Phosphorous Incorporated Carbon Encapsulated Transition Metal Compounds Toward Water Electrolysis

Hydrogen energy with high energy density is a promising candidate to construct sustainable energy system,its large-scale application is an effective way to alleviate fossil energy crisis and environmental pollution.Water electrolysis is an environmentally friendly technology to sustainably provide hydrogen with high purity.To date,prodigious progress has been made on the exploring of earth abundant transition metal based catalysts.For example,phosphides?TMPs?and alloys?TMAs?have been emerging as efficient electrocatalysts for hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?.Besides,graphitic carbon?GC,especially heteroatoms with different electronegativity doped carbon?substrate and encapsulation will significantly improve both the activity and the stability.In the dissertation,making use of the highly active TMPs and TMAs,and robust GC with high conductivity,we employed innovative approach and prepared P incorporated GC encapsulated transition metal compounds.The main research contents are as follows:?1?Take advantage of the phosphorous biomass,phytic acid?PA?,we successfully synthesize a series of bi-functional TMPs.In 0.5 M H₂SO₄,Ni₂P/C and Co_xP/C needs 153mV and 175 mV to obtain 10 mA cm^-2 toward HER,respectively.And in 1.0 M KOH,the overpotentials to reach the same hydrogen evolution current density are 250 mV and 272mV for Ni₂P/C and Co_x P/C,respectively.Furtherly,when catalyzing OER,Ni₂P/C and Co_xP/C requires 339 mV and 302 mV to drive 10 mA cm^-2,respectively.This work provides a facile method to prepare TMPs,which may extend to various TMPs with large scale,and bring hopes to the application to more energy conversion related electrocatalysis.?2?We report a catalyst composing Ni₂P nanoparticles encapsulated by ultrathin phosphorous-doped GC on the graphene network.Benefiting from the unique architecture,this hybrid catalyst needs only 110 mV and 150 mV to reach 10 mA cm^-2 in 0.5M H₂SO₄and 1.0 M KOH toward HER for more than 24 hours,respectively.Theoretical analysis reveals the strong electronic interactions between ultrathin GC and Ni₂P core,P dopant and neighboring C on the shell are responsible for the enhanced electrochemical activity.This work offers not only an effective method to prepare the efficient core-shell catalysts but also valuable understandings and insights for future design of core-shell structures through the electronic modulation to enhance the activity and stability of catalysts.?3?We employ a weak electrochemical activation protocol?-0.3⁰.5 V vs.RHE?to investigate the surface evolution of NiFeP@rGO.The as-formed oxygen-abundant FePi/NiFeP synergy contributes to the enhanced catalytic activity,which requires merely210 mV and 270 mV to achieve 10 mA cm^-2 and 100 mA cm^-2 in 1.0 M KOH,respectively,surpass the commercial IrO₂.Further analysis reveal the pivotal role of the interaction between Ni and Fe,as well as the optimized Fe content,in facilitating the formation of FePi/NiFeP synergy.This work provides new evidences on the surface evolution of TMPs for efficient water oxidation.Therefore,the understandings on pre-catalysts may inspire more rational design strategies for efficient electrocatalysts.?4?We report the N,P co-doped ultrathin GC encapsulating CoNi alloy with ultra-small size.The as-prepared CoNi@NPC show remarkable performance toward both HER and OER in 1.0 M KOH,which needs only 48 mV and 260 mV to obtain current density of 10 mA cm^-2,respectively.When coupled as two electrode configuration cell,the cell outputs 10 mA cm^-2 of merely 1.53 V,outperforms the state-of-the-art catalysts Pt/C?IrO₂.This work reveals the role of moderate P-doping and synergistic effect between N and P in enhanced performance.Therefore,it will offer important understandings on heteroatoms doped GC encapsulated catalysts and may inspire more rational design strategies for efficient electrocatalysts.