有許多研究指出NiFe觸媒與Ni觸媒相比在產氧反應(oxygen evolution reaction, OER)的效率有倍數級的提升，而最近的研究更是指出把Mo加入NiFe中會讓效率更好，不過協同作用原理仍然未知。這是因為不同Mo組成所造成的內在活性在過去的文獻中產生衝突，所以目前鉬與第一排過度金屬的作用仍未知。因此我們通過調節電鍍液中NiFeMo的比例，並在銅箔上進行電沉積，製備了不同成分NiFeMox觸媒。 Mo組成為9％至26％，標示為NiFeMo1.5〜NiFeMo5.5。本研究中，我們將NiFeMo觸媒與NiFe觸媒對OER的活性進行比較，結果表明NiFeMo3.5和NiFeMo2.5的活性更好，而NiFeMo4.5具有與NiFe相似的Tafel斜率和起始電位。在這裡我們通過X射線光電子能譜 (XPS)、X光繞射圖譜 (XRD) 、掃描電子顯微鏡 (SEM)、掃描透射電子顯微鏡 (STEM)、高解析穿透式電子顯微鏡(HRTEM)和拉曼(Raman)光譜分析觸媒的表面性質。在電沉積的過程中Mo6+的參與，將促進Ni氧化成Ni2+，Fe氧化成Fe3+，並使成長的晶粒尺寸變小，結晶度上升。因為Mo是一種通用的配位體，所以Mo6+吸引電子形成Mo4+同時讓Ni和Fe氧化成Ni2+和Fe3+而且使得Fe3+的結合能上升。為了揭示加入鉬對OER的影響，我們進行的原位拉曼光譜，鉬會在OER之前先被氧化並發生重組，形成MoO6 (八面體結構) 和MoO42- (四面體結構)。 MoO6會與FeO6共享氧邊緣並使其不穩定。另一方面，MoO42-將與NiO6和FeO6鍵結，使Ni-O 和Fe-O產生扭曲，同時Mo傾向吸收電子將使Ni更容易氧化成Ni2+和Ni3+同時調節Ni2+/Ni3+的氧化還原電位，使NiFeMo羥基氧化物更容易生成。這表示MoO42-可以調節Fe-O和Ni-O的鍵結強度促使高價態的Fe3+和Ni3+更穩定，進而最適化OER中間體的吸附能。所以NiFeMo觸媒展現了良好的內在活性並且降低起始電位至1.47 V vs. RHE和Tafel斜率至42 mV/dec。

NiFeMo has been an attract catalyst for oxygen evolution reaction (OER), molybdenum shown the synergetic effect with first row 3d metal and enhances the water splitting efficiency. But the role of Mo has remained under debate. Due to the intrinsic effect of different composition of Mo based catalysts conflicted in the past report. So, we fabricate different compositions of NiFeMox catalysts by electrodeposition on Cu foils via modulated the ratio of Ni, Fe and Mo in the electrolytes. Mo compositions were from 9 % to 26 % assign to NiFeMo1.5 ~ NiFeMo5.5. The OER activity was compared to NiFe catalysts, which shown that NiFeMo3.5 and NiFeMo2.5 enhances the activity of OER and NiFeMo4.5 has the similar Tafel slope and onset potential with NiFe. Here we investigated the pre-catalyst surface properties by X- ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), X-ray diffraction (XRD), scanning transmission electron microscope (STEM), high resolution transmission electron microscope (HRTEM), and Raman spectra. Accompanying Mo6+ in the deposition process, promoting the Ni oxidized to Ni2+ and Fe oxidized to Fe3+ and the particles size become smaller and the crystallinity increase. Due to, Mo is a versatile coordination host, which draws in the electrons to formed Mo4+ and enhance the both Ni2+ and Fe3+ valance state. To revealing the role of Mo toward OER. We conduct the operando – Raman, Mo will be oxidized first before the OER and occurred the reorganization formed the MoO6 (octahedral structure) and MoO42- (tetrahedral structure). MoO6 will share the oxygen edge with FeO6 and destabilized it. On the other hand, MoO42- will bond with Ni and Fe, which will distorted the Ni-O and Fe-O, meanwhile Mo withdraws the electrons and promoting Ni oxidized to Ni2+ and Ni3+ and modulates the redox of Ni2+/Ni3+, leading the formation of the NiFeMo(oxy)hydroxide. It represents that MoO42- modulates Fe-O and Ni-O bond strength and stabilized the Fe3+ and Ni3+ and results in optimizing the adsorption energy of OER intermediates and lower onset potential and Tafel slope. NiFeMo3.5 show the onset potential at 1.47 V vs. RHE, and Tafel slope equal to 42 mV/dec.

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