Rational Construction of Low-Dimensional Transition Metal Based Material for Energy Storage and Conversion

基於低維過渡金屬的能源存儲及轉化材料的合理構築

Student thesis: Doctoral Thesis

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Award date10 Sep 2020

Abstract

To alleviate severe environmental problems caused by the dramatic usage of fossil fuels and satisfy the demand for higher efficiency, considerable efforts have been made in the field of sustainable energy storage and conversion (ESC) technologies to power our future society. Energy storage devices (e.g., lithium ion batteries (LIBs) and sodium ion batteries (SIBs)) and energy conversion technologies (e.g., water splitting and CO2 reduction reaction), which are an indispensable part in our life, have extensive applications. However, despite their substantial development progress, the practical capacity, rate capability, and cycling stability of batteries, as well as the high-cost, low selectivity, large over potential, poor stability and low yield of electrocatalysts, are limiting their large-scale applications. To advance their practical applications, the exploration of suitable electrode materials and electrocatalysts with inexpensive, superior performance and excellent stability are pivotal step. Recently, low-dimensional (LD) materials have caused increasing concern owing to their distinctive physico-chemical properties, including high aspect ratio, large surface area, ample approachable reactive sites, excellent buffer ability, and satisfactory toughness. Two LD transition metal-based electrodes for energy storage and two LD transition metal-based electrocatalysts for energy conversion are reported in this thesis. Moreover, when evaluated in real battery and electrocatalytic conditions, these electrode materials and catalysts showed superior ESC performance.

For energy storage, we first developed ultrathin dual-phase P-doped Bi2MoO6 nanosheets for LIBs and SIBs via a one-step wet-chemical synthesis approach. Distinct from conventional two-dimensional nanosheets, our newly developed ultrathin P-doped Bi2MoO6 nanosheets exhibit a unique tunable amorphous/nanocrystalline dual-phase structure with the advantages of fast ion exchange ability and superb volume change buffer capability. The presented ultrathin P doped Bi2MoO6 nanosheets reveal a noteworthy high-rate property and ultralong cycling performance, which demonstrates vast potential for use as an anode material for next-generation lithium and sodium storage.

Further, to investigate the effects of dopants in the energy storage system, the N, S co-doped Fe3O4/C nanotubes with ultrathin nanosheets assembled via annealing of the methyl orange-embedded Fe-glycerate were designed and prepared. The nanosheets, which constitute the wall of a nanotube, are formed by small Fe3O4 nanoparticles encased with highly graphitic carbon at a minimum graphitization temperature of 450 °C. The density functional theory (DFT) results verified that the homogeneous N and S dopants can efficiently promote the adsorption of Li+ ions, resulting in accelerated intercalation/deintercalation rate of Li+ ions. Besides, the abundant micro/meso-pores and hieratical nanosheet organized nanotube structure that greatly buffer volume expansion during cycling, as well as the satisfactory conductivity due to the graphitic carbon coating, is also contribute to the outstanding electrochemical performance.

For the energy conversion device, the porous Fe-doped heterostructured Mo-based nanosheets (FeMoP-500) for the hydrogen evolution reaction (HER) was prepared via low-temperature phosphorization of the self-assembled inorganic-inorganic coordinated iron-phosphomolybdic acid metallogel nanosheets (FePMoG). The FeMoP-500 with a polarization potential of 146.3 mV at 200 mA cm-2 and excellent stability over 380 h is one of the best Mo-based HER electrocatalysts. The experiments demonstrate that the plentiful interfaces in the heterostructure and Fe dopants could facilitate the HER activity, while the porous two-dimensional network could increase the active sites density in FeMoP-500. This study provides a new venue for fabricating heterostructured two-dimensional nanosheets with rich phase boundary and enhanced accessible catalytic sites for energy-related applications.

Designing and preparing single metal atom catalyst is another structural engineering tactic for exposing the increased the active sites density in electrocatalysts. Inspired by the project of N, S co-doped Fe3O4/C nanotubes, we discovered that the iron glycerate has a satisfactory catalytic ability to promote the growth of carbon. After a thorough investigation on the formation mechanism, we synthesize an iron/bismuth dual-site single-atom dispersion carbon nanobelt (FeBi-SAs/CNB). This facile FeBi-SAs/CNB with extraordinary electrocatalytic activity far exceeds its counterpart Fe-SAs/CNT.

In general, the facile strategies of manipulating low dimensional (LD) materials reported in this thesis could serve as a guide for designing superior electrode materials and electrocatalysts in ESC. Future studies will focus on the intrinsic mechanism for developing new materials.