Multi-Scale Engineered 2D Carbon Polyhedron Array with Enhanced Electrocatalytic Performance

Multiscale Design of Array-Type Integrated Electrodes for Gas-Involving Electrocatalytic Reactions

Oxygen evolution/hydrogen evolution/oxygen reduction reactions (OER/HER/ORR) are core processes of electrochemical energy conversion technologies, which are of great significance to sustainable society. With the common gas-involving characteristic, these electrocatalytic reactions are inevitably faced with sluggish intrinsic kinetics at large current conditions, due to difficult mass transfer in multiphase conversion processes. Accordingly, array-type integrated electrodes are regarded as a promising solution, while relevant design strategies are systematically summarized from multiscale perspectives in this review. On one hand, macroscopic multidimensional structural designs are illustrated considering advantages and limitations of various one/two/three-dimensional (1D, 2D, 3D) array units; on the other hand, microscopic chemical/interfacial structural designs are emphasized by various strategies including ionic regulation, vacancy design, phase conversion, and interface engineering, etc. Furthermore, composite strategies are discussed in terms of surface, hierarchical, phase and atomic levels, especially on how to integrate macroscopic structural and microscopic chemical designs simultaneously. Finally, design rules of array-type integrated electrodes as well as outlooks for mass transfer strategies toward gas-involving reactions are provided.

Nitrogen-Doped Porous Nanofiber Aerogel-Encapsulated Staphylo-Ni3S2 Accelerating Polysulfide Conversion for Efficient Li-S Batteries

The low conductivity of sulfur substances and the fussy effect of lithium polysulfides (LPS) limit the practical application of lithium-sulfur batteries (LSBs). In this work, Ni3S2 is in situ synthesized on N-doped 3D carbon nanofibers with an optimized pore structure as a cathode material for LSBs. The conductive carbon nanofiber skeleton with a hierarchical (micropore-mesopore-macropore) structure etched by Cd2+ can reduce the interface resistance of the cathode and remiss volume expansion during charge-discharge progress. The Ni was vulcanized and nitrogen-doped successively during the annealing process. In addition, the polar Ni3S2 and N-doped carbon structure can promote the catalytic conversion of LPS and regulate the 3D nucleation of Li2S, which could reduce the reaction energy barrier. Therefore, the NCF-Cd-Ni3S2-NC cathode can maintain a high initial capacity (1080.2 mAh g-1) and excellent stability at 0.1C. This work provides an important basis for the synthesis of high efficiency and inexpensive cathode carrier materials for LSBs.

FeNi-LDH Coated With Orange-Peel Carbon Aerogel for Oxygen Evolution Reaction

In this work, the waste orange-peel was used as carbon source, and the orange-peel derived carbon material can be obtained through simple pyrolysis. Then, we designed the structure of orange-peel carbon aerogel grown on iron-nickel layered double hydroxides in situ to achieve the effect of carbon coating (FeNi-LDH/CA). The oxygen evolution reaction catalytic performance of FeNi-LDH/CA is excellent, far exceeding that of commercial RuO2. In 1 M KOH, the overpotential of FeNi-LDH/CA is only 250 mV (10 mA cm-2), obviously better than that of commercial RuO2 (295 mV). FeNi-LDH/CA shows good cycling stability, and after long-term i-t testing, the performance only decays by 3 % after running at 100 mA cm-2 for 100 h. When used as an anode, the voltage of water-splitting is only 1.48 V at 10 mA cm-2. The rechargeable liquid zinc-air battery based on Pt/C-FeNi-LDH/CA catalyst has higher open-circuit voltage (1.543 V) and galvanostatic discharge capacity at 1.23 V (830 min, 10 mA cm-2). Moreover, the zinc-air battery based on Pt/C-FeNi-LDH/CA has a small charge-discharge voltage gap (0.65 V) at 10 mA cm-2, after 200 consecutive cycles (66 h), the charge-discharge voltage gap only increased by about 30 mV, indicating good cycling stability.

2D arrays of hollow carbon nanoboxes: outward contraction-induced hollowing mechanism in Fe-N-C catalysts

Maximizing the utilization efficiency of monatomic Fe sites in Fe-N-C catalysts poses a significant challenge for their commercial applications. Herein, a structural and electronic dual-modulation is achieved on a Fe-N-C catalyst to substantially enhance its catalytic performance. We develop a facile multi-component ice-templating co-assembly (MIC) strategy to construct two-dimensional (2D) arrays of monatomic Fe-anchored hollow carbon nanoboxes (Fe-HCBA) via a novel dual-outward interfacial contraction hollowing mechanism. The pore engineering not only enlarges the physical surface area and pore volume but also doubles the electrochemically active specific surface area. Additionally, the unique 2D carbon array structure reduces interfacial resistance and promotes electron/mass transfer. Consequently, the Fe-HCBA catalysts exhibit superior oxygen reduction performance with a six-fold enhancement in both mass activity (1.84 A cm-2) and turnover frequency (0.048 e- site-1 s-1), compared to microporous Fe-N-C catalysts. Moreover, the incorporation of phosphorus further enhances the total electrocatalytic performance by three times by regulating the electron structure of Fe-N4 sites. Benefitting from these outstanding characteristics, the optimal 2D P/Fe-HCBA catalyst exhibits great applicability in rechargeable liquid- and solid-state zinc-air batteries with peak power densities of 186 and 44.5 mW cm-2, respectively.

Superstructured Carbon with Enhanced Kinetics for Zinc-Air Battery and Self-Powered Overall Water Splitting

The present study proposes a novel engineering concept for the customization of functionality and construction of superstructure to fabricate 2D monolayered N-doped carbon superstructure electrocatalysts decorated with Co single atoms or Co2P nanoparticles derived from 2D bimetallic ZnCo-ZIF superstructure precursors. The hierarchically porous carbon superstructure maximizes the exposure of accessible active sites, enhances electron/mass transport efficiency, and accelerates reaction kinetics simultaneously. Consequently, the Co single atoms embedded N-doped carbon superstructure (Co-NCS) exhibits remarkable catalytic activity toward oxygen reduction reaction, achieving a half-wave potential of 0.886 V versus RHE. Additionally, the Co2P nanoparticles embedded N-doped carbon superstructure (Co2P-NCS) demonstrates high activity for both oxygen evolution reaction and hydrogen evolution reaction, delivering low overpotentials of 292 mV at 10 mA cm-2 and 193 mV at 10 mA cm-2 respectively. Impressively, when employed in an assembled rechargeable Zn-air battery, the as-prepared 2D carbon superstructure electrocatalysts exhibit exceptional performance with a peak power density of 219 mW cm-2 and a minimal charge/discharge voltage gap of only 1.16 V at 100 mA cm-2. Moreover, the cell voltage required to drive an overall water-splitting electrolyzer at a current density of 10 mA cm-2 is merely 1.69 V using these catalysts as electrodes.

Dual-outward contraction-induced construction of 2D hollow carbon superstructures

A novel dual-outward contraction mechanism is applied to construct 2D hollow carbon superstructures (HCSs) via pyrolysis of hybrid ZIF superstructures. One outward contraction stress is offered by the in situ formed thin carbon shell, while another originates from the interconnected facets of ZIF polyhedra within the ZIF superstructure.