Shape-Dependent Electrocatalysis: Oxygen Reduction on Carbon-Supported Gold Nanoparticles

Cubic, octahedral and quasi-spherical (two different particle sizes) Au nanoparticles are synthesised and dispersed in a carbon-black powder. The size and morphology of the Au nanocatalysts is confirmed by transmission electron microscopy and X-ray diffraction. Au nanospheres are approximately 5 and 30 nm in diameter, whereas the size of Au octahedra and nanocubes is approximately 40–45 nm. The electrocatalytic activity of these carbon-supported particles towards the oxygen reduction reaction (ORR) is studied in 0.5 M H2SO4 and 0.1 M KOH solutions by using the rotating-disk-electrode method. The specific activity (SA) for O2 reduction is measured, and the highest SA is observed for Au nanocubes supported on carbon. The highest mass activities are found for the smallest Au nanoparticles. Tafel analysis suggests that the mechanism of the ORR on shape-controlled Au/C catalysts is the same as on bulk Au.This research was financially supported by institutional research funding (IUT 20–16) of the Estonian Ministry of Education and Research and by the Estonian Research Council (Grant No. 8380), by Archimedes Foundation (Project No. 3.2.0501.10–0015), by the MCINN-FEDER (Spain) (project CTQ 2010–16271) and by the Generalitat Valenciana (project PROMETEO/2009/045)

PdPt alloy nanocubes as electrocatalysts for oxygen reduction reaction in acid media

In this work, PdPt alloy nanocubes with different metal ratios were synthesised in the presence of polyvinylpyrrolidone (PVP). The surface morphology of the PdPt samples was characterised by transmission electron microscopy (TEM). TEM images showed that PdPt nanoparticles were cubic-shaped and the average size of the cubes was about 8–10 nm. Their electrocatalytic activity towards the oxygen reduction reaction (ORR) was studied in 0.5 M H2SO4 using the rotating disc electrode method. All the alloyed catalysts showed enhanced electrocatalytic activity for ORR as compared to the monometallic cubic Pd nanoparticles. Half-wave potential values for PdPt catalysts were comparable with that of Pt nanocubes. From the alloyed catalysts Pd36Pt64 exhibited the highest specific activity, which was only slightly lower than that of cubic Pt nanoparticles. The Koutecky–Levich analysis revealed that the reduction of oxygen proceeded via 4-electron pathway on all the electrocatalysts studied.This research was financially supported by institutional research funding (IUT20-16) of the Estonian Ministry of Education and Research and by the Estonian Research Council (Grant No. 9323) and by Archimedes Foundation (Project No. 3.2.0501.10-0015). KJ thanks the Archimedes Foundation for scholarship. JMF acknowledges financial support from MINECO (Spain), project CTQ2013-44083-P

Recent progress in oxygen reduction electrocatalysis on Pd-based catalysts

Palladium-based catalysts for electrochemical reduction of oxygen have received increasing attention as potential replacement for platinum-based materials in the fuel cells. This Review summarises the research conducted with nanostructured palladium catalysts, including thin nanostructured films and Pd nanoparticles on various carbon and non-carbon supports. The mechanism of oxygen reduction on palladium is described and the effect of the particle size and shape on the electrocatalytic activity is emphasised. The role of the support material and additives on the oxygen reduction activity of Pd nanoparticles is also discussed. The electrocatalytic activity of Pd-based catalysts is evaluated in terms of specific activity and mass activity. The application of supported Pd nanoparticles as cathode catalysts for low-temperature fuel cells is highlighted. Some insights into the remaining challenges and directions for further development of Pd-based oxygen reduction electrocatalysts are provided.This work was financially supported by institutional research funding (IUT20-16) of the Estonian Ministry of Education and Research. We would like to acknowledge the financial support by the EU through the European Regional Development Fund (TK141 “Advanced materials and high-technology devices for energy recuperation systems”)

Oxygen reduction reaction on carbon-supported palladium nanocubes in alkaline media

Carbon-supported Pd nanocubes with the size of 30, 10 and 7 nm were prepared and their electrocatalytic activity towards the oxygen reduction reaction (ORR) in alkaline solution was studied. For comparison carbon-supported spherical Pd nanoparticles and commercial Pd/C catalyst were used. The catalysts were characterised by transmission electron microscopy, electro-oxidation of carbon monoxide and cyclic voltammetry and the ORR activity was evaluated using the rotating disk electrode method. The ORR on all studied Pd/C catalysts proceeded via four-electron pathway where the rate-limiting step was the transfer of the first electron to O2 molecule. The specific activity of Pd nanocubes was more than two times higher than that of spherical Pd nanoparticles and increased with increasing the particle size.This research was financially supported by institutional research funding (IUT20-16) by the Estonian Ministry of Education and Research and by the Estonian Research Council (Grant No. 9323)

Oxygen electroreduction on carbon-supported Pd nanocubes in acid solutions

The oxygen reduction reaction (ORR) was studied on carbon-supported cubic palladium nanoparticles of different sizes (∼30 nm, ∼10 nm and ∼7 nm). Cetyltrimethylammonium bromide (CTAB) and polyvinylpyrrolidone (PVP) were used as capping agents to prepare the nanocubes and Pd content in the catalyst samples was 20 and 50 wt%. The surface morphology of the prepared materials was studied by transmission electron microscopy (TEM). The catalyst materials were electrochemically characterised by cyclic voltammetry and CO stripping experiments. The rotating disk electrode (RDE) method was employed for ORR studies in 0.5 M H2SO4 and 0.1 M HClO4 solutions. The ORR results revealed that the specific activity of cubic Pd nanoparticles is higher than that of spherical Pd particles and does not depend on the Pd content in the catalyst, but decreases with decreasing the size of Pd nanocubes. Mass activity of Pd nanocubes increased with decreasing the particle size. The ORR proceeds mainly via 4-electron pathway and the reaction mechanism is similar to that on bulk Pd.This research was financially supported by institutional research funding (IUT20-16) of the Estonian Ministry of Education and Research and by the Estonian Research Council (Grant No. 9323). HE thanks the Archimedes Foundation for scholarship. JMF acknowledges financial support from MINECO (Spain), project CTQ2013-44083-P

Loading effect of carbon-supported platinum nanocubes on oxygen electroreduction

In this work, Vulcan carbon-supported cube-shape Pt nanoparticles with various metal loadings were synthesised in the presence of oleylamine and oleic acid. Surface morphology of different Pt/C samples was examined by transmission electron microscopy (TEM) and their metal loading verified by thermogravimetric analysis (TGA). TEM micrographs showed Pt nanoparticles with a preferential cubic-shape and increased agglomeration of the particles with increasing Pt loading. Electrochemical characterisation of the Pt/C catalysts indicated that the resulting Pt nanoparticles present a preferential (100) surface structure. The electrocatalytic properties of the Pt/C catalysts of different metal loading were evaluated towards the oxygen reduction reaction (ORR) both in acidic and alkaline media employing the rotating disk electrode (RDE) configuration. Interestingly, similar specific and mass activities were found in both solutions revealing that the ORR activities were independent of the Pt loading and suggesting that all the Pt nanocubes contributed as isolated particles.This work was financially supported by institutional research funding (IUT20-16) of the Estonian Ministry of Education and Research. This research was also supported by the EU through the European Regional Development Fund (TK141 “Advanced materials and high-technology devices for energy recuperation systems”). KJ would like to thank Archimedes Foundation for the partial study scholarship. JMF thanks MINECO (Project CTQ2016-76221-P (AEI/FEDER, UE)) and Generalitat Valenciana (Project PROMETEOII/2014/013) for financial support. JSG acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante