Rational design of bifunctional, high-performance, and stable non-noble metal-based electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of great importance and challenging for the realization of overall water splitting. Metal–organic frameworks (MOFs) have been intensively studied as pyrolyzing precursors to prepare electrocatalysts. However, the aggregation of powder and the low conductivity of polymer binders have limited the applications of powder electrocatalysts. Therefore, the direct growth of MOFs on conductive and porous substrates will be a favorable way to prepare efficient electrocatalysts for electrocatalytic water splitting. Herein, we report a facile strategy for constructing three-dimensional N-doped carbon nanotube frameworks derived from metal–organic framework on Ni foam as a bifunctional electrocatalyst for overall water splitting. The resulting electrocatalyst exhibits excellent stability and high OER and HER activity with rather low overpotentials of 230 and 141 mV at 10 mA/cm2 in 1.0 M KOH, respectively. Specifically, the as-synthesized electrodes were used as both the cathode and anode for overall water splitting with 10 mA/cm2 at a cell voltage of only 1.62 V. The outstanding electrocatalytic performance is mainly attributed to a large number of accessible active sites of Co nanoparticles dispersed by the N-doped carbon nanotubes (CNTs) and the ultra-high surface area of CNT frameworks. The presented strategy offers a novel approach for developing MOF-derived nanocarbon materials on Ni foam for electrocatalysis and electrochemical energy devices.

Activated porous carbons (APCs) are traditionally produced by heat treatment and KOH activation, where the production time can be as long as 2 h, and the produced activated porous carbons suffer from relatively low specific surface area and porosity. In this study, the fast high‐temperature shock (HTS) carbonization and HTS‐KOH activation method to synthesize activated porous carbons with high specific surface area of ≈843 m2 g‐1, is proposed. During the HTS process, the instant Joule heating (at a heating speed of ≈1100 K s‐1) with high temperature and rapid quenching can effectively produce abundant pores with homogeneous size‐distribution due to the instant melt of KOH into small droplets, which facilitates the interaction between carbon and KOH to form controllable, dense, and small pores. The as‐prepared HTS‐APC‐based supercapacitors deliver a high energy density of 25 Wh kg‐1 at a power density of 582 W kg‐1 in the EMIMBF4 ionic liquid. It is believed that the proposed HTS technique has created a new pathway for manufacturing activated porous carbons with largely enhanced energy density of supercapacitors, which can inspire the development of energy storage materials.

Global energy crisis and environment pollution have raised ever-growing demand for high-performance energy-storage devices. Supercapacitors (SCs) with fast recharge capability, high power density, and long cycling stability are considered one type of the most promising nextgeneration energy-storage devices. [1,2] Activated porous carbon (APC) with outstanding electrical conductivity, porous structure, and large surface area is the primary electrode materials for SCs. [3] However, the low-energy density of SCs limits their practical application. [4][5][6][7] Generally, APC is prepared by combined carbonization-activation strategies under acidic, alkaline, CO 2 /steam, or other environment at high temperature for a long time. [8,9] To improve the performance of APCbased SCs, a series of strategies have been proposed, such as optimizing the size and distribution pores, [10,11] and impurity doping (N, O, B, S, P) to tune the internal and surface charge properties. [12][13][14][15][16][17][18][19][20][21] These strategies can significantly improve the performance of APC-based SCs under the conditions of long processing time, high temperature, and complex preparation process. These critical conditions can adversely affect the structure of APCs, such as the loss of N and O, which limits the further improvement of the electrochemical performance. Therefore, there is an urgent need for efficient, stable, and safe strategies that can simultaneously optimize the structure of APCs, enlarge the specific surface area, while retain the loss of doping elements.Herein, we propose a strategy to transfer general-purpose carbon into high-energy density SCs carbon with ultrafine structure including high specific surface area and N, O functional groups, within ultrashort time of ≈13 s. [22][23][24][25][26] Typically, APC manufactured by long-term and high-temperature heat treatment of raw carbon (RC) in a tubular furnace (TF) with small amount of N, O element and uneven pores, which has small specific surface area (Figure 1a). By rapid joule heating and subsequent ultrafast cooling (high-temperature shock, HTS), general-purpose carbon can be processed into ultrafine structure with enormous N, O functional groups Supercapacitor (SC) is one of the most promising electrochemical energy-storage devices. However, the practical application of SCs is limited by the low-energy density. Herein, high-temperature shock (HTS)-derived ultrafine structure-activated porous carbon (UAPC) with N, O functional groups is reported as highenergy density SCs carbon. The process of ultrafast joule heating and cooling effectively transfers general-purposed carbon into electrochemical-activated carbon. The UAPC-based SCs exhibit an energy density of up to 129 Wh kg −1 in EMIMBF 4 ionic liquid, which outperform almost all reported and commercial SCs (22 Wh kg −1 ). The outstanding electrochemical performance of UAPC is attributed to the ultrafine structure and N, O functional groups, which enlarges the surface area, improves the surface wettability of UAPC ele...

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Electrocatalytic water splitting to produce hydrogen and oxygen is regarded as one of the most promising methods to generate clean and sustainable energy for replacing fossil fuels. However, the design and development of an efficient bifunctional catalyst for simultaneous generation of hydrogen and oxygen remains extremely challenging yet is critical for the practical implementation of water electrolysis. Here, we report a facile method to fabricate novel N-doped carbon nanotube frameworks (NCNTFs) by the pyrolysis of a bimetallic metal organic framework (MIL-88-Fe/Co). The resultant electrocatalyst, Co 3 Fe 7 @NCNTFs, exhibits excellent oxygen evolution reaction (OER) activity, achieving 10 mA/cm 2 at a low overpotential of just 264 mV in 1 M KOH solution, and 197 mV for the hydrogen evolution reaction. The high electrocatalytic activity arises from the synergistic effect between the chemistry of the Co 3 Fe 7 and the NCNTs coupled to the novel framework structure. The remarkable electrocatalytic performance of our bifunctional electrocatalyst provides a promising pathway to highperformance overall water splitting and electrochemical energy devices.[a] Q.