Metal-free bifunctional carbon electrocatalysts derived from zeolitic imidazolate frameworks for efficient water splitting,Materials Chemistry Frontiers

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Metal-free bifunctional carbon electrocatalysts derived from zeolitic imidazolate frameworks for efficient water splitting
Materials Chemistry Frontiers ( IF 6.0 ) Pub Date : 2017-11-02 00:00:00 , DOI: 10.1039/c7qm00452d
Yaojie Lei _{1,

2,

3,

4} , Li Wei _{1,

2,

3,

4} , Shengli Zhai _{1,

2,

3,

4,

5} , Yanqing Wang _{6,

7,

8,

9} , H. Enis Karahan _{5,

10,

11} , Xuncai Chen _{1,

2,

3,

4} , Zheng Zhou _{1,

2,

3,

4} , Chaojun Wang _{1,

2,

3,

4} , Xiao Sui _{1,

2,

3,

4} , Yuan Chen _{1,

2,

3,

4}

Affiliation

Metal-free carbon catalysts have attracted great interest because of their high electrical conductivity, tailorable porosity and surface area, affordability, and sustainability. In particular, their bifunctional activity for hydrogen and oxygen evolution reactions (HER and OER) is attractive for electrochemical splitting of water. However, pristine carbon materials have low activities for HER/OER. Here, a high-performance carbon electrocatalyst is demonstrated by first pyrolyzing a metal–organic framework (MOF), i.e., zeolitic imidazolate framework-8 (ZIF-8), followed by optimized cathodic polarization treatment (CPT). Pyrolyzing ZIF-8 produces a highly N-doped (8.4 at%) carbon material having a large specific surface area of 1017 m² g⁻¹ with micro and mesopores. CPT in 0.5 M H₂SO₄ for up to 8 hours modulates the composition of N- and O-containing surface functional groups of the pyrolyzed ZIF-8 without sacrificing its large surface area and pore size distribution. After the 6-hour CPT, this material shows an excellent HER activity in 0.5 M H₂SO₄ electrolyte with an overpotential of 155 mV, a Tafel slope of 54.7 mV dec⁻¹, and an exchange current density of 0.063 mA cm⁻². And the 4-hour CPT results in excellent OER activity in 0.1 M KOH electrolyte with an overpotential of 476 mV and a Tafel slope of 78.5 mV dec⁻¹. In a demonstration, these two carbon electrocatalysts steadily run a two-electrode water electrolyzer at a current density of 10 mA cm⁻² over 8 hours under a potential of 1.82 V with a Faradaic efficiency of 98.0–99.1% in 0.1 M KOH electrolyte. The superior activity of the designed carbon electrocatalysts can be attributed to the functional group composition modulation achieved by CPT. High-performance metal-free carbon electrocatalysts derived from MOFs show excellent potentials for energy and environmental applications.

中文翻译：

源自沸石咪唑酸酯骨架的无金属双功能碳电催化剂，可用于有效的水分解

无金属碳催化剂因其高电导率，可调节的孔隙率和表面积，可负担性和可持续性而引起了人们的极大兴趣。特别是，它们对氢和氧的放出反应（HER和OER）的双功能活性对于水的电化学裂解很有吸引力。但是，原始碳材料对HER / OER的活性较低。在这里，通过首先热解金属有机骨架（MOF），即沸石咪唑酸酯骨架8（ZIF-8），然后进行优化的阴极极化处理（CPT），证明了一种高性能的碳电催化剂。热解ZIF-8产生高N掺杂（8.4 at％）的碳材料，其比表面积大1017 m ² g ^-1微孔和中孔。在0.5 MH ₂ SO _4中进行长达8小时的CPT可以调节热解ZIF-8的含N和O的表面官能团的组成，而无需牺牲其大的表面积和孔径分布。在6小时的CPT之后，该材料在0.5 MH ₂ SO ₄电解质中显示出出色的HER活性，其超电势为155 mV，Tafel斜率为54.7 mV dec ^-1，交换电流密度为0.063 mA cm ^-2。并且4小时的CPT在0.1 M KOH电解液中具有出色的OER活性，过电势为476 mV，Tafel斜率为78.5 mV dec ^-1。在一个演示中，这两种碳催化剂在0.12 KOH电解液中以1.82 V的电势在8小时内以10 mA cm ^-2的电流密度稳定运行了两电极水电解槽，法拉第效率为98.0–99.1％。设计的碳电催化剂的优异活性可以归因于CPT实现的官能团组成调节。源自MOF的高性能无金属碳电催化剂在能源和环境应用方面显示出极好的潜力。

更新日期：2017-11-15

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