MoP-NC纳米球负载Pt纳米粒子用于高效甲醇电解.pdf

物 理 化 学 学 报 Acta Phys.-Chim.Sin.2023,39(9),2301005(1 of 10)Received:January 3,2023;Revised:February 7,2023;Accepted:February 8,2023;Published online:February 24,2023.*Corresponding author.Email:;Tel.:[phone].The project was supported by the National Natural Science Foundation of China(21972124,22102105,22272148).国家自然科学基金(21972124,22102105,22272148)资助项目 Editorial office of Acta Physico-Chimica Sinica Article doi:10.3866/PKU.WHXB202301005 MoP-NC Nanosphere Supported Pt Nanoparticles for Efficient Methanol Electrolysis Meng Li 1,Fulin Yang 1,Jinfa Chang 2,Alex Schechter 3,Ligang Feng 1,*1 School of Chemistry and Chemical Engineering,Yangzhou University,Yangzhou 225002,Jiangsu Province,China.2 NanoScience Technology Center,University of Central Florida,Orlando,FL 32826,USA.3 Department of Chemical Sciences,Ariel University,Ariel 40700,Israel.Abstract:Hydrogen energy is a potential energy storage carrier due to its advantages of cleanliness,high efficiency and renewability.Electrocatalytic water splitting is an ideal method to generate hydrogen,and the slow kinetics of water oxidation,namely,oxygen evolution reaction(OER),greatly restricts its practical application.To reduce the energy consumption required for OER,methanol oxidation reaction(MOR)with a much lower theoretical potential is very promising to replace OER to assist hydrogen generation.The theoretical potential of MOR is only 0.016 V vs.SHE(standard hydrogen electrode),which is much lower than that of OER(1.23 V),and the energy-saving can be about 60%compared to that of traditional water electrolysis.Therefore,using MOR instead of OER to realize methanol electrolysis for hydrogen production is an effective way to reduce energy consumption.An efficient bifunctional catalyst is very important for green hydrogen generation from overall methanol electrolysis.Currently,Pt-based materials are still the best catalyst for hydrogen evolution reaction(HER)and MOR,while they are more challenging in the MOR as they are prone to intermediates poisoning during the catalytic reactions.The introduction of transition metal-based promoters such as phosphides is an effective strategy to promote the catalytic ability for methanol oxidation.Herein,ultrafine Pt nanoparticles with an average particle size of 2.53 nm evenly grown on MoP-NC nanosphere(Pt/MoP-NC)were demonstrated as an efficient electrocatalyst for methanol electrolysis towards hydrogen generation.The introduction of MoP-NC nanospheres support not only restricts the aggregation of Pt,but also improves the catalytic performance and anti-poisoning ability.Specifically,Pt/MoP-NC catalyst exhibited high methanol oxidation performance with a peak current density of 90.7 mAcm2,which was 3.2 times higher than that of commercial Pt/C catalysts,and good hydrogen evolution reaction performance with a low overpotential of 30 mV to offer 10 mAcm2 in an acid medium,which was comparable to commercial Pt/C.The assembled Pt/MoP-NC|Pt/MoP-NC electrolyzer showed a cell voltage of 0.67 V at 10 mAcm2,ca.1.02 V less than that of the overall water splitting system(1.69 V).The high catalytic ability of Pt/MoP-NC originated from the electronic effect between noble metal active center Pt and the adjacent MoP-NC support with a unique layered porous spherical structure.The partial electron transfer from MoP to Pt can lower the d-energy band center of Pt,which weakened the binding energy between Pt and adsorbed toxic intermediates.In addition,the oxophilic MoP-NC nanospheres can activate water to provide more hydroxyl species and facilitate the oxidative removal of CO intermediates adsorbed on the Pt active sites.The current work might inspire the design and preparation of novel catalyst platforms for methanol electrolysis in hydrogen generation.Key Words:Electronic effect;Methanol electrolysis;Transition metal phosphides;Platinum-based catalyst;Bifunctional catalyst 物理化学学报 Acta Phys.