Preparation And Properties Of Oxygen Electrode Catalyst For Energy Devices

Using renewable energy to produce hydrogen by water electrolysis is currently the most promising scheme for promoting sustainable and clean hydrogen economic development.Proton exchange membrane（PEM）water electrolysis is widely considered as one of the most appealing hydrogen production technologies for its high energy efficiency,high yield,and purity.Nevertheless,the overall efficiency is affected by the slow kinetics of the oxygen evolution reaction（OER）occurring at anode with four electron transfer,resulting in significant energy losses.In addition,the intermittent characteristics of renewable energy power generation technology make the energy conversion efficiency of power plants low,and there are phenomena of wind and electricity abandonment.Zinc air batteries with high efficiency energy storage can effectively solve this problem.However,its energy efficiency is limited by the sluggish kinetics of oxygen reduction reaction（ORR）occurring at cathode with four electron transfer samely.Therefore,developing superior catalysts is one of the effective ways to improve the energy efficiency of proton exchange membrane electrolyzers and zinc air batteries.Based on this,the main research contents of this paper are as follows:（1）Preparation and performance study of carbon supported ultra low metal content electrocatalysts.An electrocatalyst with low metal content（MnFe/NC）was used for alkaline ORR prepared through pyrolysis and desorption with a bimetallic organic framework as a precursor.SEM image showed that the element manganese is advantageous to improve thermal stability of the catalys,keeping the dodecahedral morphology after high temperature annealing.The comprehensive analysis of TEM image,X-ray photoelectron spectroscopy and powder X-ray diffraction shows that the metal content is extremely low,and the main active component is iron.At once the maintenance of the dodecahedral morphology accelerates mass transfer,which is conducive to improving performance.Despite the metal component content is relatively low,materials still exhibits excellent activity,reaching a half wave potential of 0.9 V,exceeding 0.85 V of commercial Pt/C.Under a voltage of 0.8 V,it can operate stably for more than 17 hours.In subsequent zinc air battery tests,it showed an energy density higher than Pt/C.（2）Preparation and performance exploration of Nd₆Ir₂O₁₃ electrocatalyst for acidic oxygen evolution reaction.A novel Nd₆Ir₂O₁₃ electrocatalyst was synthesized by a solid-state reaction and applied to acidic OER for the first time.During the OER process,combined with XPS analysis,it was concluded that the surface Nd atoms were leached to form active hydrated IrO_x as OER active sites,and meanwhile the coordinated environment of Ir remained relatively stable.Benefiting from the low Ir content（26.4 wt%）,Nd₆Ir₂O₁₃provides a mass activity of 123.5 mA/mg _Ir at an overpotential of 300 mV,about 42 times that of commercial IrO₂.Notably,Nd₆Ir₂O₁₃ requires an extremely low overpotential of 291mV to reach a current density of 10 mA cm^-2 and it can stable operate over 70,000 s,far exceeding the benchmark IrO₂ and most electrocatalysts for acidic OER.Combining it with Pt/C for water splitting test,only 1.51 V is needed to obtain 10 mA cm^-2.（3）In situ activation endows orthorhombic fluorite-type samarium-iridium oxide-enhanced acidic water oxidation catalyst IrO_x/Sm₃IrO₇ electrocatalyst preparation and performance study.The orthorhombic fluorite-type samarium-iridium oxide（Sm₃IrO₇）catalyst was synthesized by a simple solid-state reaction.After in situ activation,the as-prepared Sm₃IrO₇ exhibited higher catalytic activity,durability,and mass activity than commercial IrO₂.In-depth analysis revealed that during the in-situ activation process,amorphous IrO_x species were formed on the surface and evolved into a new heterostructure IrO_x/Sm₃IrO₇ with simultaneous Sm leaching.More importantly,the strong electronic interaction between the nascent IrO_x species and the remaining Sm₃IrO₇ leads to the compression of the Ir–O bonds in IrO_x compared with commercial IrO₂,thereby lowering the energy barrier of the oxygen evolution reaction.Based on the above analysis,it is speculated that the actual active substance that enhances acidic water oxidation should be IrO_x/Sm₃IrO₇.Theoretical calculations confirmed that the optimal energy level path of IrO_x/Sm₃IrO₇ follows the lattice oxygen mechanism.