Search

Abstract: A polymer electrolyte membrane water electrolyser (PEMWE) employing a segmented current collector made from a printed circuit board (PCB) with optical access to the channel has been demonstrated for the first time. The cell allows the local current density, flow regime and bubble formation dynamics to be studied in real time. Transition is observed from a flow of discrete bubbles at the start of the channel to long bullet shaped bubbles towards the end of the channel associated with a significant increase in local current density. [Copyright &y& Elsevier]

Understanding gas evolution and two-phase flow behaviour are critical for performance optimization of polymer electrolyte membrane water electrolysers (PEMWEs), particularly at high current densities. This study investigates the gas-bubble dynamics and two-phase flow behaviour in the anode flow-field of a PEMWE under different operating conditions using high-speed optical imaging and relates the results to the electrochemical performance. Two types of anode flow-field designs were investigated, the single serpentine flow-field (SSFF) and parallel flow-field (PFF). The results show that the PFF design yielded a higher cell performance than the SSFF design at identical operating conditions. Optical visualization shows a strong relationship between the flow path length and the length of gas slugs produced, which in turn influences the flow regime of operation. Longer flow path length in the SSFF results in annular flow regime at a high current density which degrades cell performance. The annular flow regime was absent in the PFF design. It was found the effect of flow rate on performance depends strongly on operating temperature in both flow patterns. Results of this study indicate that long channel length promotes gas accumulation and channel-blocking which degrades performance in PEMWEs. [ABSTRACT FROM AUTHOR]

Electrochemical power sources, such as polymer electrolyte membrane fuel cells (PEMFCs), require the use of precious metal catalysts which are deposited as nanoparticles onto supports in order to minimize their mass loading and therefore cost. State-of-the-art/commercial supports are based on forms of carbon black. However, carbon supports present disadvantages including corrosion in the operating fuel cell environment and loss of catalyst activity. Here we review recent work examining the potential of different varieties of graphitic carbon nitride (gCN) as catalyst supports, highlighting their likely benefits, as well as the challenges associated with their implementation. The performance of gCN and hybrid gCN-carbon materials as PEMFC electrodes is discussed, as well as their potential for use in alkaline systems and water electrolyzers. We illustrate the discussion with examples taken from our own recent studies. [ABSTRACT FROM AUTHOR]

The porous transport layer (PTL) in polymer electrolyte membrane water electrolysers (PEMWEs) has the multiple roles of delivering water to the electro-catalyst, removal of product gas, and acts as a conduit for electronic and thermal transport. They are, thus, a critical component for optimized performance, especially at high current density operation. This study examines the relationship between the microstructure and corresponding electrochemical performance of commonly used titanium sinter PTLs. Four PTLs, with mean pore diameter (MPD) ranging from 16 μm to 90 μm, were characterized ex-situ using scanning electron microscopy and X-ray computed micro-tomography to determine key structural properties. The performance of these PTLs was studied operando using polarization and electrochemical impedance spectroscopy. Results showed that an increase in mean pore size of the PTLs correlates to an increase in the spread and multimodality of the pore size distribution and a reduction in homogeneity of porosity distribution. Electrochemical measurements reveal a strong correlation of mean pore size of the PTLs with performance. Smaller pore PTLs showed lower Ohmic resistance but higher mass transport resistance at high current density of 3.0 A cm−2. A non-monotonic trend of mass transport resistance was observed for different PTLs, which suggests an optimal pore size beyond which the advantageous influence of macroporosity for mass transport is diminished. The results indicate that maximizing contact points between the PTL and the catalyst layer is the overriding factor in determining the overall performance. These results guide PTL design and fabrication of PEMWEs. • Four PTLs (MPD from 16 μm to 90 μm) were examined operando and ex-situ. • X-ray CT was used for 3D visualization and quantitative characterization. • Larger pore PTL showed lower mass transport resistance at high current density. • Best overall performance was found in smaller pore PTL. [ABSTRACT FROM AUTHOR]