高分散Co_(0.2)Ni_(1.6)Fe_(0.2)P助催化剂改性P掺杂g-C_(3)N_(4)纳米片高效光催化析氢的研究

P-Doped g-C3N4 Nanosheets with Highly Dispersed Co_(0.2)Ni_(1.6)Fe_(0.2)P Cocatalyst for Efficient Photocatalytic Hydrogen Evolution

随着化石燃料使用的增加和温室气体排放量持续上升,20世纪以来气温上升得更快。开发环境友好型能源取代传统化石燃料是当务之急。氢能源作为-种清洁、高效的能源,被认为是最有希望取代传统化石燃料的能源。光催化水分解水产氢作为为一种环保型技术被认为是最有前景的氢能生产方法。提高光生电子-空穴对分离效率是构建高效光催化剂的关键。然而,利用高度分散的助催化剂构建高效、稳定的产氢光催化剂仍然是-一个挑战。本文首次成功地采用--步原位高温磷化法制备了高度分散的非贵金属三金属过度金属磷化Co_(0.2)Ni_(1.6)Fe_(0.2)P助催化剂(PCNS-CoNiFeP)掺杂P的石墨相氮化碳纳米片(PCNS)。有趣的是,PCNS-CoNiFeP与传统氢氧前驱体磷化法制备的CoNiFeP相比,没有聚集性,分散性高。X射线衍射(XRD).X射线光电子能谱(XPS).元素映射图像和高分辨率透射电镜(HRTEM)结果表明,PCNS-CoNiFeP已成功合成。紫外-可见吸收光谱结果表明,PCNS-CoNiFeP在200--800 nm波长范围内较PCNS略有增加。光致发光光谱、电化学阻抗谱(EIS)和光电流分析结果表明,CoNiFeP助催化剂能有效促进光生电子空穴对的分离,加速载流子的迁移。线性扫描伏安法(LSV)结果还表明,负载CoNiFeP助催化剂可大大降低CNS的过电位。结果表明,以三乙醇胺溶液为牺牲剂的PCNS-CoNiFeP最大产氢速率为1200 μmol-h^(-1).g^(-1),是纯CNS-Pt(320 μmol-h^(-1).g^(-1))的4倍。在420 nm处的表观量子效率为1.4%。PCNS-CoNiFeP在光催化反应中也表现出良好的稳定性。透射电镜结果表明,6-8 nm的CoNiFeP高度分散在PCNS表面。高度分散的CoNiFeP比聚集的CoNiFeP具有更好的电荷分离能力和更高的电催化析氢活性。由此可见,聚合的CoNiFeP-PCNs(300 μmol-h^(-1).g^(-1))的产氢速率远低于PCNS-CoNiFeP.此外,CNS的P掺杂可以改善其电导率和电荷传输。

Throughout the twentieth century,temperatures climbed rapidly as the use of fossil fuels proliferated and greenhouse gas levels soared.Thus,the need to develop environmentally friendly energy sources to replace traditional fossil fuels is urgent.Clean and highly efficient,hydrogen is considered the most promising energy source to replace traditional fossil fuels.The production of hydrogen by photocatalytic water splitting is environmentally friendly,and is considered the most promising method for producing hydrogen energy.Enhancing the separation efficiency of photogenerated electron-hole pairs has been identified as a key milestone for constructing high-efficiency photocatalysts.However,the construction of efficient and stable hydrogen-evolution photocatalysts with highly dispersed cocatalysts remains a challenge.Here,we succeeded,for the first time,in fabricating P-doped CNS(PCNS)with a highly dispersed non-noble trimetallic transition metal phosphide Co_(0.2)Ni_(1.6)Fe_(0.2)P cocatalyst(PCNS-CoNiFeP),by a one-step in situ high-temperature phosphating method.Remarkably,the CoNiFeP in PCNS-CoNiFeP demonstrated no aggregation and high dispersibility compared with CoNiFeP prepared by the traditional hydroxide-precursor phosphating method(PCNS-CoNiFeP-OH).X-ray diffraction,X-ray photoelectron spectroscopy,element mapping images,and high-resolution transmission electron microscopy results demonstrate that PCNS-CoNiFeP was successfully synthesized.The UV-Vis absorption results indicate a slight increase in absorbance for PCNS-CoNiFeP in the 200–800 nm wavelength region compared with that of PCNS.Photoluminescence spectroscopy,electrochemical impedance spectroscopy,and photocurrent results demonstrated that CoNiFeP cocatalysts could effectively promote the separation of photogenerated electron-hole pairs and accelerate the migration of carriers.The linear sweep voltammetry results also demonstrate that the CoNiFeP cocatalyst loading could significantly decrease the overpotential of CNS.Therefore,the maximum hydrogen evolution rate of PCNS-CoNiFeP was 1200μmol·h^(-1)·g^(-1),which was approximately four times higher than that of pure CNS-Pt(320μmol·h^(-1)·g^(-1))when using TEOA solution as a sacrificial agent.The apparent quantum efficiency of PCNS-CoNiFeP was 1.4%at 420 nm.The PCNS-CoNiFeP also exhibited good stability during the photocatalytic reaction.In addition,the TEM results indicate that CoNiFeP with a size of 6–8 nm are highly dispersed on the PCNS surface.The highly dispersed CoNiFeP demonstrated better charge-separation capacity and higher intrinsic electrocatalytic hydrogen-evolution activity than the aggregated CoNiFeP.Thus,the hydrogen evolution rate of aggregated CoNiFeP-PCNs(300μmol·h^(-1)·g^(-1))was much lower than that of PCNS-CoNiFeP.Furthermore,P doping of CNS could improve electric conductivity and charge transport.It is expected that loading highly dispersed CoNiFeP and P doping could be extended to promote photocatalytic hydrogen production using various photocatalysts.