中文题名: | 钴基自支撑纳米阵列催化剂的构筑及其电催化水分解性能研究 |
姓名: | |
保密级别: | 公开 |
论文语种: | 中文 |
学科代码: | 070304 |
学科专业: | |
学生类型: | 博士 |
学位: | 理学博士 |
学位类型: | |
学位年度: | 2023 |
校区: | |
学院: | |
研究方向: | 电催化水分解 |
第一导师姓名: | |
第一导师单位: | |
提交日期: | 2023-01-05 |
答辩日期: | 2022-12-17 |
外文题名: | CONSTRUCTION OF SELF-SUPPORTED COBALT-BASED NANOARRAY CATALYSTS AND THEIR ELECTROCATALYTIC PERFORMANCES FOR WATER SPLITTING |
中文关键词: | |
外文关键词: | Cobalt-based low dimensional nanoarrays ; Self-supported electrocatalysts ; Water electrolysis ; Electrochemical reconstruction ; Structure-activity relationship ; HER and OER reaction mechanism |
中文摘要: |
人类社会对不可再生化石燃料的大规模使用不可避免地造成能源短缺和环境污染,因而寻找和发展新型可再生清洁能源来替代传统化石能源显得尤为重要。在各种清洁能源中,氢气因其高的能量密度、可再生以及零碳排放等优点被认为是一种极有应用前景的能源载体。理论上,电解水制氢是实现可持续、环境友好、大规模生产氢气最可行方法之一。然而,阴极析氢反应(HER)和阳极析氧反应(OER)常需采用昂贵的Pt基和Ru/Ir基材料作为催化剂来克服析氢和析氧高过电位以及动力学缓慢的桎梏,从而大幅提升了电解水的成本,限制了电解水产氢的实际应用。显然,开发低成本、高效、耐用的非贵金属基催化剂是实现电解水产氢大规模应用的关键。在众多的非贵金属催化材料中,钴基化合物(如钴基氧化物/氢氧化物、钴基硫属化合物、钴基磷化物等)对HER和OER均表现出优异的电催化性能,因而引起了广泛的关注。遗憾的是,目前钴基材料仍然存在导电性差、本征活性低、稳定性不高、真实活性物质的活性起源认识不清、催化活性位点识别困难等局限。本论文致力于解决上述难题,以构筑在导电基底上的钴基纳米阵列为研究对象,通过阴离子掺杂/置换工程调控了其形貌、组成乃至电子结构,实现了对其HER或OER 性能的调控;并系统研究了含不同阴离子的钴基纳米阵列在OER中的自重构行为,加深了对催化剂电化学重构以及OER真实活性物质的认识。特别是,利用离位/原位测试手段探究了催化剂的活性物质和活性位点,并借助理论计算深入探究了HER 和 OER催化机理,从原子水平揭示了催化剂活性位点及其构-效关系,为高效HER和OER催化剂的设计开发提供了新思路。本学位论文的具体研究内容与研究成果如下: 1. 利用简单的水热反应结合气相后掺杂策略在碳纤维纸(CFP)上制备出P掺杂的NiCo2Se4中空纳米针阵列(即P-NiCo2Se4/CFP)。发现最优阵列(P8.71-NiCo2Se4/CFP)在全pH范围内均表现出优异的电催化HER性能:在酸性、碱性和中性介质中达到10 mA cm?2电流密度时的过电位分别低至33、57和69 mV,相应的Tafel斜率分别为52、61和72 mV dec?1;其性能优于众多先进的非贵金属HER催化剂,尤其是在中性和碱性介质中大电流密度下的催化性能甚至优于商用Pt/C催化剂。特别是,P8.71-NiCo2Se4/CFP在强腐蚀性的酸性和碱性电解质中也表现出良好的耐久性。实验和理论研究进一步揭示,P原子掺杂NiCo2Se4可调节各活性位点的局部电子态,使Ni的d带中心和Se的p带中心上移并引入P活性位点,进而同时优化了其H*吸附/脱附能、水吸附能和水解离能,加速HER在不同pH介质中的决速步骤,从而使P-NiCo2Se4在全pH范围内均具有优异的电催化HER性能。本项研究对催化剂在不同电解环境中活性位点的催化作用提供了原子水平的见解,从而为高效pH通用型非贵金属基HER催化剂的设计提供了新的思路。 2. 开发了一种水热反应结合电化学阴离子掺杂合成新策略,首次在导电CFP上生长出非晶多孔NiCo2(S1-xSex)4中空纳米棒阵列(即a-NiCo2(S1-xSex)4/CFP)。值得注意的是,优化a-NiCo2(S0.84Se0.16)4/CFP阵列对碱性HER和OER均表现出极高的电催化活性和优异的稳定性:其在100 mA cm?2电流密度下的过电位分别仅为98和215 mV;当将其应用于全解水时,只需超低的槽压(1.578 V)即可获得100 mA cm?2电流密度且电解性能在200小时内基本无衰减;特别是在1.5 V干电池或微型太阳能电池板驱动下也能实现高效水分解;其在大电流密度下的全解水性能优于绝大多数已报道的非贵金属基催化剂。实验和理论研究进一步揭示,a-NiCo2(S1-xSex)4/CFP优异的HER性能不仅源于其独特纳米结构所带来的丰富活性位点和有利的物质与电荷传递通路,还得益于Se掺杂所引起Co和Ni位点上水解离能的降低以及Ni位点上H*吸附/脱附能的优化。而在探究其OER性能时,发现a-NiCo2(S1-xSex)4在进行循环伏安法(CV)活化后易发生完全重构,转变为Se, S共掺杂Ni0.33Co0.67OOH纳米片分级结构(即Se, S-Ni0.33Co0.67OOH);并揭示Se原子掺杂到S-Ni0.33Co0.67OOH中能调节Co活性中心的局域电子态,使其d带中心下移以平衡对含氧中间体吸附强度,进而优化四个串联基元步骤的能量并降低决速步骤能垒,从而获得优异的OER性能。本项研究为从原子水平理解HER和OER催化剂的构-效关系以及为设计高效全解水双功能催化剂提供了新的见解。 3. 采用水热反应结合管式炉气相法合成出一系列生长在CFP上的Co基纳米针阵列(即CoxAy (A = P, S, Se)/CFP)。当将这三种阵列在1 M KOH溶液中进行恒电流活化(10 mA cm?2,1 h)后,发现它们均发生明显的组成和结构重构,形成以纳米针为骨架、纳米片为次级结构的CoOOH分级结构(分别标记为CoP-CR-CoOOH、CoS2-CR-CoOOH和CoSe2-CR-CoOOH)。进一步研究揭示,上述三种阵列所重构出的纳米片单元都含有大量的活性位点和丰富的氧空位,其中以CoSe2-CR-CoOOH阵列尤为突出。当在1 M KOH溶液中进行电化学测试时,CoSe2-CR-CoOOH阵列显示出最优的OER性能:仅需要280 mV的低过电位就可达到10 mA cm?2电流密度,对应的塔菲尔斜率仅为52 mV dec?1,性能优于大多数非贵金属基催化剂。当在强碱性溶液中进行50 h稳定性测试后,三种重构后催化剂的电催化性能均没有明显衰减。综合分析表明,超高的电化学活性表面积、丰富的氧空位以及优化的电子结构相互协同,为CoSe2-CR-CoOOH提供了更多的催化活性中心、增强的导电性以及合适的d带中心(以平衡对含氧中间体吸附强度),进而赋予其优异的OER性能。本研究加深了对含不同阴离子的预催化剂电化学重构行为和OER真正活性物质的活性起源认识,为设计高性能的非贵金属基OER催化剂提供了新的思路。 |
