Preparations And Electrocatalytic Performances Of Doped Carbon Supported Nickel Iron-Containing Electrocatalysts As Oxygen Evolution Electrocatalysts

The ever-growing environmental problems caused by the energy crisis and the consumption of fossil fuels have resulted in an urgent search and development of clean,renewable,and alternative sources of energy.Hydrogen(H2)energy has attracted wide attention of researchers as a high-energy and sustainable eco-friendly energy source.The water electrolysis device is considered a facile and efficient method for hydrogen production.The entire electrolyzed water process is based on two half-reactions:the oxygen evolution reaction(OER)at the anode and the hydrogen evolution reaction(HER)at the cathode,both of which require an electrocatalyst to reduce its overpotential and increase efficiency.However,the OER reaction involves a four-electron transfer in alkaline media,which limits the reaction kinetics,results in a large overpotential and is regarded as a bottleneck in the water splitting.So far,noble metal(such as IrO2 and RuO2)still are the best catalysts with catalytic performances for OER,but their scarcity,exorbitant cost,and poor long-term stability in alkaline solutions have greatly limited their large-scale application.Therefore,considering the factors of price and practical application,it is important to develop non-noble metal OER catalysts with high efficiency and excellent stability.Although transition metal-based compounds have been used as potential catalysts to replace noble metals,their low electrical conductivity,instability,and limited active sites need to be solved.In this thesis,aiming to boost the high electrocatalytic activities,the heteroatom doped carbon supported nickel-iron-based transition metal phosphides and alloys composites for OER electrocatalysts were successfully prepared by combining a simple hydrothermal synthesis method and a subsequent calcination procedure The main research contents are presented as follows(1)Preparation of NiFeP@NPC composite and their electrocatalytic performances for OER.With the aid of the rich surface sites and charges of yeast to adsorb nickel ions and iron ions,a spherical porous nitrogen-phosphorus co-doped carbon-supported nickel-iron phosphide catalyst material(NiFeP@NPC)was obtained via a two-step protocol of hydrothermal synthesis and subsequent calcination.The advantages of the preparation lie at the use of yeast as a template not only provides spherical porous carbon,which is benefit to the transmission of electron;but also affords a phosphorus source to avoid a toxic phosphorization and thereby achieve a green and efficient synthesis method.The synergistic effect of transition metal phosphide and carbon matrix effectively improved the OER electrocatalytic activity,and the catalyst material exhibited excellent OER catalytic activity.Electrocatalytic testing shows that under alkaline conditions with an electrolyte of 1.0 M KOH,the overpotentials required to reach a current density of 10 mA cm-2 and 100 mA cm-2 were 321 mV and 389 mV,respectively.Furthermore,by adjusting the ratio of nickel/iron starting materials,the NiFeP@NPC composite with the optimized performance was obtained,i.e.,after 1000 cycles of CV for OER,?100 only decayed by 20 mV.(2)Preparation of Ni3Fe/PC composite and their electrocatalytic performances for OER.An anionic surfactant sodium dodecyl phosphate(SDP)intercalated hydrotalcite-like NiFe(OH)2 was used as a precursor,and a Ni3Fe alloy nanoparticle supported on a flower-like phosphorus doped carbon(Ni3Fe/PC)composite catalyst material was synthesized by a subsequent calcination reduction method.The advantages of the preparation include:(i)the simultaneously introduce carbon source,phosphorus source,and nitrogen source of the intercalated surfactant to obtain P-doped flower spherical carbon supported Ni3Fe materials,thereby improving the conductivity of the catalytic material.(ii)The carbon layer coating the alloy nanoparticles prevents the corrosion of the electrolyte and further improves its electrochemical stability.Electrocatalytic evaluation shows that the catalyst exhibited an excellent OER activity in 1.0 M KOH solution,i.e.,at a current density of 10 mA cm-2,the overpotential was 219 mV and the Tafel slope was only 36 mV dec-1;and the catalyst activity did not decay significantly after 100 h cycle.