Development of Raney-type Electrodes for Alkaline Water Electrolysis via Atmospheric Plasma Spraying

Kurzfassung

Hydrogen (H2) is regarded as the most promising energy carrier for the future with the potential to substitute fossil fuels. Its flexibility as energy carrier allows it to produce electricity via direct electrochemical conversion in fuel cells and it can also be used to produce heat through combustion which can later be used to produce work. In addition, H2 can be readily used to produce other energy carriers such as synthetic fuels and it is also fundamental in key industries such as in metallurgy and ammonia production. Even when H2 has been used industrially for decades, its current demand is met mainly through processing routes based on fossil fuels. For this reason, the development of cleaner and cost-effective routes for H2 production is one of the utmost active R&D topics around the world. The most promising of such routes is water electrolysis (WE). Within WE itself, different techniques have emerged, such as proton-exchange membrane water electrolysis (PEMWE), anion-exchange membrane water electrolysis (AEMWE), and alkaline water electrolysis (AWE). Among them, AWE exhibits higher potential for wide industrial deployment in short- to medium-term due to its maturity level and cost-effectiveness compared to AEMWE and PEMWE. However, more research is required to develop materials and processing methods to achieve higher durability and performance along with cost reductions. One strategy is the development of plasma spraying process for the fabrication of electrodes for AWE. Plasma spraying under atmospheric conditions (APS) has proven to be a low-cost, flexible technique suitable for the fabrication of Raney-type electrodes for AWE [1]. Its scalability capabilities also make it a great option for full research developments starting from lab-sized specimens, to full scale industrial electrodes. In this work, the development of AlNiMo Raney-type electrodes for the hydrogen evolution reaction (HER) in AWE produced via APS is presented. Electrodes are optimized through the control of different processing parameters and characteristics in order to reach the specific overpotential (oV) target of 75 mV at 0.5 A/cm2. For this, a first rough processing parameter window is sought to stablish a base line for next improvements. As shown in panel a) of figure 1, a reduction from 136 to 100 mV is reached through this rough approximation. Further studies include the effect of particle size distribution, where it was observed that the interlamellar porosity is an important feature of the performance of produced electrodes. Through the analysis of particle size distribution an oV value of 74 mV was obtained, thus fulfilling the initial target. Additional studies regarding the substrate type, the development of catalyst powders and the use of other special powder feedstock, allowed additional reductions to up to an oV value of -63 mV at 0.5 A/cm2, as depicted in panel b). Results demonstrate the feasibility of developing and optimizing electrodes for the HER in AWE via APS to values which are attractive for commercialization. Also, the observations made during this research, lead the way to future developments for these and other components used in WE.