3D Holey‐Graphene Architecture Expedites Ion Transport Kinetics to Push the OER Performance

Abstract

The electrochemical oxygen evolution reaction (OER) have been regarded as one of the most important process in a wide range of the above renewable-energy technologies. [6][7][8][9] However, OER is kinetically challenging, and highly desirable for effective electrocatalysts. Ir-and Rubased materials exhibit the highest activity for these electrochemical reactions, but these precious-metal catalysts cannot be largely used for clean energy because of their scarcity on earth and high cost. [10,11] Therefore, nonprecious metal catalysts has attracted considerable attention, [12] for example, nickel (Ni)-based catalyst, which is earth-abundant, low-cost, and environment-friendly. [13,14] There are generally three strategies to improve the activity of an electrocatalyst system: 1) increasing the number of active sites on a given electrode, for example, through increased loading or improved catalyst structure to expose more active sites per gram; [15,16] 2) increasing the intrinsic activity of each active site, for example, through doping with other elements; [17][18][19] 3) increasing the conductivity of catalyst by loading catalyst onto graphene or pure metal. [20,21] However, less attention has been paid on the scrutiny of ion transport behaviors during water splitting process, which limits the OER performance improvement in practice. [22] Herein, via a strategy of facial aqueous-phase chemical etching, we have acquired 3D holey-graphene framework [23] (HGF) as a catalyst-loading platform based on which the OER performance has been further pushed. Analyzing electrochemical measurements, the weakened ion transport domination in the electrochemical reaction is corroborative. On the basis of a series of models ranging from simplified equivalent circuit gradually to practical transmission line, the ion transport resistance related to ion diffusion kinetics is quantified. After investigating the trend in OER performance by increasing etching time, the significance of the balance between the ion transport at the electrode/electrolyte interface and the charge transport inside electrode should be emphasized. Introducing suitable nanoscale pores to enhance the ion transport efficiency for full utilization of the deeply buried active sites, the OER limit could be broken via weakening the electrochemical diffusion domination.The kinetics process of heterogeneous catalysis involves several steps including adsorption, diffusion, and surface chemical reactions. Current studies generally aim at increasing active site amount and improving intrinsic activity. However, the ion diffusion kinetics at the electrode/electrolyte interface as a bottleneck has been rarely directly addressed. Here, a 3D holey-graphene framework is demonstrated as a catalyst-loading platform, with nanoscale holes that can be elaborately tuned via facile aqueous-phase chemical etching. This enables the ions to be efficiently transported to deeply buried active sites to mitigate their insufficient supply. With systematical electrochemical investigations tuned by ...

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