外文摘要: |
As is well-known, the large-scale consumption of non-renewable fossil fuels has caused severe energy shortage and environmental pollution acorss the world. To solve such isssues, it is imperative to develop new renewable clean energies for replacing the traditional fossil energies. Among various clean energies, hydrogen is considered as a promising energy carrier for the future due to its high energy density, renewable and zero carbon emission. Theoretically, electrolysis of water to produce hydrogen is one of the most feasible ways to achieve sustainable, environmentally friendly and large-scale hydrogen production. However, the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) typically require the use of expensive Pt-based and Ru/Ir-based catalysts to overcom the high overpotential and slow reaction kinetics assoicated with HER and OER, thereby greatly increasing the cost of water electrolysis and limiting its practical application. Apparently, the development of low-cost, efficient and durable non-noble metal based catalysts is the key to achieve the large-scale hydrogen production via water electrolysis. Among many non-noble metal catalytic materials, cobalt-based compounds (such as cobalt-based oxides/hydroxides, cobalt-based chalcogenides, cobalt-based phosphides, etc.) have shown excellent electrocatalytic performances for HER and OER, thus attracting wide attention. Unfortunately, cobalt-based materials have still suffered from some limitations, such as poor electrical conductivity, low intrinsic activity, low stability, unclear understanding of the active origin of real active species and difficulty in identifying active sites. To solve such issues, in this thesis, we have specially constructed self-supported cobalt-based nanoarrays on conductive substrates, and employed anion doping/exchang engineering to tune their morphologies, compositions and electronic structures so as to finally improve their HER or OER performances. Moreover, the self-reconstruction behaviors of the cobalt-based nanoarrays containing different anions in OER process have been also systematically studied, thus deepening the understanding of the electrochemical reconstructions of catalysts and the real active species during OER. In particular, the active species and active sites of the catalyst were investigated by ex situ/in situ testing methods, and the catalytic mechanisms of HER and OER were deeply explored by theoretical calculation. Ultimately, the active sites of the catalyst and their structure-activity relationship were revealed at the atomic level, thereby providing some new insights for the design and development of efficient HER and OER catalysts. The main results of this thesis are list as following: 1. A simple hydrothermal route combined with a post