered by the lack of advanced correlative approaches. Here, we present the time-resolved identification of CO2 RR products by using the synchronised electrochemistry-mass spectrometry (sEC-MS). Transients in product formation can be readily captured in relation to electrochemical conditions. Moreover, a soft ionisation (SI) strategy is developed in MS for the direct observation of CO, immune to the interference of CO2 fragments. With the sEC-MS-SI, the kinetic information, such as Tafel slopes and onset potentials, for a myriad of CO2 RR products are revealed and we show the hysteresis seen for the evolution of some species may originate from the potential-driven changes in surface coverage of intermediates. This work provides a real-time picture of the dynamic formation of CO2 RR products

Aqueous redox flow batteries: small organic molecules for the positive electrolyte species

There are a number of critical requirements for electrolytes in aqueous redox flow batteries. This paper reviews organic molecules that have been used as the redox-active electrolyte for the positive cell reaction in aqueous redox flow batteries. These organic compounds are centred around different organic redox active moieties such as the aminoxyl radical (TEMPO and N-hydroxyphthalimide), carbonyl (quinones and biphenols), amine (e.g indigo carmine), ether and thioether (e.g. thianthrene) groups. We consider the key metrics that can be used to assess their performance: redox potential, solubility, redox kinetics, diffusivity, operating pH, stability, and cost. We develop a new figure of merit - the theoretical intrinsic power density - which combines the first four of the aforementioned metrics to allow ranking of different redox couples on just one side of the battery. The organic electrolytes show theoretical intrinsic power densities which are 2-100 times larger than that of the VO2+/VO2+ couple, with TEMPO-derivatives showing the highest performance. Finally, we survey organic positive electrolytes in the literature on the basis of their redox-active moieties and the aforementioned figure of merit

Multifunctional Structural Supercapacitor Composites Based on Carbon Aerogel Modified High Performance Carbon Fiber Fabric

It is well documented that bedrest has adverse outcomes for hospitalized patients. This is especially true for critically ill patients due to life support measures, invasive catheters, and mechanical ventilation. Consequences associated with bedrest in critical care patients include venous thromboembolism, ventilator associated pneumonia, pressure ulcer development, and muscle weakness. Respiratory muscle weakness is associated with prolonged ventilator support and delayed extubation. The Awakening and Breathing Coordination, Delirium Monitoring and Management, and Early Mobility (ABCDE) bundle uses evidence based practice to prevent and treat ICU acquired delirium and weakness. The bundle aims to do this by standardizing care processes in collaboration with the ICU team to promote early mobility in ventilated patients. The purpose of this research study was to determine if the implementation of an early mobility protocol decreased the number of ventilator days for patients who receive mechanical ventilation. A retrospective chart review was conducted at a 16 bed ICU. Group A included 30 subjects (n=30) who were treated pre implementation of the ABCDE bundle and Group B included 39 (n=39) subjects who were treated post implementation of the ABCDE bundle. There were less average ventilator days found in Group A in comparison to Group B. Additionally, there was a significant difference found in the ICU length of stay pre implementation (M=9.4, SD=4.4) and post implementation (M=5.7, SD=2.6) of the ABCDE bundle for early mobility, t (65) =4.3, p = 0.00005. The APRN can use the evidence in the ABCDE bundle to guide care to critically ill patients that are mechanically ventilated. Utilizing the ABCDE bundle additionally allows the APRN to be instrumental in improving patient outcomes through interdisciplinary collaboration

Oxygen reduction reaction activity in non-precious single-atom (M–N/C ) catalysts-contribution of metal and carbon/nitrogen framework-based sites.

We examine the performance of a number of single-atom M-N/C electrocatalysts with a common structure in order to deconvolute the activity of the framework N/C support from the metal M-N4 sites in M-N/Cs. The formation of the N/C framework with coordinating nitrogen sites is performed using zinc as a templating agent. After the formation of the electrically conducting carbon-nitrogen metal-coordinating network, we (trans)metalate with different metals producing a range of different catalysts (Fe-N/C, Co-N/C, Ni-N/C, Sn-N/C, Sb-N/C, and Bi-N/C) without the formation of any metal particles. In these materials, the structure of the carbon/nitrogen framework remains unchanged-only the coordinated metal is substituted. We assess the performance of the subsequent catalysts in acid, near-neutral, and alkaline environments toward the oxygen reduction reaction (ORR) and ascribe and quantify the performance to a combination of metal site activity and activity of the carbon/nitrogen framework. The ORR activity of the carbon/nitrogen framework is about 1000-fold higher in alkaline than it is in acid, suggesting a change in mechanism. At 0.80 VRHE, only Fe and Co contribute ORR activity significantly beyond that provided by the carbon/nitrogen framework at all pH values studied. In acid and near-neutral pH values (pH 0.3 and 5.2, respectively), Fe shows a 30-fold improvement and Co shows a 5-fold improvement, whereas in alkaline pH (pH 13), both Fe and Co show a 7-fold improvement beyond the baseline framework activity. The site density of the single metal atom sites is estimated using the nitrite adsorption and stripping method. This method allows us to deconvolute the framework sites and metal-based active sites. The framework site density of catalysts is estimated as 7.8 × 1018 sites g-1. The metal M-N4 site densities in Fe-N/C and Co-N/C are 9.4 × 1018 sites-1 and 4.8 × 1018 sites g-1, respectively

The Flexi Planar Fuel Cell

The Flexi Planar fuel cell is a new type of lightweight polymer electrolyte fuel cell design. The approach utilises standard, reliable and low cost printed circuit board fabrication processes. An iterative approach is adopted and feasibility along with excellent test characteristics for short modules have been successfully demonstrated

Highly selective O2 reduction to H2O2 catalyzed by cobalt nanoparticles supported on nitrogen-doped carbon in alkaline solution

We report the synthesis of cobalt nanoparticles supported on nitrogen-doped carbon (CoNPs@N/C), which can reduce O2 into H2O2 with high selectivity (up to 93%) in 0.1 M KOH electrolyte and retains >90% activity even after 10 h polarization. The catalyst achieves a current density of 1 mA cm–2 at 0.76 V(RHE) and a peroxide production rate of ∼3.8molH2O2 gCo–1 h–1 over a 10 h period. Our study also highlights the requirement for good peroxide production catalysts to be poor hydrogen peroxide disproportionation catalysts. We show how the high activity of the CoNPs@N/C catalyst is correlated with low activity toward the peroxide disproportionation reaction

Structural power performance requirements for future aircraft integration

This paper investigates the use of structural power composites in Airbus A220-100 aircraft cabins by integrating floor panels with face sheets made of structural power composites to power the in-flight entertainment system. This application requires a minimum specific energy of 305 Wh/kg and a minimum specific power of 0.610 kW/kg. The static and dynamic loads for which the floor panels must be certified require an in-plane Young’s modulus of 50 GPa, a compressive strength of 225 MPa and a tensile strength of 119 MPa. Structural power composite floor panels are predicted to yield mass savings of 324 kg, annual cost savings of £85,000 per aircraft and annual reductions in CO2 and NOx emissions of 343 tonnes and 1.4 tonnes respectively. However, addressing challenges such as fire-resistance, long term cycling performance and public perception of structural power composites are necessary to enable widespread use of such materials on-board airliners