Influence of CeO2 nanoparticles in the stability of electrodeposited Ni anodes for alkaline electrolysers

Abstract

In Mexico, the National Electric System Development Program (PRODESEN 2022–2036) establishes the use of green hydrogen to be supplied in Combined Cycle Power Plants in a mixture of 70% CH4 and 30% H2 for electric energy generation. For those places where natural resources such as sun, wind, and water are available, the best option is to use alkaline electrolysers due to cost and lifetime. The oxygen evolution reaction (OER), which takes place at the anode, is the limiting factor in the performance of an alkaline electrolyser because large overpotentials are required to break the (O–H)- bond needed to form the double bond of the gaseous oxygen molecule (OO). Many studies under the initial research stage report using Ni–CeO2 as a promising catalyst toward OER, observing good catalytic activity and stability at low overpotentials. This work deposited electrodes with Ni and Ni–CeO2 films of 80 μm on AISI 304 Stainless steel substrates.A kinetic study was performed using linear sweep voltammetry to determine the Tafel slope of the OER. An electrolysis system was integrated with these anodic electrodes and tested for 500 h to determine the stability of films at real operating conditions using 15 wt% NaOH as electrolyte @ 0.5 A cm−2. A better OER activity of the modified Ni–CeO2 electrodes than Ni electrodes was obtained. Ni–CeO2 electrode shows an onset potential of 1.48 V, a potential of 1.56 V at 5 mA cm−2, and a Tafel slope of 75.71 mV dec−1, which is related to a reaction determining step in an oxidation process of (OH)− via the one-electron transfer to the surface which is partial cover by OH species adsorbed. In the studies with the electrolyser test system, the Ni electrodes with an electrodeposited film of 80 μm showed good stability, and the film remained on the surface electrode.On the other hand, the electrode modified with Ni–CeO2 showed instability and high overpotentials as 500 h were completed. The last is attributed to the low conductivity of CeO2 and the formation of the passive NiO/NiOH2 layer on the electrode surface, which is not easily detached due to the presence of CeO2. These results confirm the importance of conducting tests in an electrolyser under real conditions.