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Common carbon-blacks have shown insufficient stability as cathodic catalyst supports for proton exchange membrane fuel cells (PEMFCs). In this regard, alternative supports have been proposed and, specifically graphene or reduced graphene oxide (rGO), have attracted special attention. Herein, a set of electrocatalysts using reduced graphene oxide (rGO) as support is synthetized by a modified polyol method. The influence of Pt loading on the support is studied and compared with conventional supports, considering Pt particle morphologies and oxygen reduction reaction (ORR) performance in rotating disk electrode (RDE). Despite Pt average particle size typically increases with the Pt loading, 30 wt% of Pt on rGO is the optimal Pt loading, yielding the highest ORR activity among the rGO-supported electrocatalysts. These results show that both Pt loading and type of support greatly impact on the morphology and electrochemical performance of Pt nanoparticles.

Planet Earth is facing accelerated global warming due to greenhouse gas emissions from human activities. The United Nations agreement at the Paris Climate Conference in 2015 highlighted the importance of reducing CO2 emissions from fossil fuel combustion. Hydrogen is a clean and efficient energy carrier and a hydrogen-based economy is now widely regarded as a potential solution for the future of energy security and sustainability. Although hydrogen can be produced from water electrolysis, economic reasons dictate that most of the H2 produced worldwide, currently comes from the steam reforming of natural gas and this situation is set to continue in the foreseeable future. This production process delivers a H2-rich mixture of gases from which H2 needs to be purified up to the ultra-high purity levels required by fuel cells (99.97%). This driving force pushes for the development of newer H2 purification technologies that can be highly selective and more energy efficient than the traditional energy intensive processes of pressure swing adsorption and cryogenic distillation. Membrane technology appears as an obvious energy efficient alternative for producing the ultra-pure H2 required for fuel cells. However, membrane technology for H2 purification has still not reached the maturity level required for its ubiquitous industrial application. This review article covers the major aspects of the current research in membrane separation technology for H2 purification, focusing on four major types of emerging membrane technologies (carbon molecular sieve membranes; ionic-liquid based membranes; palladium-based membranes and electrochemical hydrogen pumping membranes) and establishes a comparison between them in terms of advantages and limitations.

The use of single wall nanohorns (SWNH) as electrocatalyst support has proved to increase the performance of polymer electrolyte membrane-based fuel cells. In order to investigate in more detail such behavior, the electrochemical characterization of SWNH based electrodes was performed. The use of SWNH in vapour phase high temperature direct methanol fuel cells (HT-DMFC) was also addressed. Cyclic voltammetry experiments have indicated a higher electrochemical activity towards methanol electro-oxidation and a higher tolerance to carbonaceous species accumulation for a SWNH based electrode than for carbon black and commercial corresponding ones. Carbon black electrode presented a better performance than SWNH one for oxygen reduction reaction at low current densities while, at higher overvoltages, SWNH electrode performed better. The exact role of the improved performance of SWNH based electrodes is yet not clear but may be related to a higher water vapour adsorption or electrode morphology. Vapour phase HT-DMFC operation showed the improved performance of the SWNH electrode in agreement with previous works and with the electrochemical characterization performed during this work; despite the higher ohmic resistance observed in comparison with the carbon black based electrode. Moreover, SWNH based electrode showed improved fuel cell stability during longer operation times.

The permeance of a 50 mm thick PdAg (25 wt.% of silver) tubular membrane towards hydrogen was evaluated for hydrogen feed streams or binary mixtures of industrial relevance, namely of H2/CO or H2/CO2. It was proposed a rearrangement of the SievertseLangmuir (SL) equation to account for the inhibition effect on the membrane permeance towards H2 due to the presence of CO or CO2. Such modification is based on the average partial pressure of CO or CO2 and the logarithm-mean driving-force to account for concentration gradients along the axial length of the tubular membrane. Comparison with the original SL equation evidenced relative deviations < 10.7%. The experimental data showed good agreement with the SL model. It was found that carbon monoxide has a much stronger inhibition effect on hydrogen permeation than carbon dioxide. Considering the values obtained for the adsorption enthalpy of each gas, it was concluded that both CO and CO2 adsorb physically on the membrane surface.