Tremendous efforts have been dedicated into the development of high‐performance energy storage devices with nanoscale design and hybrid approaches. The boundary between the electrochemical capacitors and batteries becomes less distinctive. The same material may display capacitive or battery‐like behavior depending on the electrode design and the charge storage guest ions. Therefore, the underlying mechanisms and the electrochemical processes occurring upon charge storage may be confusing for researchers who are new to the field as well as some of the chemists and material scientists already in the field. This review provides fundamentals of the similarities and differences between electrochemical capacitors and batteries from kinetic and material point of view. Basic techniques and analysis methods to distinguish the capacitive and battery‐like behavior are discussed. Furthermore, guidelines for material selection, the state‐of‐the‐art materials, and the electrode design rules to advanced electrode are proposed.

wileyonlinelibrary.comdiffi culty of uniformly dispersing both CNTs and graphene in polymer matrices and the high-performance demands of electrical conductivity without severe deterioration during stretching. First, because of the high aspect ratio and strong π-π interactions among carbon nano-materials, CNTs tend to bundle and aggregate, and graphene sheets are easy to stack in the matrices. [11][12][13] These processes would all have an adverse impact on the electrical performance of the SCMs. Second, partial breaks and cracks in the conductive networks of matrices are familiar occurrences when the SCMs are stretched to an extremely large strain, for example, 50%. [ 14 ] Therefore, the stretching range will be limited to maintain the excellent electrical performance of SCMs for practical applications.A large number of studies are targeted to addressing these limitations. [15][16][17][18] One attractive and effi cient method to improve the distribution and dispersion of these carbon nano-materials in SCMs is to construct their three-dimensional (3D) structures in advance and then impregnate them within the polymer. [ 23 ] Nevertheless, the commonly used 3D network preparation methods (e.g., organic sol-gel polymerization, [19][20][21] chemical and hydrothermal reduction, [ 22,23 ] and chemical vapor deposition [ 24,25 ] are complex, expensive and time consuming. Therefore, although these structures impart the SCMs with high electrical conductivity while maintaining a low nanofi ller loading, the large-scale manufacturing of CNTs and/or graphene 3D networks is still largely restricted. Moreover, the electrical conductivities of these 3D carbon nano-material-based polymer composites generally exhibit gradual decreases with increasing strains, [ 16,17 ] thereby resulting in signifi cantly reduced conductivities under large strains. For example, in our previous work, the conductivity of a CNT/graphene aerogel/poly(dimethylsiloxane) (PDMS) fi lm exhibited a ≈30% decrease under 30% strain, [ 16 ] and a graphene foam/PDMS composite also revealed a 30% decrease under 50% strain. [ 13 ] This phenomenon is due to cracking of the conductive network under stretching, which would be more prominent under large deformations. Regarding this point, J. Park et al. provided a new design opportunity for obtaining high electrical conductivity performance from SCMs under large strains from the perspective of the polymer substrate. [ 18 ] Their specially designed porous PDMS exhibited a signifi cantly Here, a novel and facile method is reported for manufacturing a new stretchable conductive material that integrates a hybrid three dimensional (3D) carbon nanotube (CNT)/reduced graphene oxide (rGO) network with a porous poly(dimethylsiloxane) (p-PDMS) elastomer (pPCG). This reciprocal architecture not only alleviates the aggregation of carbon nanofi llers but also signifi cantly improves the conductivity of pPCG under large strains. Consequently, the pPCG exhibits high electrical conductivity with a low nanofi ller loading (27 S m −1 wi...

Developing low-cost and efficient electrocatalysts to accelerate oxygen evolution reaction (OER) kinetics is vital for water and carbon-dioxide electrolyzers. The fastest-known water oxidation catalyst, Ni(Fe)O x H y , usually produced through an electrochemical reconstruction of precatalysts under alkaline condition, has received substantial attention. However, the reconstruction in the reported catalysts usually leads to a limited active layer and poorly controlled Feactivated sites. Here, we demonstrate a new electrochemistry-driven Fenabled surface-reconstruction strategy for converting the ultrathin NiFeO x F y nanosheets into an Fe-enriched Ni(Fe)O x H y phase. The activated electrocatalyst shows a low OER overpotential of 218 ± 5 mV at 10 mA cm −2 and a low Tafel slope of 31 ± 4 mV dec −1 , which is among the best for NiFe-based OER electrocatalysts. Such superior performance is caused by the effective formation of the Fe-enriched Ni(Fe)O x H y active-phase that is identified by operando Raman spectroscopy and the substantially improved surface wettability and gas-bubble-releasing behavior.

The low hydrogen adsorption free energy and strong acid/alkaline resistance of layered MoS2 render it an excellent pH‐universal electrocatalyst for hydrogen evolution reaction (HER). However, the catalytic activity is dominantly suppressed by its limited active‐edge‐site density. Herein, a new strategy is reported for making a class of strongly coupled MoS2 nanosheet–carbon macroporous hybrid catalysts with engineered unsaturated sulfur edges for boosting HER catalysis by controlling the precursor decomposition and subsequent sodiation/desodiation. Both surface chemical state analysis and first‐principles calculations verify that the resultant catalysts exhibit a desirable valence‐electron state with high exposure of unsaturated sulfur edges and an optimized hydrogen adsorption free energy, significantly improving the intrinsic HER catalytic activity. Such an electrocatalyst exhibits superior and stable catalytic activity toward HER with small overpotentials of 136 mV in 0.5 m H2SO4 and 155 mV in 1 m KOH at 10 mA cm−2, which is the best report for MoS2–C hybrid electrocatalysts to date. This work paves a new avenue to improve the intrinsic catalytic activity of 2D materials for hydrogen generation.

We report the strong catalyst–support interaction in WC‐supported RuO2 nanoparticles (RuO2‐WC NPs) anchored on carbon nanosheets with low loading of Ru (4.11 wt.%), which significantly promotes the oxygen evolution reaction activity with a η10 of 347 mV and a mass activity of 1430 A gRu−1, eight‐fold higher than that of commercial RuO2 (176 A gRu−1). Theoretical calculations demonstrate that the strong catalyst–support interaction between RuO2 and the WC support could optimize the surrounding electronic structure of Ru sites to reduce the reaction barrier. Considering the likewise excellent catalytic ability for hydrogen production, an acidic overall water splitting (OWS) electrolyzer with a good stability constructed by bifunctional RuO2‐WC NPs only requires a cell voltage of 1.66 V to afford 10 mA cm−2. The unique 0D/2D nanoarchitectures rationally combining a WC support with precious metal oxides provides a promising strategy to tradeoff the high catalytic activity and low cost for acidic OWS applications.