Investigation On Fabrication And Electrocatalytic Properties Of Noble Metal Based Nanoporous Nanowires Materials

The upcoming global energy crisis and issues concerning environment pollution have made clean electrochemical energy conversion and storage technologies the need of the hour.Having high efficiency and environmental benignity,direct fuel cells(DFCs)have attracted worldwide attention due to their potential applications in portable devices and automotive systems.As an important anode fuel of DFCs,hydrogen is being vigorously pursued as a future energy source,which has greatly inspired the development of electrochemical water splitting technique.However,these energy conversion devices inevitably use noble metals to catalyze electrode reactions at both the anode and cathode,which severely limit their practical applications.The creation of nanostructured noble metal based alloy provides an available way to overcome these limitations via optimizing catalytic performances,while reducing the usage of expensive noble metals.Based on microalloying and solidification control,we proposed a novel eutectic-directed self-templating strategy to prepare a series of noble metal based nanoporous nanowires via the combination of rapid solidification and dealloying.The Al3Ni fibrous(rod-like)intermetallic phase in Al-Al3Ni eutectic alloys displays highly morphological similarity with one-dimensional nanowires.Inspired by this,we successfully fabricated Ni@NiO core-shell nanoporous nanowires(NPNWs)through chemical dealloying of a rapidly-solidified Al96Ni4 fibrous eutectic alloy.On this basis,we have delicately designed Al97.8Ni2Pt0.2 precursor alloy,Pt was introduced into Al3Ni fibrous intermetallic compound phase forming Al3(Ni,Pt)phase through the eutectic reaction.The fibrous structure was inherited and further refined through subsequent dealloying process to get the final PtNi NPNWs.The PtNi NPNWs exhibit superior electrocatalytic activity(5-fold enhancement in the specific activity)and enhanced durability towards oxygen reduction reaction(ORR),as benchmarked with commercial Pt/C.Both the RDE and RRDE results demonstrate that the ORR on the PtNi surface follows a four-electron pathway.Density functional theory calculations verify the 4e-pathway of PtNi in ORR and rationalize the activity enhancement on the basis of adsorption energy,d-band center,thermodynamics,and kinetics through density functional theory calculations.On this basis,trimetallic PdPtNi NPNWs have been successfully fabricated through the combination of rapid solidification and two-step dealloying method.The electrochemical test shows that PdPtNi alloy exhibit superior catalytic activities for ethylene glycol and glycerol electrooxidation(EG/GOR)in an alkaline solution.Compared to PdNi and PtNi NPNWs,the PdPtNi NPNWs display higher specific and mass activity,better anti-poisoning property and stability.The ECSA-nomarlized specific activities of PdPtNi NPNWs for EGOR and GOR are 2.7 and 2.9 times that of the commercial Pt/C catalyst,respectively.The superior electrocatalytic performance of PdPtNi NPNWs can be attributed to the alloying effect favoring the electronic structure interaction for the optimized activity,promotion impact of Ni to poisoning species oxidation,1D morphology facilitating the electron transport,and nanoporous structure promoting the electrolyte diffusion.This strategy can be further extended to the preparation of multi-component alloys.By rapid solidification and subsequent different dealloying processes,two multi-component nanoporous alloys(PtPdRhIrNi(D-SN)and NiPtPdRhIrAl(D-SS))with different compositions have been obtained from the Al97.6Ni2Pt0.1,Pd0.1Rh0.1Ir0.1 precursor.The electron microscope results confirm that the as-dealloyed sample with unique nanoporous nanowires was obtained.Compare with PtPdRhlrNi NPNWs,the nanowire length of NiPtPdRhIrAl NPNWs is longer and the ligment size of NiPtPdRhIrAl NPNWs is larger,which are related to the different corrosion rate of Ni and the different diffusion rate of precious metals on solution/alloy surfaces in different corrosion conditions.The electrochemical measurements indicate that there are obvious differences of HER activities between the two alloys in both acidic and alkaline electrolytes.Among them,PtPdRhlrNi nanoporous nanowires(dealloyed in 1 M NaOH and 2 M HNO3 solutions)yield the better electro-catalytic performance towards HER,and the overpotential at 10 mA cm-2 is 22 mV in 0.5 M H2SO4 and 55 mV in 1.0 M KOH electrolyte,respectively.The superior electrocatalytic performance of PtPdRhIrNi sample can be attributed to structure effect,alloy effect and high entropy effect.In addition,Iridium-based alloys are excellent candidates for catalyzing oxygen evolution reaction.Based on alloy design and microalloying,a series of IrM(M = Ni,Co or Fe)catalysts with unique nanoporous nanowires structure have been successfully fabricated through the combination of rapid solidification and two-step dealloying method.The electrochemical measurements indicate that the as-obtained IrM NPNWs show fairly high activity as acidic OER catalysts.In addition,the catalytic activities of IrM nanowires show a transition metal dependent feature,among which IrNi delivers the best activity with an exceptionally low overpotential(283 mV at 10 mA cm-2)and a high mass activity(0.732 A mg-1 at 1.53(V vs.RHE)).This performance is much higher than that of commercial IrO2 and most of the state-of-the-art Ir-based acidic catalysts.Density functional theory calculations verify that the weaker adosorption energy of oxygen-based intermidiates on IrMOx(110)is the reason for the superior catalytic activity of IrM NPNWs.In addition,density functional theory calculations rationalize the 3d transition metal dependent catalytic activity of IrM electrocatalysts,wherein the ligand effect gives rise to the downshift of d-band center and thus weakens the adsorption of oxygenated intermediates.