gas-phase doping strategy was developed to fabricate P-doped NiCo2Se4 hollow nanoneedle arrays on carbon fiber paper (i.e., P-NiCo2Se4/CFP). Notably, the optimal arrays (P8.71-NiCo2Se4/CFP) could afford an outstanding pH-universal HER performance, with an overpotential as low as 33, 57, and 69 mV at 10 mA cm?2 current density and a corresponding Tafel slope of 52, 61, and 72 mV dec?1 in acidic, alkaline, and neutral media, respectively, outperforming most state-of-the-art nonprecious HER catalysts and even the commercial Pt/C catalyst in both neutral and alkaline media at large current densities. Impressively, P8.71-NiCo2Se4/CFP also displayed good durability toward long-time stability testing in harsh acidic and alkaline electrolytes. Experimental and theoretical studies further revealed that the doping of P atoms into NiCo2Se4 could simultaneously optimize its H* adsorption/desorption energy, water adsorption energy, and water dissociation energy by adjusting the local electronic states of various active sites to cause the upshift of the d-band center of Ni and the p-band center of Se and the introduction of the P active site, thus accelerating the rate-determining step of HER in different pH media to endow P-NiCo2Se4 with an outstanding pH-universal HER performance. This study provides atomic-level insights into the roles of active sites of catalysts in various electrolysis environments, thereby shedding new light on the rational design of highly efficient pH-universal nonprecious catalysts for HER. 2. A hydrothermal reaction combined with electrochemical anion doping strategy was firstly developed to construct amorphous porous NiCo2(S1-xSex)4 hollow nanorod arrays grown on conducting CFP (i.e., a-NiCo2(S1-xSex)4/CFP). Notably, the optimal a-NiCo2(S0.84Se0.16)4/CFP arrays exhibited an extremely high electrocatalytic activity and excellent stability for both alkaline HER and OER, requiring an overpotential of only 98 and 215 mV respectively to deliver a current density of 100 mA cm?2. When it is applied to the overall water splitting, it only required a cell voltage as low as 1.578 V to obtain 100 mA cm?2 current density and showed a negligible performance degradation after 200 h electrolysis. Noteworthily, such a water electrolyzer could also be efficiently driven by a 1.5 V commercial dry battery or a miniature solar panel. In comparsion, its overall water splitting performance at high current density is better than that of most non-precious metal based catalysts. Experimental and theoretical studies further revealed that the excellent HER catalytic performance of a-NiCo2(S1-xSex)4/CFP was attributed to not only the abundant active sites and the favorable mass and charge transfer pathways brought by its unique nanostructure, but also the reduction of water dissociation energy at Co and Ni sites and the optimization of H* adsorption/desorption energy at Ni sites caused by Se doping. As far as their OER performances were