Synthesis and characterization of titanium dioxide based ternary nanocomposites for photocatalytic hydrogen production

Titanium dioxide based photocatalysts of different graphene oxide (GO) and silver nanoparticle (AgNP) content were prepared and tested in catalytic methanol reformation reaction. Aqueous suspensions of the composite solids obtained by heterocoagulation of alkaline exfoliated GO suspension and slightly acidic TiO2 suspension showed enhanced sedimentation rate at pH = 6.5- 7, when they contained less than 2 wt% graphene oxide. This enables easier catalyst recovery but the suspension needs to be stirred strongly during the catalytic run in order to achieve homogeneous light distribution within the reaction vessel. The catalytic runs were performed in 6 V/V% methanol/water mixture using 500 mg/L catalyst under UV-illumination. The activity of pure titanium dioxide (Degussa P25) continuously increases and reaches a saturation plateau after 150 min with an activity of 0.12 mmol H2/(h×gcat). Incorporation of GO into the titanium dioxide matrix by heterocoagulation method results in aggregated suspensions exhibiting an enhancement of the hydrogen evolution rate to the saturation value of 0.17 mmol H2/(h×gcat). Deposition of different amounts of AgNPs of different sizes onto the surface of titanium dioxide resulted in an even higher photocatalytic activity, reaching 0.25-0.29 mmol H2/(h×gcat). The combination of AgNP’s and GO platelets to obtain ternary TiO2 based catalysts has not shown any further increase of hydrogen generation rate

Insights into the Influence of Different Pre-Treatments on Physicochemical Properties of Nafion XL Membrane and Fuel Cell Performance

Perfluorosulfonic acid (PFSA) polymers such as Nafion are the most frequently used Proton Exchange Membrane (PEM) in PEM fuel cells. Nafion XL is one of the most recently developed membranes designed to enhance performance by employing a mechanically reinforced layer in the architecture and a chemical stabilizer. The influence of the water and acid pre-treatment process on the physicochemical properties of Nafion XL membrane and Membrane Electrode Assembly (MEA) was investigated. The obtained results indicate that the pre-treated membranes have higher water uptake and dimensional swelling ratios, i.e., higher hydrophilicity, while the untreated membrane demonstrated a higher ionic exchange capacity. Furthermore, the conductivity of the acid pre-treated Nafion XL membrane was ~ 9.7% higher compared to the untreated membrane. Additionally, the maximum power densities obtained at 80 °C using acid pre-treatment were ~ 0.8 and 0.93 W/cm2 for re-cast Nafion and Nafion XL, respectively. However, the maximum generated powers for untreated membranes at the same condition were 0.36 and 0.66 W/cm2 for re-cast Nafion and Nafion XL, respectively. The overall results indicated that the PEM’s pre-treatment process is essential to enhance performance

Development of WO3–Nafion Based Membranes for Enabling Higher Water Retention at Low Humidity and Enhancing PEMFC Performance at Intermediate Temperature Operation

The proton exchange membrane (PEM) represents a pivotal material and a key challenge in developing fuel cell science and hydrogen technology. Nafion is the most promising polymer which will lead to its commercialisation. Hybrid membranes of nanosized tungsten oxide (WO3) and Nafion were fabricated, characterised, and tested in a single cell. The incorporation of 10 wt% WO3 resulted in 21% higher water uptake, 11.7% lower swelling ratio, almost doubling the hydration degree, and 13% higher mechanical stability of the hybrid membrane compared to the Nafion XL. Compared to commercial Nafion XL, the rNF–WO-10 hybrid membrane showed an 8.8% and 20% increase in current density of the cell at 0.4 V operating at 80 and 95 °C with 1.89 and 2.29 A/cm2, respectively. The maximum power density has increased by 9% (0.76 W/cm2) and 19.9% (0.922 W/cm2) when operating at the same temperatures compared to the commercial Nafion XL membrane. Generally, considering the particular structure of Nafion XL, our Nafion-based membrane with 10 wt% WO3 (rNF–WO-10) is a suitable PEM with a comparable performance at different operating conditions

Combinatorial design and preparation of transition metal doped MoVTe catalysts for oxidation of propane to acrylic acid

In this study Mo-V-Te-Nb based multi-component catalysts were designed and tested using combinatorial and high-throughput methods. Based on the composition of the M1 matrix phase new compositions were designed containing additional promoters Mn, Ni, W and In. The following promoters were tested too in preliminary experiments and disregarded because of the detrimental effect on acrylic acid yields: Cu, Sb, Fe, Sm, Sn, Bi, Co, and Cr. In addition, citric acid in different ratios was used in the synthesis as a structure-directing agent. An optimization variable has been defined as the molar ratio of a given component to Mo in the synthesis mixture. Consequently, the experimental space had eight variables. The discrete levels of variables are established in such a way that the size of the multi-dimensional experimental space was in the range of 200 000 theoretical experiments. Five generations were designed using an optimization platform consisting of artificial neural networks and holographic optimization algorithm. Altogether 215 catalysts were prepared and tested. The elite list in each generation was created according to the yield of acrylic acid (AA). The yield of AA over the best catalyst after five generations was 59%. On the basis of holographic maps correlations between the composition of the synthesis mixture and yield of AA were visualized. Two catalysts families amongst the good performing catalysts have been distinguished that differ from each other in their low and high V content as referenced to molybdenum. © 2013