-Chim.Sin.2023,39(9),2301005(2 of 10)MoP-NC 纳米球负载纳米球负载 Pt 纳米粒子用于高效甲醇电解纳米粒子用于高效甲醇电解 李萌1，杨甫林1，常进法2，Alex Schechter 3，冯立纲1,*1扬州大学化学化工学院，江苏 扬州 225002 2 NanoScience Technology Center,University of Central Florida,Orlando,FL 32826,USA.3 Department of Chemical Sciences,Ariel University,Ariel 40700,Israel.摘要：摘要：实现绿色甲醇电解制氢需要高效的双功能催化剂。本文采用热处理结合乙二醇还原法成功制备了MoP-NC纳米球负载的超细Pt纳米粒子(平均粒径为2.53 nm)复合催化剂(Pt/MoP-NC)用于高效甲醇电解制氢。MoP-NC纳米球不仅能提高Pt纳米粒子的分散性并且增强Pt的抗中毒能力。电化学测试表明Pt/MoP-NC催化剂在酸性甲醇氧化反应(MOR)和析氢反应(HER)中具有较高的催化性能；其中，MOR的正向扫描峰值电流密度为90.7 mAcm2，是商业Pt/C催化剂的3.2倍，在10 mAcm2的电流密度下，HER的过电位低至30 mV，与商业Pt/C接近。由Pt/MoP-NC|Pt/MoP-NC组装的两电极电解槽驱动10 mAcm2的电流密度仅需要0.67 V的电压，比相同条件下电解水的电压低1.02 V，大大降低了能量输入。Pt/MoP-NC的高催化性能主要来源于Pt活性中心与相邻层状多孔球形结构的MoP-NC载体之间电子效应及配体效应引起的抗一氧化碳中毒能力的提升和含氧物种的容易生成。关键词：关键词：电子效应；甲醇电解；过渡金属磷化物；铂基催化剂；双功能催化剂 中图分类号：中图分类号：O646 1 Introduction The energy crisis induced by a large amount of fossil fuel consumption has accelerated the development of sustainable and environment-friendly energy sources such as solar,and wind energy 14.While the intermittence of these energies cannot meet the practical application,and thus,they should be transferred to proper energy for storage 5,6.Hydrogen as a recyclable and clean energy is considered the best form,which can be produced by these sustainable energies via the water splitting technique.Therefore,electrochemical water splitting for hydrogen production has received much attention 7,8.The thermodynamic potential for water splitting is 1.23 V under standard conditions,and much higher energy input is required due to the high overpotentials generated during the electrocatalysis,especially for the complicated and sluggish anode oxygen evolution reaction(OER)9,10.To reduce the overpotential and make the whole reaction more energy efficient,an effective approach was proposed to replace the OER with an alternative reaction that can happen at low potentials 11,12.Among the possible reactions 1315,methanol oxidation,which has a thermodynamic potential of 0.016 V,has been demonstrated very promising to replace OER;and the corresponding methanol electrolysis would be more competitive for hydrogen generation,as claimed that the energy-saving can be about 60%compared to that of traditional water electrolysis 16,17.To realize efficient methanol electrolysis,high-performing catalysts are required to catalyze the methanol oxidation reaction(MOR)and hydrogen evolution reaction(HER)for methanol electrolysis 18.The Pt-based materials are still the best catalyst for these reactions 19,while it is more challenging in the MOR as they are vulnerable to intermediates poisoning during the catalytic reactions 2022.So,attention should be directed to the anode catalyst study;currently,it is an effective strategy to promote methanol oxidation of Pt by introducing transition metal-based promoters such as oxides and phosphides 22,23.For example,Pt/C/TiO2 catalyst showed good catalytic activity for MOR due to strong metal-support interactions between Pt nanoparticles and TiO2 nanotubes 24;in addition,TiO2 nanotubes could activate water to provide adsorbed OH intermediates(OHads)species in assisting the poisoning adsorbed CO intermediates(COads)removal on Pt sites via a bi-functional catalytic mechanism.The better CO tolerance of the Pt/FeP nanosheet hybrid was also attributed to the cooperative effect from the down-shifted d-band center of Pt induced by the special activity of Fe+and P 25.Molybdenum phosphide(MoP)has received special attention for water adsorption and dissociation due to the different