【作者】 张晗；

【导师】 都兴红； 冯忠宝；

【作者基本信息】 东北大学 ， 冶金工程（专业学位）， 2021， 硕士

【摘要】 氢能作为解决人类能源问题的最具潜力解,近些年来一直被广泛研究,在氢能的制备工艺中,电解水制氢设备简单,原料丰富,只需要一定量的电能就可以实现持续产氢,产出的氢气纯度较高,可直接用于工业生产中。电解水制备氢气过程由阳极上发生的析氧反应(Oxygen evolution reaction)和阴极上发生的析氢反应(Hydrogen evolution reaction)组成,其中,析氧反应中的氧化是一个四电子转移过程,需要消耗大量电能,是限制电解水制氢推广应用的原因,而利用易氧化的替代物的氧化过程去代替析氧反应过程,是一种具有前景的策略,其中,肼的氧化(Hydrazine oxidation reaction)因反应动力学快,能量密度高独居优势,此外,制备出具有大比表面积和快速的物质传输速度的电催化剂则是加速电解过程的关键。研究表明,镍锌合金对析氢反应和肼氧化都展现出一定的催化能力,但由于制备方法复杂且催化性能并没有竞争力,目前镍锌合金被作为双功能催化剂同时催化阳极和阴极两个反应进行产氢还未被深入研究。所以,本文先利用一步气泡模板法制备镍锌合金催化剂并作为电极催化析氢反应和肼氧化反应,研究其电化学性能,其中镍锌合金催化剂催化析氢反应(HER)时只需要68 mV的过电位去实现10 mA cm-2的电流密度,塔菲尔(Tafel)斜率的数值仅为49.3 mV dec-1,在进行肼氧化(HzOR)催化时,0.4 V的电位下能产生620 mA cm-2的大电流密度,Tafel斜率也仅为极小的44.5 mV dec-1,而当该电极同时催化阳极和阴极两个反应时,电流密度达到10、100和200 mA cm-2等不同数值时,其电池电压仅为极小的0.167 V、0.497 V和0.789 V。随后,为了进一步增强催化性能,本文制备得到了镍锌合金还原石墨烯(Ni-Zn/rGO)复合催化剂,结果表明,该催化剂相比于镍锌合金,催化能力得到了进一步提升,并且在最佳NiZn比下,析氢反应(HER)产生10 mAcm-2的电流密度时过电位为很小的49 mV,对应的Tafel斜率也为极小的26.3 mV dec-1,在肼氧化(HzOR)的测试中,Ni-15 at.%Zn/rGO在0.4 V时可产生744 mA cm-2的电流密度,Tafel斜率为33.5 mV dec-1,同时,通过对经过长时间循环后的电催化进行表征和电化学测试,发现其表面形貌得到较完好的保存,这也是电催化活性保持不变的原因,随后进行了粘附力测试,证明了电催化剂表面具有极小的气泡粘附力,这有利于产物气体的顺利脱出,是能持续催化的关键。更多还原

【Abstract】 Hydrogen,as the most potential candidate for clean energy in the furture,has been extensively studied in recent years.Among the preparation methods of hydrogen,electrocatalytic water splitting is regarded as one of ideal approaches due to its simple equipments and abundant raw materials.Only a certain amount of electric energy was required to achieve continuous production.Meanwhile,the prepared hydrogen is high purity and can be directly used in industrial production.Electrocatalytic water splitting consists of the oxygen evolution reaction(OER)at anode and the hydrogen evolution reaction(HER)at the cathode.The oxygen evolution reaction is diseconomy and environmental-unfriendly ascribed to its energy consumption four-electron transfer process,therefore the application of hydrogen production by water splitting is highly restricted.Therefore,replacing OER with some active anodic reactions such as ethanol,glycerol,hydrazine hydrate and ammonia is an effective approach to lower the overpotential of water splitting.Among the above species,hydrazine hydrate is the most promising candidate due to its rapid oxidation kinetics and high power density.Meanwhile,the employment of electrocatalysts with large surface area and fast mass transter play a vital role to lower the HER and HzOR overpotentials.Present studies have proved that good electrocatalytic activity can be observed for Ni-Zn towards HzOR and HER.Unfortunatedly,due to poor catalytic performance and complex synthrsis processes.the bifunctional employment of Ni-Zn for both HER and HzOR has not been reported yet and is still a critical challenge.Therefore,a strategy of bubble-template electrodeposition was employed to fabricate Ni-Zn alloy catalysts on Ni foam(NF)as highly effective and stable bifunctional catalysts towards HER and HzOR,an overpotential of 76 mV to achieve 10 mV cm-2 can be seen for HER,and the Tafel slope is only 49.3 mV dec-1,For HzOR,a high current density of 620 mA cm-2 at 0.4 V observed,and the Tafel slope rate is 44.5 mV dec-1,When assembled as a symmetric electrolyzer using the as-prepared Ni-Zn electrodes as both cathode and anode to simultaneously catalyze HzOR and HER,the Ni-Zn couple displays excellent cell performances with an extremely low cell voltage of 0.167 V、0.497 V and 0.789 V to attain 10、100 and 200 mA cm-2 respectively.In order to further enhance the catalytic performance,a Ni-Zn/rGO catalyst was prepared in this paper.The results show that the catalytic has a significant improvement compared with the Ni-Zn,and at the optimal NiZn ratio,for hydrogen evolution reaction(HER),an overpotential of 49 mV is required to reach a current density of 10 mA cm-2,and the Tafel slope is 26.3 mV dec-1,For hydrazine oxidation,the current density of Ni-15 at.%Zn/rGO was 744 mA cm-2 at 0.4 V with a Tafel slope of 33.5 mV dec-1.Simultaneously,the characterization and electrocatalytic activity of Ni-Zn and Ni-15 at.%Zn/rGO after long term stability was tested.The surface porous structure with nanosheet arrays were well maintained attribute to the almost unchanged catalytic activity.The adhesion test is carried out to test the gas release processes,and the porous structure of Ni-Zn catalyst can significant reduce the contact sites of catalysts with produced N2 and H2,leading to fast removal rate of N2 and H2 gas bubbles.更多还原