Self‐Supporting Electrodes for Gas‐Involved Key Energy Reactions

Abstract

Self‐supporting materials are widely adopted in gas‐involved electrocatalysis during the past few decades because of their unique physical/electrochemical properties, especially the stabilized spatial framework and the large electrochemical interfaces. Reportedly, there is no clear definition to define “self‐supporting” materials, and also, no such comprehensive reviews have fully discussed the self‐supporting materials in gas‐involved electrochemical applications. Therefore, it is necessary to provide timely updates in this potential field. In this review, for the first time, a reasonable definition of self‐supporting materials and comprehensively review the recent research progress of related electrodes in gas‐involved electrocatalytic applications is given. Firstly, it is discussed their synthetic methodologies, including design principles, different types of substrates‐ and substrate‐free structures. Subsequently, the recent advances of self‐supporting electrodes for gas‐involved key energy related electrocatalysis (i.e., hydrogen evolution, oxygen reduction, oxygen evolution, nitrogen reduction, and carbon dioxide reduction reactions) and their practical applications in water‐splitting, fuel cells and metal‐air batteries are mainly presented. Finally, a summary of the progress of self‐supporting electrocatalysts, the remaining challenges, and the perspectives are given to instruct their future development. It is expected that this review will provide new research insights for the future development of renewable energy storage and conversion systems.

Pd Doped Co3O4 Loaded on Carbon Nanofibers as Highly Efficient Free-Standing Electrocatalyst for Oxygen Reduction and Oxygen Evolution Reactions

“…For OER, the potential corresponding to current density of 10 mA cm −2 (E j10 ) is 1.48 V, compared with 1.56 V for commercial RuO 2 catalysts. As shown in Figures 4B,E , Pd-Co 3 O 4 @CNF exhibits the lowest Tafel slopes (73.1 mV dec −1 and 65.7 mV dec −1 ) for both OER and ORR, revealing the enhanced reaction kinetics ( Wang et al, 2021 ). The Nyquist plots of catalysts as shown in Figures 3C,F demonstrated that Pd-Co 3 O 4 @CNF oxygen electrode has the lowest charge transfer resistance, indicating that the electrocatalysis process is enhanced .…”

“…Due to the close lattice structure, Pd is considered to have comparable performance with Pt in electrochemical applications ( Cheng et al, 2020 ). Riley synthesized dodecagon N-doped PdCoNi carbon-based nanosheets demonstrating superior performance for electrocatalytic water splitting and suitable for wide pH electrolytes ( Wang et al, 2021 ). Thus, combining Pd with composite substrates could significantly improve the proton transfer rate, reaction kinetics, thereby effectively enhancing the catalytic performance.…”

Developments and Perspectives on Robust Nano‐ and Microstructured Binder‐Free Electrodes for Bifunctional Water Electrolysis and Beyond

“…Hence, significant research effort has been dedicated to the fabrication of different dimensional electrocatalysts with controlled 1D, 2D, and 3D morphologies with regulated size and shape on a variety of conductive substrates, such as tions, the catalysts need to provide continuous gas evolution (i.e., H 2 , O 2 ) at a high current density (≈1 A cm -2 with stability for a few thousands of hours), and the use of these powdery nanocatalysts coated on the current collector (typically glassy carbon; GC) is limited by the complex fabrication process and deterioration in electrocatalytic performance and stability. [55,64,75,76] Meanwhile, an inappropriate optimization/use of binders may lead to an increase of resistance, inhibit mass and charge transport and bury the real active sites, as shown in Figure 1a, to reduce the overall catalytic activity. In addition, the low electrical conductivity of several powder-based nanocatalysts necessitates the use of conductive additives (e.g., carbon black).…”

“…The three-phase main steps during the electrode reaction are shown in Figures 1b and 2; these include i) mass transfer (i.e., transfer of ions/molecules from the bulk electrolyte to the electrocatalytic surface), ii) electron transfer from the substrate to electrocatalysts surface and iii) electrocatalytic surface reaction employing adsorption of ions/molecules, charge transfer, reconstruction of molecules, rupture/creation of chemical bonds, and desorption of reaction intermediates/products at the active sites surface. [76,[82][83][84] For an easier understanding, the effect of powder-based nanocatalysts and nano-and microstructured binder-free electrocatalysts on electrocatalytic activity is compared and discussed from two main perspectives such as electron transfer and mass transfer (Figure 2). As shown in Figures 1 and 2, engineering the dimensionality of nano-and microstructured catalysts on a conductive substrate has been widely employed as an effective strategy to improve catalytic performance.…”

In situ construction of self-supporting Ni–Fe sulfide for high-efficiency oxygen evolution

“…[31][32][33] With regards to the micro-structure influencing the electrocatalytic activity, the design and construction of self-supporting electrodes based on two-dimensional (2D) nanosheets are appealing in optimizing the mass transfer and utility rate of the active sites. [34][35][36][37][38][39] However, it is still challenging to tune the specific parameters of 2D nanosheet-based self-supporting multiple metal sulfide electrodes.…”