| Large-scale production of hydrogen,which is known as cleanly and high-energy renewable energy sources,is the key to promote the development of hydrogen economy.Hydrogen production by electrochemical water splitting via hydrogen evolution reaction(HER)on cathodes is a promising pathway to convert sustainable electricity from solar,water and wind into chemical energy.However,the theoretical reversible potential of the water splitting reaction of 1.23 V is lower than that of the conventional water-alkali electrolyzers(1.8?2.0 V.)It has been long known that platinum-based catalysts can dramatically reduce the electrolysis overpotentials and speed up the kinetics of HER for high efficiency water splitting.Nevertheless,the practical implementation of hydrogen production is limited by the high costs and natural scarcity of these noble metal catalysts.Developing low-cost noble-metal-free catalysts is becoming the current subject of intense investigation.Among them,Tansition metals and alloys with low price and abundant has attracted much attention due to their unique electronic structure and relatively high catalytic activity.The preparation of catalytic electrodes usually requires binder and support,which has a serious effect on the catalytic performance of electrodes because of the presence of interface resistance.Self-standing nanoporous metals can be prepared by dealloying with the merits of good electrical conductivity,high specific surface area,tunable pore size and so on.It can be directly used as a catalytic electrode for HER and effectively solve the interface problem.In this study,the structure of electrode(dealloying nanocrystalline)and electrode composition(solid solution doping)were designed to prepare high efficient and stable self-supporting nanoporous Ni-based alloy electrodes.Binary NiMn,ternary NiMnFe and quaternary NiMnFeMo alloys and their corresponding three-dimensional self-supporting nanostructures were investigated.The research mainly contains as follow:The binary NiMn,ternary NiMnFe and quaternary NiMnFeMo alloy ribbons are successfully prepared according to the phase diagram and "volcano plot".The SEM/EDS tests show they are uniform composition and regular morphology.The ribbons are FCC solid solution by XRD analysis,which is helpful to form uniform three-dimensional(3D)nanoporous structure.The catalytic properties of different alloy systems were tested by LSV.With increase of different radii element types,the mixing entropy and dislocation increased.While,the overpotential of the corresponding material is decreased.Under the macroscopic condition,the material also had a symmetrical structure of face-centered cubic.The DOS theory showed the conductivity of materials were improved.Therefore the catalytic performance of corresponding material is improved.The free-standing nanoporous alloy materials was prepared by one-step process of dealloying.SEM/TEM test showed that 3D and bicontinuous structure were successfully prepared.The pore size of BET analysis was about 2?8 nm,which was consistent with TEM test.XRD analysis indicated that the nanoporous alloys still keep a symmetrical structure of face-centered cubic.The catalytic performance of the obtained nanoporous materials in alkaline solution is tested.The activity of nanoporous NiMn is lower than that of NiMnFe,which possesses same structure and mopholopy prepared by dealloying.The main reason is that Fe element absorbs the surrounding oxygen in the catalytic process to prevent the formation of nickel oxide.Due to the synergistic effect of Mo,Fe/Ni in the quaternary nanoporous alloy,the performance of nanoporous NiMnFeMo alloy electrode is optimized with an overpotential of 128 mV at current density of 100 mA/cm~2.Meanwhile,it also has excellent catalytic performance for oxygen evolution reaction.It can be used as a bifunctional electrocatalyst for water splitting and work steadily for more than 10 hours at a certain current density(10 mA/cm~2)corresponding to the voltage of 1.53 V. |
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