Structural Variations of Metal Oxide‐Based Electrocatalysts for Oxygen Evolution Reaction

Abstract

including solar, wind, hydro, and biofuel, are highly desired to reduce our reliance on fossil fuels. However, according to the data provided by International Energy Agency, the global energy demand is 120 Mtoe in 2019, most (80%) of which was derived from fossil fuels (coal, natural gas, oil), leading to a huge CO 2 emission (33Gt in 2019). [1][2][3] One of the difficulties hindering the widespread use of these renewable energy sources is their intermittent and unpredictable nature. [4,5] Electrochemical reaction, a promising strategy for converting intermittent electricity into chemical energy, can produce a wide variety of important fuels and chemical feedstock, including hydrogen, hydrocarbons and ammonia. [6][7][8] The feedstocks for these productions obtained from electrochemical reactions can be offered by abundant and universal source, such as water, carbon dioxide and nitrogen. In last decades, due to the net-zero carbon emission features, electrochemical reactions have initiated extensive investigations based on water splitting reaction, nitrogen reduction reaction (NRR) and carbon dioxide reduction reaction. [9][10][11][12] In these green technologies, electrocatalytic oxygen evolution reaction (OER), a core reaction of these process, has a direct impact on device efficiency and cost effectiveness (Figure 1). [13,14] However, OER involves multistep four-electron transferring steps associated with OH breaking and OO formations, thus suffering from sluggish kinetics and requiring a high energy loss (high potential). Therefore, efficient and stable OER electrocatalysts are required to make these renewable energy storage/conversion processes to be viable and scalable technologies. [15,16,221,222] The OER catalysts can be classified into two categories: [17,18] molecular catalysts for homogeneous system and solid catalysts for heterogeneous system. In the homogeneous catalytic system, the molecular catalysts and the electrolyte are in solution, and the OER takes place in the liquid phase. The performance of molecular OER catalysts can be explained and understood at a molecular level by many relatively simple spectroscopic physicochemical techniques. Based on the mechanistic understanding at a molecular level, their geometric and electronic properties are much easier to be fine-tuned to achieve optimum performance by careful selection of the metal ion and ligand environment. Despite all these advantages, molecular catalysts are still not appropriate to be used in practical Electrocatalytic oxygen evolution reaction (OER), an important electrode reaction in electrocatalytic and photoelectrochemical cells for a carbonfree energy cycle, has attracted considerable attention in the last few years. Metal oxides have been considered as good candidates for electrocatalytic OER because they can be easily synthesized and are relatively stable during the OER process. However, inevitable structural variations still occur to them due to the complex reaction steps and harsh working conditions of OER, thus impending the ...

Synthesis of NiSe2/Fe3O4 Nanotubes with Heteroepitaxy Configuration as a High‐Efficient Oxygen Evolution Electrocatalyst

“…[7,8] Therefore, it is urgent to design lowcost but efficient and stable OER electrocatalysts. To this end, transition metal-based electrocatalysts, such as oxides/hydroxides, [9][10][11][12] selenides, [13][14][15][16] sulfides, [17][18][19] and phosphides, [20,21] scheme for the synthetic approach is illustrated in Figure 1. Briefly, unique PB nanotubes are obtained by a solvothermal method, whose morphology differs from those PB polyhedrons in previous literature.…”

“…[ 7,8 ] Therefore, it is urgent to design low‐cost but efficient and stable OER electrocatalysts. To this end, transition metal‐based electrocatalysts, such as oxides/hydroxides, [ 9–12 ] selenides, [ 13–16 ] sulfides, [ 17–19 ] and phosphides, [ 20,21 ] have been developed in recent years. However, insufficient exposure of active sites on the surface of the bulk electrocatalysts is still intractable, making a relative slow ions transport passing throughout the catalyst and thereby limiting their electrochemical performance.…”

Thein situformation of defective CoOOH catalysts from semi-oxidized Co for alkaline oxygen evolution reaction

“…The formation of CoOOH through oxidation of cobalt ions to higher valence states under OER conditions is crucial since the newly generated CoOOH is considered the active species for the OER. [19][20][21][22][23][24][25] This transformation process from a Co-based precatalyst to CoOOH is strongly related to its initial structure, which might be a key reason for the observed different OER activities of different Cobased compounds. [26][27][28] For instance, based on operando XAS and other electrochemical techniques, it has been disclosed that for spinel Co 3 O 4 , the Co 2+ sites act as active sites that release electrons under applied bias with a close affinity to oxygen to form CoOOH, while the Co 3+ sites are relatively stable and thus limit its catalytic activity.…”

Highly dispersed Ru nanoclusters anchored on B,N co-doped carbon nanotubes for water splitting

“…Searching for suitable electrocatalysts is important to promote the wide application of many new energy conversion processes, including HER, OER, oxygen reduction reactions and so on. 1–5 These important electrocatalytic reactions have to rely on expensive precious metals. In order to reduce the precious metal dosage as much as possible and to improve the utilization efficiency, an effective strategy is to load precious metals onto substrate materials.…”