Maksudul Hasan

The direct oxidation reaction of glycerol (GOR) was studied and compared to that of methanol (MOR) and ethanol (EOR) in both acid and alkaline media using commercial Pt/C, PtRu/C, Pd/C and PdNi/C electrocatalysts. The results show that GOR and MOR in alkaline media is better than that in acid media, in contrast to ethanol. Among the studied catalysts, PtRu/C showed the lowest onset potential and the highest catalytic activity for GOR and MOR in alkaline media, providing the lowest onset potential and a Tafel slope (TS) of 63 mV dec⁻¹, which could be attributed to the high surface poisoning tolerance. In fuel cells, the open circuit voltage of alkaline anion exchange membrane fuel cells (AEMFCs) was higher than that of the proton exchange membrane fuel cells (PEMFCs). In the kinetic region (up to 20 mA cm⁻²), the power density and cell performance were higher for AEMFCs than those of PEMFCs. However, the power density peaks were higher for PEMFCs than those for AEMFCs. Both the cell performance and the power density increased with increasing temperature. Regardless of the temperature and the media, glycerol crossover is comparable to that of ethanol but much less than that of methanol.

The capture and storage of solar energy in the molecular bonds of chemical fuels provides a promising route to overcoming the current global energy dependence on fossil fuels. Solar assisted water splitting, the process usually known as artificial photosynthesis, is a favourable means of converting solar energy into transportable and end user chemical fuels. The system requires optimisation in terms of cost and performance on a scale commensurate with the global energy demand. However, most abundant semiconductors suffer from the undesirable photoelectron-hole recombination within the semiconductor due to their short diffusion path lengths and lifetimes, which results in fewer than 10% of the incident photons being used for water splitting. Hematite (α-Fe₂O₃), one of the few naturally occurring n-type metal oxides, is the most promising candidate for an efficient photoanode because of its high earth abundance (4^th most abundant element in the earth’s crust) and visible light active band gap of 2.1 eV, a scalable CMOS compatible synthesis technique, excellent photostability and favourable energy band position capable to drive off the water oxidation reactions without of any external bias. Despite having those advantages, hematite has several inherent drawbacks such as poor electron mobility (~ 10^-1 cm² V^-1 s^-1)^[1], short excited carrier lifetime (about 10 ps)^[2] and short carrier (hole) diffusion length (2−4 nm)^[3]. Hence, most of the photogenerated charge carriers (electron-hole) cannot be extracted to the semiconductor-electrolyte interface before they quickly recombine inside of the materials and dissipate as heat energy. Nanoscale design of hematite such as nanowires^[4], cauliflowers^[5] or core-shell nanostructures synthesised via solution based hydrothermal growth and expensive chemical vapour deposition or atomic layer deposition^[6] along with surface modification with oxygen evolution catalysts^[5] have led to circumvent their drawbacks and made the nanostructured hematite a promising photoanode. In this work, electrochemical deposition of nanoporous α-Fe₂O₃ and surface modification with cobalt (Co) catalyst is described. The method involves the electrodeposition of iron (Fe) nanoporous film followed by thermal annealing in air (Fig. 1a). The kinetics of the photoelectrochemical (PEC) reactions was improved by modifying the hematite surface with oxygen evolution catalysts. The PEC activity of the optimised nanoporous α-Fe₂O₃/Co has been correlated with the morphology, thickness and Co loading under standard operational conditions (Am 1.5 G, 100 mW/cm², 1 mol/L KOH). This presentation will also discuss our current research to develop cheap and efficient photocatalysts towards fabrication of tandem PEC water splitting device. Figure. SEM images of the electrodeposited nanoporous hematite (α-Fe₂O₃) in (a) low and (b) high magnified view. Acknowledgements: Authors acknowledge Marie Curie Actions co-funded Irish Research Council Elevate fellowship ELEVATEPD/2014/15. References: [1] A. J. Bosman, H. J. Vandaal, Advances in Physics 1970, 19, 1-117. [2] N. J. Cherepy, D. B. Liston, J. A. Lovejoy, H. M. Deng, J. Z. Zhang, Journal of Physical Chemistry B 1998, 102, 770-776. [3] J. H. Kennedy, K. W. Frese, Journal of the Electrochemical Society 1978, 125, 709-714. [4] L. S. Li, Y. H. Yu, F. Meng, Y. Z. Tan, R. J. Hamers, S. Jin, Nano Letters 2012, 12, 724-731. [5] A. Kay, I. Cesar, M. Gratzel, Journal of the American Chemical Society 2006, 128, 15714-15721. [6] Y. J. Lin, S. Zhou, S. W. Sheehan, D. W. Wang, Journal of the American Chemical Society 2011, 133, 2398-2401. Figure 1