concerned, a-NiCo2(S1-xSex)4 were found to easily undergo complete reconstruction after cyclic voltammetry (CV) activation and to finally transform into Se, S-codoped Ni0.33Co0.67OOH hierarchical nanoarchitectures (i.e., Se, S-Ni0.33Co0.67OOH). The combined experimental and theoretical studies revealed that the doping Se into S-Ni0.33Co0.67OOH could optimize four step energy and reduce the energy barrier for the rate-determining step by tuning the local electronic states of Co active sites to cause the downshift of their d-band centers for balancing the adsorption strength to oxygen containing intermediates, thus allowing S, Se-Ni0.33Co0.67OOH to have an outstanding OER performance. This study provides new insights for understanding the structure-activity relationship between HER and OER catalysts at the atomic level and for designing highly efficient bifunctional catalysts for water splitting.
3. A series of uniform
Co-based nanoneedle arrays with different compositions grown on CFP (i.e., CoxAy (A = P, S, Se)/CFP) were controlled fabricated via a hydrothermal route
combined with a subsequent gas phase conversion process. Upon activation in 1 M
KOH solution at a constant current (10 mA cm?2) for 1 h, the three
nanoarrayes were found to undergo obvious composition and structural
reconstruction, forming CoOOH hierarchical nanostructures (labeled as
CoP-CR-CoOOH, CoS2-CR-CoOOH and CoSe2-CR-CoOOH,
respectively) with the nanoneedles as the skeletons and the newly formed
nanosheets as the secondary structures. Closer inspections unveiled that the
as-formed CoOOH hierarchical structures all contained abundant active sites and
rich oxygen vacancies, among which CoSe2-CR-CoOOH posesssed the most
active sites and the highest oxygen vacancy content. Upon testing in 1 M KOH
solution, the CoSe2-CR-CoOOH array showed the optimal OER
performance: exhibited a Tafel slope of 52 mV dec?1 and an
overpotential of 280 mV at 10 mA cm?2, superior to that of most non-precious
metal based catalysts. Notably, the electrocatalytic performance of the three
reconstructed nanoarrys did not decline significantly after 50 h stability test
in strong alkaline solution. Further comprehensive analysis showed that it was the
ultrahigh electrochemical active surface area, rich oxygen vacancies and
optimized electronic structures that worked together to allow CoSe2-CR-CoOOH
with abundant catalytic active centers, enhanced conductivity and appropriate
d-band centers (to balance the adsorption strength to oxygen-containing
intermediates) so as to achieve excellent OER performance. This study deepens
the understanding of the electrochemical reconstruction behavior of the
precatalysts containing different anions and the active origin of the real
active species in OER, thus sheding new light on the development of high
performance non-noble metal based OER catalysts.
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参考文献总数: | 395 |
馆藏地: | 图书馆学位论文阅览区(主馆南区三层BC区) |
开放日期: | 2024-01-05 |