Raghuram Chetty

Palladium (Pd) dendrites on carbon black support were synthesized by a simple template/surfactant-free electrochemical deposition. In comparison to Pd spherical deposit obtained on non-activated carbon, Pd deposited on an electrochemically activated carbon displayed a dendritic morphology with increased electrochemical surface area and showed enhanced catalytic activity for formic acid oxidation. The effect of electrochemical activation and deposition cycles were studied in relation to the growth and morphological features of Pd deposit. Scanning electron micrographs and X-ray diffraction studies showed a transition in Pd morphology from spheres to dendrites when the carbon support was subjected to varying cycles of electrochemical activation, prior to Pd deposition. Raman and X-ray photoelectron spectra results showed that the defects induced during electrochemical activation on carbon played a major role in tailoring the Pd morphology.

Palladium (Pd) dendrites were synthesized on electrochemically activated carbon (Vulcan XC-72R) support by a simple template free potentiostatic (constant voltage) deposition. Scanning electron micrographs displayed a dendritic morphology when deposited at potentials <0.5 V (vs. RHE), whereas spherical aggregates were obtained at potentials >0.5 V. Transmission electron micrographs and X-ray diffraction pattern confirmed the difference in morphological features and growth of Pd dendrites. Pd deposited at 0.4 V showed higher electrochemical surface area of 128.5 m2 g−1 in comparison to 25.1 m2 g−1 obtained for Pd deposited at 0.5 V and also displayed enhanced activity towards formic acid oxidation.

Pd catalyst with dendritic morphology was synthesized on ordered and uniformly distributed titania nanotubes (TNT/Ti), and bare Ti by a simple electrochemical deposition process. The influence of support morphology was studied in relation to Pd deposition and its electro catalytic oxidation of formic acid. The structural property of Pd dendrites was characterized by scanning electron microscopy and X-ray diffraction. The electrochemical study showed the activity and durability of Pd/TNT/Ti catalyst for formic acid oxidation was enhanced compared to Pd/Ti electro catalyst. The synergetic contribution from TNT/Ti as support for Pd and its enhanced catalytic activity is discussed.

An air breathing direct methanol fuel cell (AB-DMFC) with a unique architecture was designed and fabricated to hold cell components together firmly, avoid fuel leakage and limit cell resistance. Pt and PtRu catalysts prepared by pulse electrodeposition on Ti mesh-based electrodes were employed and compared to traditional carbon-based electrodes. Results showed that Ti mesh can be a suitable catalyst support without the need for a gas diffusion layer (GDL) at the anode, while the absence of a GDL at the cathode drastically reduces cell performance, which can be attributed to the diffusion limitation of oxygen to the cathode. Among the various Ti mesh-based cell configurations explored, the optimum configuration was found with PtRu on an 80 mesh (47% open ratio) Ti anode and a Pt/C coated GDL with 40 mesh (71% open ratio) Ti as a cathode. The single cell AB-DMFC architecture was extended to 2-cell and 6-cell mini-stacks. The 6-cell stack, offering an OCV of 2.9 V and a maximum power of 60 mW using 2 M methanol and ambient air, was used to run a small portable device.

Fuel cells are a key enabling technology for the future economy, thereby providing power to portable, stationary, and transportation applications, which can be considered an important con-tributor towards reducing the high dependencies on fossil fuels. Electrocatalyst plays a vital role in improving the performance of the low temperature fuel cells. Noble metals (Pt, Pd) supported on carbon have shown promising performance owing to their high catalytic activity for both elec-troreduction and electrooxidation and have good stability. Catalyst preparation by electrodeposition is considered to be simple in terms of operation and scalability with relatively low cost to obtain high purity metal deposits. This review emphasises the role of electrodeposition as a cost-effective method for synthesising fuel cell catalysts, summarising the progress in the electrodeposited Pt and Pd catalysts for direct liquid fuel cells (DLFCs). Moreover, this review also discusses the technological advances made utilising these catalysts in the past three decades, and the factors that impede the technological advancement of the electrodeposition process are presented. The challenges and the fundamental research strategies needed to achieve the commercial potential of electrodeposition as an economical, efficient methodology for synthesising fuel cells catalysts are outlined with the necessary raw materials considering current and future savings scenario.

Palladium was electrodeposited on an electrochemically activated carbon black substrate using potentiostatic technique, with and without the addition of polyethylene glycol (PEG-6000) as an additive. Scanning electron micrographs showed change in morphology of Pd from spherical to flower, with increasing additive concentration. As an electrocatalyst for oxygen reduction reaction (ORR), formic acid oxidation and CO stripping, Pd nanoflowers displayed three- to fourfold increase in electrocatalytic activity in comparison to the spherical Pd deposits in terms of electrochemical surface area (ESA) and mass specific current density. X-ray diffraction (XRD) patterns showed, the introduction of additive with varying concentration effect the direction of Pd growth thereby changing the morphology from spherical to flower. The result demonstrates an increase in efficiency of Pd utilization achieved with the addition of PEG during electrodeposition, which could also be applicable to other precious metal electrocatalysts. A scheme for the change in Pd morphology during electrodeposition with additive is also proposed. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The product distribution of electrochemical reduction of CO2 can be altered by modifying the surface of pure copper by deposition. In this study, chronoamperometric deposition of Cu on Cu (Cu/Cu) was carried out at two different CuSO4 bath concentrations, 0.25 M (high) and 0.025 M (low), termed as Cu/Cu-H and Cu/Cu-L respectively. These deposits were characterized by X-ray diffraction and they vary in their crystal orientation. Pure Cu and Cu/Cu were aligned towards (1 1 1) and (2 2 0) plane with a texture coefficient of 1.2 and 1.7, respectively. Electrodeposited electrodes were tested for the electrochemical reduction of CO2 in KCl electrolyte and the results were compared with that of pure Cu electrode. Electrochemical reduction of CO2 showed methane and ethane, with hydrogen as the byproduct. The product distribution varied with the crystal orientation of Cu electrodes. The maximum Faradaic efficiency of methane was 26% obtained on pure Cu electrode with (1 1 1) and (2 0 0) orientation, whereas Cu/Cu-L with dominating (2 2 0) orientation showed a maximum formation of ethane with Faradaic efficiency of 43%. A possible mechanism of product formation on Cu towards C1 and Cu/Cu towards C2 is also discussed.

Engineering the shape and size of platinum catalysts is crucial in determining fuel cell performance. In this study, Pt electrodeposited on carbon black-coated carbon paper at three different potentials (viz. 0.2, 0, and −0.2 vs. SHE) was evaluated for its performance in direct formic acid fuel cells (DFAFCs). The electrodeposited catalysts were analysed using SEM, XRD, and electrochemical techniques. The shape of the electrodeposited Pt transformed from globular (0.2 V) to dendritic (0 V) and to rosette-like (−0.2 V) structure by increasing the deposition potential in the cathodic direction. The change in shape could be due to the variation in the accompanying hydrogen evolution with the deposition potential in acidic electrolyte. The dendritic structure of Pt deposited at 0 V showed a higher electrochemical surface area and enhanced catalytic activity towards formic acid oxidation than the other two shapes. To study the performance of electrocatalysts in DFAFC, the anode catalyst was prepared in a new approach of layer-by-layer electrodeposition on carbon to maximize the triple phase boundary. The layered dendritic Pt generated a maximum power density of 42 mW cm−2, comparable with the commercial Pt/C catalyst (46 mW cm−2) at 70 °C for 3 M formic acid. Graphical abstract: [Figure not available: see fulltext.].