Synthesis of low‐dimensional metallic nanoparticles with a clean surface, high dispersibility, and enhanced atomic surface distribution is extremely important, as these factors strongly influence the electrocatalytic properties of the nanoparticles. In this study, the early stage electrochemical nucleation and growth of palladium nanoparticles (Pd NPs) under potentiostatic control has been investigated on a Au(111) textured substrate. The size distribution and structural characterization of the ex situ as‐deposited Pd NPs by means of high‐resolution field emission gun‐scanning electron microscopy (FEG‐SEM) at different stages combined with electrochemical measurements revealed that the cluster of nuclei grew independently through the reduction of metal ions. The electrodeposited Pd NPs were very pure, as confirmed by X‐ray photoelectron spectroscopy (XPS), owing to the surfactant‐free green electrodeposition process, and they exhibited a highly dispersed average particle size of 2–5 nm. The average nanoparticle size becomes smaller with higher overpotentials for the same deposition time. The synthesized Pd NPs demonstrated the largest specific surface area (four times that of commercial Pd−C) and electrocatalytic activity in ferrocyanide/ferricyanide redox and ethanol electrooxidation processes (35 times that of commercial Pd−C). This work represents an important step in achieving the fundamental understanding of nucleation and growth of nanoparticles correlating the electrocatalytic performances.

In this work, electrochemical deposition of Pd and bimetallic Pd−Ni nanoparticles on an oxygen‐terminated boron‐doped diamond (BDD) substrate is described for use as an electrocatalyst in a direct ethanol fuel cell. A potentiostatic two‐step electrochemical method involving the electrodeposition of Ni nanoparticles on BDD followed by mono‐dispersed Pd nanoparticles was used for the fabrication of a Pd−Ni/BDD electrode. The electrocatalytic activity of the bimetallic Pd−Ni nanoparticles was evaluated in an alkaline solution containing ethanol and compared to that of the Pd nanoparticles alone. The bimetallic Pd−Ni nanoparticles showed 2.4 times higher mass activity than similar systems in the literature as well as stability when operated in alkaline media. The higher electrochemical response towards the electrooxidation of ethanol observed for the bimetallic electrocatalysts was attributed to the synergistic effects of the electron interaction at the interface of the two metals. Chronopotentiometric measurements revealed that Pd is more stable when anchored to the Ni nanoparticles. The optimised loading of mono‐dispersed Pd on a foreign Ni metal as nanoparticles plays a crucial role in achieving a high mass (3.63×10⁶ mA/g) and specific (10.53 mA/cm²) electrocatalytic activity of Pd towards ethanol electrooxidation in alkaline media.