electronegativities between Mo and P in MoP;specifically,the larger electronegativity of P-induced partial electron donation of Mo,where Mo can act as the hydride acceptor center and P works as the proton acceptor center 26,27.The good water activation ability highly inspired us for its potential assisting ability in MOR by combing with the Pt nanoparticles.However,the agglomeration of MoP nanoparticles is inevitable during their preparation in high-temperature conditions,which reduces the surface area exposure and metal-support effect 28,29.To overcome this problem,stabilizing the MoP by coupling with carbon materials would be an effective approach,which could prevent particle aggregation and increase conductivity 30.Considering the above condition and challenges,herein,the hybrid support of MoP-NC derived from the high-temperature phosphorization of polymerized dopamine hydrochloride and 物理化学学报 Acta Phys.-Chim.Sin.2023,39(9),2301005(3 of 10)ammonium molybdate tetrahydrate was employed to support the ultrafine Pt nanoparticles for overall methanol electrolysis.The ultrafine Pt nanoparticles with an average size of 2.53 nm were anchored over the MoP-NC nanospheres assembled from nanosheets;and the layered porous spherical structure imparted a strong synergistic interface effect between Pt and MoP,which promoted the catalytic activity and stability for the HER and MOR than the commercial Pt/C catalysts.The special promotion effect of MoP in the system was also demonstrated by comparing it to the traditional support of Mo-NC supported catalysts.When used as a bifunctional electrocatalyst for overall methanol electrolysis,a low cell voltage of 0.67 V was required to provide 10 mAcm2 with a 10 h durability,which was 1.02 V less than that for the traditional water electrolysis.The current work showed a novel catalyst platform for methanol electrolysis in hydrogen generation,and the results would clarify the promotion effect of MoP in the catalysis reaction.2 Experimental and computational section 2.1 Reagents All reagents are analytical grade and used without further purification.Ammonium molybdate tetrahydrate(NH4)6Mo7O244H2O),anhydrous ethanol,dopamine hydrochloride,ammonium hydroxide(NH3H2O),ammonium phosphate dibasic(NH4)2HPO4),ethylene glycol,platinum chloride acid(H2PtCl6,30 mgmL1),Nafion(5%(w,mass fraction),methanol(CH3OH)and sulfuric acid(H2SO4)were purchased from Shanghai Aladdin Bio-Chem Technology Co.,LTD.Milli-Q water(Thermo Fisher Scientific(USA)Co.,Ltd)was used to prepare the solutions.Commercial 20%(w)Pt/C catalyst(HiSPEC 3000)was purchased from Johnson Matthey company.2.2 Synthesis of Mo-PDA In a typical synthesis process,180 mg of(NH4)6Mo7O244H2O is dissolved in a mixed solution of 144 mL of ultrapure water and anhydrous ethanol(volume ratio 1:2),and then 180 mg of dopamine hydrochloride is added with stirring.After 10 min,0.6 mL of NH3H2O is quickly injected into the above solution.The color of the solution immediately changes from orange-yellow to orange-red.After continuous stirring for 6 h at room temperature,the Mo-PDA precursor was collected by centrifugation,washed three times with ethanol,and then dried overnight at 80 C in a vacuum chamber.2.3 Synthesis of MoP-NC The prepared Mo-PDA precursor was then carbonized in flowing Ar at 450 C for 1.5 h at a heating rate of 2 Cmin1.Subsequently,100 mg of carbonized material was mixed with 200 mg(NH4)2HPO4 and heated at 800 C under H2/Ar(5%)atmosphere for 2 h at a heating rate of 5 Cmin1.The resulting product is expressed as MoP-NC.2.4 Synthesis of Pt/MoP-NC 40 mg of MoP-NC was dispersed in 50 mL ethylene glycol,333 L H2PtCl6(30 mgmL1)was added with continued stirring.The mixture was heated in an oil bath at 140 C for 6 h.The suspension