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The effect of nitrogen (N) and iron (Fe) on oxygen reduction reaction (ORR) was investigated by using carbon nanowalls (CNWs) as carbon matrix. The dopings of N and Fe into CNWs are carried out by N plasma and Fe sputtering, respectively. The onset potentials corresponding to ORR activities are evaluated from steady-state curve of cyclic voltammogram. The composition and structure of CNW catalysts before and after ORR measurements are characterized by X-ray photoelectron spectroscopy (XPS). The onset potential increases in the order of non-, N- and Fe-N-doped CNW catalysts. The ORR activity for N-doped CNW catalysts is ascribed to pyridinic N stabilized near the surface of carbon matrix. The higher ORR activity for Fe-N-doped CNW catalysts is attributed to trace Fe-N rather than pyridinic N near the surface. Additionally, it is shown that such ORR activities due to pyridinic N and Fe-N near the surface are further promoted by Fe and Fe-N incorporated beneath the surface. These knowledges provide effective strategy for the synthesis of Fe-N-doped carbon catalysts with higher ORR activities.

In this work, a platinum group metal-free (PGM-free) catalyst based on iron as transitional metal and Nicarbazin (NCB) as low cost organic precursor was synthesized using Sacrificial Support Method (SSM). The catalyst was then incorporated into a large area air-breathing cathode fabricated by pressing with a large diameter pellet die. The electrochemical tests in abiotic conditions revealed that after a couple of weeks of successful operation, the electrode experienced drop in performances in reason of electrolyte leakage, which was not an issue with the smaller electrodes. A decrease in the hydrophobic properties over time and a consequent cathode flooding was suspected to be the cause. On the other side, in the present work, for the first time, it was demonstrated the proof of principle and provided initial guidance for manufacturing MFC electrodes with large geometric areas. The tests in MFCs showed a maximum power density of 1.85 W m−2. The MFCs performances due to the addition of Fe-NCB were much higher compared to the iron-free material. A numerical model using Nernst-Monod and Butler-Volmer equations were used to predict the effect of electrolyte solution conductivity and distance anode-cathode on the overall MFC power output. Considering the existing conditions, the higher overall power predicted was 3.6 mW at 22.2 S m−1 and at inter-electrode distance of 1 cm., Graphical abstract Iron-Nicarbazin derived platinum group metal-free electrocatalyst was incorporated into a scalable-size air-breathing cathodes and tested in microbial fuel cells. Maximum power density of 1.85 W m−2 was achieved initially and then decreased to 1.25 W m−2 after 22 days operations.Image 1, Highlights • Fe-based material was used as catalyst for ORR in MFCs. • The catalyst was incorporated into a scalable-size air breathing cathode. • MFC had an initial power density of 1.85 W m−2. • The effect of solution conductivity and electrodes distance is evaluated on MFC performance. • Higher power predicted was 3.6 mW at 22.2 S m−1 and at electrode distance of 1 cm.

In the search for active cathode catalysts for polymer electrolyte fuel cells (PEFCs) using inexpensive materials several valve metal oxide electrodes TiO(x) ZrO(x), and TaO(x) with corresponding binary oxide electrodes were selected for the evaluation of catalytic activity for oxygen reduction reaction (ORR) by means of cyclic voltammetry in 0 1 M HClO(4) at 60 C These oxide electrodes were prepared mainly by the dip-coating method on a titanium plate substrate at a temperature between 400 degrees C and 500 degrees C and were characterized by scanning electron microscopy (SEM) X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS) Among the oxide-coated electrodes investigated Ti(0) (7)Zr(0) (3)O(x)/Ti provided the highest ORR specific activity with an onset potential E(ORR) of 0 86V vs RHE during the cathodic potential sweep Fine TaO(x) particles prepared as an extension of the dip-coating method showed very high catalytic activity determined by means of hydrodynamic voltammetry in 0 1 M HClO(4) at 30 degrees C with an E(ORR) of 0 90 V vs RHE, Article, ELECTROCHIMICA ACTA

Tantalum (Ta)-added tungsten carbide (WC) (WC+Ta) was examined in order to obtain surperior characteristics instability and electrocatalytic activity for the oxygen reduction reaction (ORR) in acid electrolyte. The stability and the electrocatalytic activity of the WC+Ta catalyst were electrochemically investigated and compared to the pure WC. It was proved that the stability of the tungsten carbide was significantly increased by the addition of tantalum compared to the pure WC. The enhanced stability might be due to the formation of the W-Ta alloy in the WC + Ta catalyst. The reduction current of the WC + Ta catalyst for the ORR was observed at a potential of 0.8 V (versus dynamin hydrogen eletrode (DHE)) or less noble potential. This value was about 0.35 V higher than that of the pure WC. The enhanced electrocatalytic activity for the ORR might be caused by the presence of tungsten carbide, which exists on the surface and/or sub-surface. (C) 2004 Elsevier Ltd. All rights reserved.

Due to their availability and electrochemical versatility, carbon-based electrodes are becoming an increasingly popular option as electrocatalysts for fuel cells and metal-air batteries. Additionally, they show great potential as bifunctional catalysts for the oxygen reduction and evolution reactions (ORR/OER) in an alkaline medium. However, to compete with state-of-the-art catalysts, the nature of the active sites and the surface stability under reaction conditions need to be understood in depth. Here, we present a principle study on highly oriented pyrolytic graphite (HOPG), evaluating the surface behavior under both ORR and OER conditions in 0.1MKOH. We use noise analysis in electrochemical scanning tunneling microscopy (n-EC-STM) to monitor and compare ORR and OER active sites with resolution down to the nanoscale. Furthermore, surface degradation can be evaluated during the operation. We find that close to the respective reaction onset, step sites and defects are active for both ORR and OER. Terraces sites are largely inactive and only become involved in the OER at higher potentials. This could imply corrosion of the carbon. However, since the observed surface structures remain unaltered before and after applying the OER in our experiments, we find no clear evidence of surface destruction. These fundamental insights could inspire further research concerning the active sites and stability of carbon-based catalysts as well as carbon support structures, to discover ways to tune the surface activity and stability to the dedicated purpose.