Developing efficient, durable, and low cost catalysts based on earth-abundant elements for the 12 oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential for renewable energy 13 conversion and energy storage devices. We report herein a simple one-pot procedure for the synthesis of 14 non-precious metals N-doped graphene composites employing urea as nitrogen source, and their 15 application as bifunctional catalysts for both the ORR and OER in alkaline environment. In this study, the 16 effects of the addition of Ti and Co on the structure and performance of the N-doped graphene composites 17 are investigated. The incorporation of Ti leads to a composite with both anatase and rutile TiO 2 crystalline 18 phases as well as Ti 3+ species stabilized upon hybridization with N-doped reduced graphene oxide. The ORR 19 onset potential for the Ti-based composite is 0.85V (vs. RHE) and the number of electrons transferred is 20 3.5, showing superior stability than Pt/C after accelerated potential cycling in alkaline solution. However, 21 this composite shows low activity and stability for the OER. On the other hand, the composite consisting of 22 metallic Co and Co 3 O 4 nanocrystals grown on N-doped reduced graphene oxide exhibits the best 23 performance as bifunctional catalyst, with ORR and OER onset potentials of 0.95 V and 1.51 V (vs. RHE), 24 respectively, and a number of electrons transferred of 3.6 (ORR). The results reveal the presence of 25 important structural features such as metallic Co as the predominant crystalline component, amorphous 26 Co 3 O 4 phase and the coordination of Co-N-doped graphene. All of them seem to be fundamental for the 27 high activity and stability towards ORR and OER. 28 29 30 2 1. Introduction 31Oxygen reduction (ORR) and evolution (OER) reactions are undoubtedly the most important electrochemical 32 reactions associated with energy conversion and storage technologies, such as fuel cells or water 33 electrolyzers, and the combination of both systems: unitized regenerative fuel cells (URFCs) [1, 2]. However, 34 the sluggish kinetics of these reactions in acid environment at low temperature requires a large quantity of 35 precious metals (e.g. Pt, Ir or Ru) to enhance reaction activity and durability [3][4][5][6][7][8]. The utilization of anion 36 exchange membranes presents several potential advantages compared to its acidic Nafion-based 37 counterpart, including improved kinetics of electrochemical reactions, materials stability, and easy water 38 management [9][10][11][12]. Therefore, anion exchange membrane fuel cells and electrolyzers may hold great 39 potential in the near future, providing an opportunity to use a host of non-platinum group metal catalysts 40 [13]. Furthermore, anion exchange membranes unitized regenerative fuel cells (AEM-URFCs) have attracted 41 attention in recent years because they involve interconversions between H 2 , O 2 , and H 2 O in a single system 42 [14, 15]. AEM-URFCs possess high specific energy, enjoy economies-of-scale advant...

Polymer electrolyte fuel cells with alkaline anion exchange membranes (AAEMs) have gained increasing attention because of the faster reaction kinetics associated with the alkaline environment compared to acidic media. While the development of anion exchange polymer membranes is increasing, the catalytic layer structure and composition of electrodes is of paramount importance to maximize fuel cell performance. In this work, we examine the preparation procedures for electrodes by catalyst-coated substrate to be used with a well-known commercial AAEM, Fumasep® FAA-3, and a commercial ionomer of the same nature (Fumion), both from Fumatech GmbH. The anion exchange procedure, the ionomer concentration in the catalytic layer and also the effect of membrane thickness, are investigated as they are very relevant parameters conditioning the cell behavior. The best power density was achieved upon ion exchange of the ionomer by submerging the electrodes in KCl (isopropyl alcohol/water solution) for at least one hour, two exchange steps, followed by treatment in KOH for 30 min. The optimum ionomer (Fumion) concentration was found to be close to 50 wt%, with a relatively narrow interval of functioning ionomer percentages. These results provide a practical guide for electrode preparation in AAEM-based fuel cell research.

Oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts play an important role in energy conversion and storage devices, but highly active and robust nonprecious metal catalysts are required to address the cost and durability issues. In this work, a modified gel methodology has been used to obtain nanocomposites of perovskite CoTiO 3 and N-doped reduced graphene oxide (NrGO). Moreover, the influence of the annealing extent in the synthesis has been studied. The composites show higher activity in oxygen evolution and reduction reactions in alkaline environment compared to sole ilmenite, which is related to a strong interaction between cobalt titanate and NrGO carbon matrix. The annealing duration appears as a key variable to modulate the physicochemical properties and the electrochemical behavior. The composite prepared at the largest duration (3 hours) exhibit enhanced bifunctional properties for ORR and OER, with onset potentials of 0.93 V and 1.53 V vs. RHE respectively, which is mainly attributed to higher concentration of nitrogen, larger extent of defects and/or the presence of more oxidized Co species in the nanocomposite.

Bifunctional oxygen electrocatalysts are essential in the development of low-temperature unitized regenerative fuel cells (URFCs), as a promising alternative for storing energy via hydrogen. TiO 2 , as a semiconductor material, is commonly not established as an active electrocatalyst for oxygen reduction and oxygen evolution due to its poor electrical conductivity and low reactivity. Here, we demonstrated that composites composed of TiO 2 and N-doped graphene can be active in oxygen reduction and evolution reactions in an alkaline environment. Combination factors such anatase/rutile interaction, N-doping graphene, and the presence of Ti 3+ /Ti–N species raise the active sites and improve the electrochemical activity. Our results may afford an opportunity to develop a non-noble and promising electrocatalyst in energy storage technology.