was naturally cooled to room temperature and washed several times with ultrapure water.The product was collected and dried in a vacuum oven at 60 C for 12 h.The product was named Pt/MoP-NC.Furthermore,the synthesis progress of Pt/Mo-NC is similar to that of Pt/MoP-NC,except that MoP-NC is replaced by Mo-NC(no phosphorus source is added during the synthesis process and the details can see the supporting information).2.5 Physical characterizations The sample was characterized on Bruker D8 advance X-ray diffraction(XRD)with Cu K radiation,and the corresponding crystal size of all catalysts was calculated according to Scherrer formula:D=K/(cos).Where K has a typical value of about 0.89 using Cu K radiation(=1.5405),is the full width at half maximum intensity of the peak and is the Bragg angle.The morphology was examined by scanning electron microscopy(SEM,Hitachi,S-4800 II,Japan).All transmission electron microscopy(TEM)and high-resolution TEM(HRTEM)measurements were conducted on a TECNAI G2 operating at 300 kV.The energy-dispersive X-ray detector spectrum(EDX)images were obtained on a TECNAI G2 transmission electron microscope equipped with an EDXA detector.X-ray photoelectron spectroscopy(XPS)measurements were carried on an ECSALAB250Xi spectrometer with an Al K radiation source.2.6 Electrochemical measurements All the electrochemical measurements were carried out in a conventional three-electrode electrochemical cell by using an electrochemical workstation(IVIUM-n-Stat).The saturated calomel electrode(SCE,Hg/Hg2Cl2)was used as the reference electrode.The samples were tested on a glassy carbon electrode(3.0 mm diameter)as a working electrode and a graphite rod as the counter electrode.The catalyst ink was prepared as follows.5 mg catalyst,50 L of 5%(w)Nafion solution was dispersed in 950 L of ethanol by sonication for at least 30 minutes to form a homogeneous ink(loading:0.08 mgPtcm2).Then 10 L of the catalyst ink was loaded onto a pre-cleaned working electrode and dried at room temperature(details see the Supporting Information).3 Results and discussion The catalyst of MoP-NC supported Pt nanoparticles(Pt/MoP-NC)was prepared involving three steps as shown in Scheme 1.Briefly,the polymerized Mo-polydopamine(Mo-PDA)nanosphere was first prepared from dopamine hydrochloride and(NH4)6Mo7O244H2O,and then MoP-NC was obtained by phosphorization of the thermal annealed product of Mo-NC,and final ly,Pt/MoP-NC catalyst was achieved by depositing Pt nanoparticles to the MoP-NC support via ethylene glycol reduction approach.A control sample of Mo-NC supported Pt nanoparticles was also fabricated and compared to demonstrate the effect of phosphide materials in the system.物理化学学报 Acta Phys.-Chim.Sin.2023,39(9),2301005(4 of 10)The morphology and microstructure evolution from the Mo-PDA precursor,MoP-NC to Pt/MoP-NC were first characterized by scanning electron mMicroscopy(SEM).The nanospheres assembled by nanosheets were found for the Mo-PDA precursor;a size of 600700 nm in diameter was observed(Fig.1a and S1(Supporting Information).After the thermal annealing carbonization and phosphorization process,the nanospheres assembled from nanosheets were still observed,but the exterior surface became coarser and the size was reduced(Fig.1b and S2).This was caused by the shrinkage and decomposition of the ligand during the transformation from Mo-PDA to MoP-NC 31.This structure and morphology were well inherited for Pt/MoP-NC catalyst(Fig.1c).The local structure of the Pt/MoP-NC catalyst was further observed by Transmission Electron Microscope(TEM).The nanosphere assembled by the nanosheets was clearly observed,where uniform deposition of Pt nanoparticles was visible on the extended surface(Fig.1d,and Fig.S3 fo