摘要
使用有机物氧化替代电解水析氧可以降低电解水析氢的过电位,获得更有价值的有机物,并提高能量利用率,因此,研究提高催化剂催化性能并研究机理具有重要意义。通过共沉积后退火煅烧的简单处理方法,将Ni引入Co基尖晶石中形成镍钴双金属尖晶石(Ni_(1.5)Co_(1.5)O_(4))。Ni_(1.5)Co_(1.5)O_(4)维持了原有的纳米片结构和尖晶石物相且Ni与Co之间存在电荷转移。相比于原始材料Co_(3)O_(4)和NiO,Ni_(1.5)Co_(1.5)O_(4)具有更低的起始电位和更高的HMF转化率、FDCA产率和法拉第效率。Ni在催化过程中与HMF存在动态演化,而Co在HMFOR中不仅具有催化活性还有维持催化剂构型稳定的作用。
[Background and purpose]At present,the synthesis of FDCA from HMF mainly relies on the traditional liquid-phase catalytic reaction system.This reaction process requires the use of not only noble metal catalysts,such as platinum(Pt),gold(Au)and palladium(Pd),but also toxic strong oxidants,such as potassium dichromate(K_(2)Cr_(2)O_(7))or potassium permanganate(KMnO_(4)).The reaction conditions are rather harsh,usually requiring relatively high temperatures(100–200℃)and high pressures(>5 bar)to effectively achieve the conversion of HMF.Therefore,efforts have been constantly made to seek more environmentally friendly and economical methods.Electrocatalysis,as an emerging technology,can be used for the conversion of HMF under milder conditions,while avoiding the use of toxic oxidants and noble metal catalysts.Noble metal catalysts exhibit certain performance in the electrocatalytic conversion of HMF,but their high cost and scarce raw materials are significant drawbacks.Therefore,the development of highly efficient and inexpensive non-noble metal catalysts has become a research hotspot in the field of biomass conversion.[Methods]Electrodeposition method was used to synthesize the catalysts.In an electrolyte with a total metal salt concentration of 50 mmol·L^(-1),hydroxides of nickle-cobalt and other elements(Ni-Co-OH)were formed on titanium mesh substrate.After electrodeposition for 10 min,a blue-cyan NiCo hydroxide sample was obtained.Subsequently,the sample was calcined at 250℃for 2 h in air,at a heating rate of 1℃·min^(−1),converting the bimetallic cobalt-based hydroxide into Ni_(x)Co_(y)O_(4).Electrocatalytic oxidation activity of HMF of the Ni_(1.5)Co_(1.5)O_(4) catalyst could be optimized by adjusting the ratio of nickel.The regulation of Ni content could be used to enhance the conductivity of the catalyst,increase the number of active sites and adjust the electron density and energy-level distribution in the spinel structure,thereby improving the HMFOR activity.In situ Raman and in-situ EIS were combined to explore the mechanisms and roles of Ni and Co in Ni_(1.5)Co_(1.5)O_(4) during the catalysis of HMFOR.[Results]Benefiting from the flexible metal-ion substitution mechanism and structural stability of the Co-based spinel,Ni_(1.5)Co_(1.5)O_(4) exhibited nanosheet morphology and large specific surface area.There is an inter-ionic charge transfer between Ni and Co.In Ni_(1.5)Co_(1.5)O_(4),electrons transfer from Ni to Co,making Co an electron-rich center and Ni an electron-deficient center.Secondly,the introduction of Ni increased the electrochemical active surface area of Ni_(1.5)Co_(1.5)O_(4) and the charge-transfer efficiency inside the electrode,thus improving the performance and efficiency of HMFOR.Eventually,a HMF conversion rate of 99.77%,a FDCA yield of 98.10%,and a Faradaic efficiency of 97.86%were achieved.[Conclusions]For Ni_(1.5)Co_(1.5)O_(4),on one hand,the Co-based spinel structure inherently possessed high structural stability.With the substitution of Ni ions,no significant lattice distortion or structural collapse occurred.On the other hand,Ni ions and Co ions are similar in size and charge,Ni ions can flexibly replace Co ions at different sites without disrupting the overall lattice structure.As a result,the nanosheet structure of the Co-based spinel is well-maintained,thus leading to increase in electrochemical specific surface area and number of active sites.There is an inter-ionic charge transfer between Ni and Co,rendering Co an electron-rich center and Ni an electron-deficient center.At applied voltages,Co^(3+)is more likely to be oxidized to generate highly active Co^(4+)for HMF.This active species key to the-OH—-CHO reaction.The results of in-situ Raman spectra indicated that the surface of Ni_(1.5)Co_(1.5)O_(4) underwent reconstruction at applied voltages.The formation of Ni^(3+)/Ni^(4+)at relatively high applied voltages led to a competitive reaction between the oxygen evolution reaction(OER)and HMF.In the synergistic effect of Ni and Co,apart from contributing catalytic activity,Co also played a role in maintaining the structural stability of the catalyst.
作者
韩世兴
方中海
李小雄
林菲菲
肖朝辉
HAN Shixing;FANG Zhonghai;LI Xiaoxiong;LIN Feifei;XIAO Zhaohui(School of Materials Science and Engineering,Hainan University,Haikou 570228,Hainan,China)
出处
《陶瓷学报》
北大核心
2025年第1期116-128,共13页
Journal of Ceramics
基金
国家自然科学基金(22302051)
海南省自然科学基金(223QN186)。
关键词
钴基尖晶石
5-羟甲基糠醛
电催化
反应机理
原位表征
cobalt-based spinel
5-hydroxymethylfurfural
electrocatalysis
reaction mechanism
in situ characterization
