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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% CH 4 and 30% H 2 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 (O O). Many studies under the initial research stage report using Ni–CeO 2 as a promising catalyst toward OER, observing good catalytic activity and stability at low overpotentials. This work deposited electrodes with Ni and Ni–CeO 2 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–CeO 2 electrodes than Ni electrodes was obtained. Ni–CeO 2 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–CeO 2 showed instability and high overpotentials as 500 h were completed. The last is attributed to the low conductivity of CeO 2 and the formation of the passive NiO/NiOH 2 layer on the electrode surface, which is not easily detached due to the presence of CeO 2. These results confirm the importance of conducting tests in an electrolyser under real conditions. • A better OER electrocatalytic activity of modified Ni–CeO 2 electrodes was obtained. • Ni electrode showed electrochemical stability after 500 h under operation conditions in an alkaline electrolyser. • Ni–CeO 2 electrode showed electrochemical instability and high overpotentials after 500 h. • Passive NiO/Ni(OH) 2 layer on the Ni–CeO 2 electrode is not easily detached to the presence of CeO 2. [ABSTRACT FROM AUTHOR]

In this study, we report a highly flexible and biodegradable supercapacitor (SC) assembled with electrodes made of cellulose and graphene microplates. The cellulose was extracted from the palocote plant (tithonia tubaeformis), which is considered a weed in Mexico. To enhance the capacitance of the devices, Ca 2.9 La 0.1 Co 4 O 9 (CaLaCo) particles with microplate morphology were added to the SC electrodes. The electrochemical characterization indicated that the SCs fabricated without CaLaCo particles exhibited a specific capacitance of 777.3 F/g (at 1 A/g) and an energy density of 108.1 Wh/kg. When the CaLaCo was introduced into the SC electrodes, the above parameters increased to 1320.3 F/g (at 1 A/g) and 182.3 Wh/kg, that is, the capacitive performance was enhanced by ≈ 70%. Also, the device made with the CaLaCo particles exhibited a high capacitance retention of 95.8% after 1500 continuous charging/discharging cycles. Some advantages in the devices made with CaLaCo in comparison with these fabricated without CaLaCo were: 1) longer discharge times and 2) low loss of capacitance (4.1%) at higher current densities (up to 10 A/g). On the other hand, redox peaks were observed in the cyclic voltammetry curves, suggesting the storage of charge by redox reactions. To find the redox centers responsible for the charge storage, optical absorbance, Raman and XPS measurements were carried out and we found that the oxygen vacancy defects and Co2+/Co3+ species were the main redox centers. Furthermore, EIS measurements showed that the series resistance (R s) and charge transfer resistance (R ct) decreased by 28% and 80%, respectively, after the introduction of the CaLaCo oxide in the SC. The reduction of the R s and R ct was relevant because it promoted the ion diffusion/storage in the electrodes, which in turn, increased the capacitance of the devices. Thus, the results of this report indicate that our biodegradable and flexible SC could be produced from sustainable materials and can be used as energy source for wearable/portable devices. [Display omitted] • Supercapacitors (SCs) were made from cellulose extracted from weed plant. • Adding the Ca 2.9 La 0.1 Co 4 O 9 (CaLaCo) oxide in the SCs enhanced their capacitance by 70%. • The initial capacitance was reduced only 4.2% after 1500 charging/discharging cycles. • Oxygen vacancies and Co2+/Co3+ species were the redox centers for the charge storage. [ABSTRACT FROM AUTHOR]