Gram-scale synthesis of alkoxide-derived nitrogen-doped carbon foam as a support for Fe-N-C electrocatalysts

Non-platinum group metal (non-PGM) catalysts for the oxygen reduction reaction (ORR) are set to reduce the cost of polymer electrolyte membrane fuel cells (PEFCs), by replacing platinum at the cathode. We previously developed unique nitrogen-doped carbon foams by template-free pyrolysis of alkoxide powders synthesized using a high temperature and high pressure solvothermal reaction. These were shown to be effective ORR electrocatalysts in alkaline media. Here, we present a new optimised synthesis protocol which is carried out at ambient temperature and pressure, enabling us to safely increase the batch size to 2 g, increase the yield by 60%, increase the specific surface area to 1866 m2/g, and control the nitrogen content (between 1.0 and 5.2 at%). These optimized nitrogen-doped carbon foams are then utilized as effective supports for Fe-N-C catalysts for the ORR in acid media, whilst multiphysics modelling is used to gain insight into the electrochemical performance. This work highlights the importance of the properties of the carbon support in the design of Pt-free electrocatalysts

New methods for Prediction of Geomechanical Failure-time

KRMS 2008: Korean Rock Mechanics Symposium on International Cooperation and Rock Engineering for Development of Mineral Resources and Infrastructures. 22-23 October 2008. Chonnam National University, Gwangju, Korea

A new practical method for prediction of geomechanical failure-time

Predicting the failure-time of geo-hazards is an important rock mechanics problem. We first evaluated the validity of the INVerse-velocity (INV) method to predict failure-time of rock mass and landslides. This method utilizes rates of displacement or strain to predict the actual failure-time (Tf), so the value of total displacement or strain before “failure” is not crucial. Second, we developed a new method for computing failure-time predictions based on the SLOpe (gradient) to predict Tf, termed the SLO method. Finally, a simple conceptualised model representing “safe” and “unsafe” predictions was proposed. To validate these hypotheses, prediction of rock mass failure in the Asamushi and Vaiont landslides (in situ studies) was conducted. Furthermore, laboratory conditions were incorporated into the research, which include predictions using circumferential strain and axial strain from uniaxial compression creep test on Shikotsu welded tuff (SWT), and predictions of failure-time for Inada granite under Brazilian creep tests. It was found that the SLO method is better than the INV method; SLO gave safe predictions in all the cases. In contrast, INV tends to give unsafe predictions (predicted failure-time Tfp>Tf). Our findings reveal that predictions using circumferential strain are better than those made using axial strain for SWT, and notably, given failure with very short tertiary creep, the methods tend to show limited reliability. However, the SLO method could find extensive application in predicting failure-time of geo-hazards, for instance, roof wall failure in mines, etc

Durability of template-free Fe-N-C foams for electrochemical oxygen reduction in alkaline solution

Due to the high cost and limited availability of platinum, the development of non-platinum-group metals (non-PGM) catalysts is of paramount importance. A promising alternative to Pt are Fe-N-C-based materials. Here we present the synthesis, characterization and electrochemistry of a template-free nitrogen-doped carbon foam, impregnated with iron. This low-cost and gram-scale method results in materials with micron-scale pore size and large surface area (1600 m2g-1). When applied as an oxygen reduction reaction (ORR) electrocatalyst in alkaline solution, the Fe-N-C foams display extremely high initial activity, slightly out-performing commercially available non-PGM catalysts (NCP-2000, Pajarito Powder). The load-cycle durability in alkaline solution is investigated, and the performance steadily degrades over 60,000 potential cycles, whilst the commercial catalyst is remarkably stable. The post-operation catalyst microstructure is elucidated by transmission electron microscopy (TEM), to provide insight into the degradation processes. The resulting images suggest that potential cycling leads to leaching of atomically dispersed Fe-N2/4 sites in all the catalysts, whereas encapsulated iron nanoparticles are protected

Superhydrophobic fluorinated carbon powders for improved water management in hydrogen fuel cells

Under high current density operation, the efficiency of polymer electrolyte fuel cells (PEFCs) can dramatically decrease. This is due to water accumulation at the cathode side, preventing oxygen diffusion to the electrocatalyst. As such, effective water management is of vital importance by use of a suitable gas diffusion layer (GDL) and/or microporous layer (MPL). MPLs generally consist of carbon black as the porous electron conducting phase, and polytetrafluoroethylene (PTFE) as a hydrophobic binder. Here, we instead use superhydrophobic fluorinated carbon powder in the MPL as a novel material to decrease the required PTFE content. It is confirmed that the water contact angle of the MPL can be increased from 131° to 151° by using fluorinated carbon. Moreover, the fluorinated carbon MPL shows lower oxygen transport resistance at high humidity. Furthermore, in single fuel cell tests at various temperatures and relative humidity values, the I–V performance is significantly and consistently better than for the conventional MPL. These results confirm that fluorinated carbon is a promising new material for water management in the MPLs of PEFCs