It is generally accepted that one of the main challenges facing our planet today is the human interfered climate change and its inseparable link to our global society’s present and future needs. Solar energy is doubtless one of the most attractive ways to deal with these issues. Water splitting by artificial photosynthesis is a favourable means of converting solar energy into transportable and end user chemical energy. Two of the major issues that remain unresolved in artificial photosynthesis are first to find a visible light absorber earth abundant semiconductor and second a robust substrate. Additionally, photon to current conversion efficiency of the current state-of-the-art semiconductor is far below the theoretical value due to undesirable charge carrier recombination loses. Cuprous oxide (Cu₂O) is a naturally occurring p-type metal oxide semiconductor, is abundant and promisingly possesses a suitable band gap (2.0 eV) and energy band position that enable it to absorb solar light in the visible spectrum to produce hydrogen gas without external bias. However, Cu₂O suffers from rapid charge carrier recombination losses and self-photocorrosion when comes in contact with water under illumination. The use of bimetallic alloys or core-shell metals in nanoparticle format is beneficial in two ways; protecting semiconductor from self-photo corrosion and providing short diffusion paths for electron-hole pairs enabling fast transfer to the respective redox reaction sites. Boron-doped diamond (BDD) is a potential substrate in the field of electrocatalysis due to its plethora of advantages such as wide potential window, low background current, resistance to fouling and electrocorrosion as well as its availability at a low cost when grown by chemical vapour deposition (CVD). In this work, the electrochemical modification of oxygen terminated boron doped diamond (OBDD) electrodes decorated with NiO-Cu₂O nanoparticles is described. The method involves the electrodeposition of Cu₂O nanoparticles on OBDD from a surfactant-free electrolyte followed by a thin coating of NiO onto Cu₂O nanoparticles (Fig. 1a). The electrochemical experimental data showed that electronic effects due to the bimetallic catalysts led to higher photocurrent densities in comparison with Cu₂O nanoparticles alone (Fig. 1b). In order to understand the morphology, dispersity and size of the nanoparticles, deposits were characterised by high resolution scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Figure 1 (a) SEM image of NiO-Cu₂O modified OBDD electrode and (b) Linear-sweep voltammograms of the photoelectrochemical response of Cu₂O and NiO-Cu₂O modified OBDD electrodes, respectively under chopped light (100 mW cm^-2 and on-off frequency 0.2 Hz) at a scan rate of 10 mV s^-1 in 0.1 M Na₂SO₄ (pH 6.2). Figure 1

Sustainable ‘green’ energy applications have received increasing research efforts in the last few years to deal with issues such as climate change, energy shortage and environmental pollution. A subcategory of fuel cells, the direct alcohol fuel cells (DAFCs) have been established in that field due to their ability to convert the chemical energy stored in the fuel into electricity and can be utilised in portable devices and transportation applications. Electrocatalysis is an important aspect in the development of such sustainable technologies. Hybrid materials consisting of graphitic nanostructures and various metal or metal oxide complexes have been widely studied as functional components in catalysis for fuel cell applications. The development core-shell nanostructures and replacing or reducing noble metal content by the incorporation of non-noble metals promises to increase the overall mass activity and improve stability due to electronic interactions with the interfacial layer in the inner shell. Herein, the electrodeposition of Ni and Pd nanoparticles supported on oxygen terminated boron-doped diamond (OBDD) electrodes is described. The electrochemical modification involves two-steps; first electrodeposition of Ni as nanoparticles on OBDD followed by Pd onto the freshly deposited Ni nanoparticles. SEM imgage of the sequential deposition of Pd-Ni produced nanoparticles in the size range of 10-13 nm is shown in Fig. 1 (a). XPS and electrochemical characterization showed that Ni nanoparticles act as reactive centres on OBDD for the subsequent deposition of Pd to form core-shell nanostructures. The Pd-Ni/OBDD electrocatalysts were evaluated in an alkaline aqueous solution containing ethanol and compared to Pd/OBDD itself. The formation of core-shell nanostructures led to high current responses for ethanol oxidation. The phenomenon is attributed to the improved dispersion of Ni onto the BDD and the electronic interaction between the interfaces of the two metals. Of note is the fact the core-shell catalysts exhibited enhanced mass activity and operational stability. After chronopotentiometric measurements, there was only 12% current drop of the Pd-Ni/OBDD in comparison to 35% current drop of the Pd/OBDD catalyst itself. The Pd-Ni electrocatalysts even with 4 times less palladium loading showed higher amperometric response than the pure Pd/OBDD (Fig. 1(b)). The higher mass activity is likely due to an increased tolerance to carbon based reaction by-products poisoning effects at the bimetallic interface with the transition metal in the inner shell. Figure 1 (a) SEM image of Pd-Ni modified OBDD electrode (b) Cyclic voltammograms of Pd and Pd-Ni modified OBDD in 0.5 M KOH and 1 M EtOH at a potential scan rate of 100 mV s^-1. Figure 1