Thin film-rotating disc electrode (TF-RDE) experiment provides a fast research platform for screening of newly developed electrocatalysts for oxygen reduction reaction (ORR) activity, however, precise estimation of their performance parameters is necessary to avoid wastage of resources in the testing of otherwise unpromising electrocatalyst in actual fuel cells. Here we show the importance of the accurate amount of catalyst (e.g. Pt) on glassy carbon (GC) disk of RDE in TF-RDE experiment by characterizing the commercial catalysts for their electrocatalysis performance (electrochemical surface area and ORR activity) values. The Pt loadings used to calculate these performance values were obtained using two schemes, namely, using the literature based (conventional) scheme and an X-ray fluorescence (XRF) based scheme. A parameter called 'catalyst-density-ofthe-ink' is used to correlate the variations observed in performance values and the amount of Pt on GC disk of RDE obtained using both the schemes. The investigation suggests that the actual Pt loading on GC disk of RDE varies with the ink-conditions, which is considered constant in the conventional scheme and might be one of the reasons of irreproducibility of the data obtained by TF-RDE experiments. The XRF based scheme, which is simple and direct, can have the potential to replace conventional scheme for accurate catalyst loading estimation, improve experimental reproducibility and open many other possibilities (e.g. postmortem analysis of catalyst) in electrocatalysis studies.

Iridium based materials are the state-of-the-art anode catalysts for polymer electrolyte membrane (PEM) water electrolysis thanks to their unmatched stability and performance in the acidic environment of common PEMs like Nafion®. However, their uses on a large-scale operation are cost-restrictive. To improve their wider utilization, identifying a synthesis method of nano-structured iridium oxide with high active surface area, possibly in a supported-form, is of great importance. For this aim, we developed a one-step and cost-effective solution combustion synthesis (SCS) method to prepare nano-structured IrO2 and IrO2-based materials suitable for PEM electrolysis. Among various materials prepared, the iridium oxide incorporated and dispersed in amorphous alumina showed high surface area (131 m 2 g -1 ) and the current density of 1.78 A cm -2 at 1.8 V which is comparable to the performance of the state-of-the-art commercial MEA made of IrRuOx (1.8 A cm -2 at 1.8 V) under PEM water electrolysis. Importantly, the dispersion of the material in the catalyst ink used for the preparation of membrane electrode assembly (MEA) was significantly superior compared to commercial IrO2 nanoparticles and the amount of the precious metal in the catalyst made by SCS could be reduced by 45 wt% compared to that in the commercial MEA. IntroductionHydrogen has been considered as chemical energy carrier alternative to fossil fuels over the past decades. Hydrogen has the potential to provide clean, reliable and affordable energy supply to meet the growing global energy demand. 1-3 Apart from being a clean fuel yielding water as only byproduct upon combustion, hydrogen can be produced using natural and renewable energies 4 and then it can readily be used in fuel cells 5-7 to produce clean power for variety of applications. This energy pathway could serve as one of the solutions to sustainable energy supply. Among various approaches, a promising method to produce highly pure hydrogen is by electric potential induced water splitting (water electrolysis). 1 In a conceptual distributed energy production, conversion, storage and use system, e.g. for off-grid locations, water electrolysis can play pivotal roles (Section S1.1 and Figure S1, electronic supporting information -ESI). 2 Two major reactions take place during electrochemical water splitting: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Among the two, OER is considerably more energy demanding and is the major contributor to the energy losses due to the higher overpotential of OER in water electrolysis. The most active electrocatalysts known to date for OER are IrO2 and RuO2. [8][9][10] IrO2 exhibits high corrosion resistance with slightly less activity compared to RuO2. 9 Furthermore, the standard amount of loading of IrO2 (or IrRuOx) is rather high (~3 mg cm -2 ), hampering the commercialization of polymer electrolyte membrane (PEM) water electrolysis on a large scale. Therefore, to enhance the activity of IrO2 and to reduce the precious metal loading (Secti...

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