Engineering Heterojunctions And Utilzing Surface Plasmon Resonance Effects For Enhanced Water Electrolysis

The development and utilization of renewable energy are vital to alleviate the problems associated with the energy crisis and environmental pollution.Molecular hydrogen has attracted a lot of attention as a promising green fuel to power the globe due to its greater energy density and environmentally friendly character.The effort of investigating efficient and earth-abundant catalysts that can catalyze water splitting reactions including hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）is developing at a promising rate.In such a quest,low-cost layered catalysts and Plasmon-induced catalysts are acknowledged for their fascinating performances and strategies including heterostructuring,phase engineering,doping,etc.have been followed to develop efficient catalysts.In this thesis,Ni₅P₄-Ni₂P-NiP₂@CN catalyst was employed as a low-cost with abundant heterojunction interfaces,while Pt_x/TiN/CC and CuS@PPy-x catalysts were used as plasmon enhancement strategies for efficient electrochemical HER and OER.Firstly,the nitrogen-doped carbon-rich Ni₅P₄-Ni₂P-NiP₂@CN nanorod heterojunctions were synthesized by a simple approach.The chelated Ni（dmg）₂ was synthesized by using Ni²⁺and dimethylglyoxal dioxime（dmg）.Then,using Ni（dmg）₂as a template,the three-phase heterogeneous structured Ni₅P₄-Ni₂P-NiP₂@CN catalyst was successfully synthesized through calcination at 800°C for 3 h followed by phosphating at 600°C for 3 h.The heterostructured Ni₅P₄-Ni₂P-NiP₂@CN catalyst enabled boosting the catalytic performance due to the;1)enriched interfaces,2)enhanced active sites,and 3)high crystalline nitrogen-doped carbon at the external layers.According to the electrochemical measurements,only 106 and 150 m V overpotentials are required to provide a current density of 10 m A cm^-2 with Tafel slopes of 57.5 and 97.4 m V dec^-1 in 0.5 M H₂SO₄ and 1.0 M KOH,respectively.Likewise,the Ni₅P₄-Ni₂P-NiP₂@CN heterostructure also exhibited excellent electrocatalytic oxygen evolution performance.It needs about 410 m V overpotential to offer a current density of 100 m A cm^-2with a Tafel slope of 23.5 m V dec^-1 in 1.0 M KOH.Remarkably,the as-prepared heterojunction operates for a long-term OER.Therefore,a bifunctional catalyst for efficient overall water splitting was developed through heterojunction interface engineering.Secondly,the TiN/CC was successfully synthesized by converting the TiO₂nanowires（TiO₂/CC）by calcination under an NH₃ atmosphere for 3 h at 900 ^oC without altering the morphology.Then,the Pt nanoparticles were uniformly and controllably deposited on the surface of the TiN/CC nanowires by electrochemical deposition to prepare the plasmonic Pt_x/TiN/CC（x=500,750,1000,and 1500 cycle scans）for HER.The as-prepared Pt_x/TiN/CC electrodes unveiled excellent light-enhanced HER performance.Of the as-prepared catalysts,the Pt₁₀₀₀TiN/CC electrode demonstrated a significant electrocatalytic enhancement with overpotential of 16 m V at a current density of 10 m A cm^-2 for HER induced by the surface plasmon resonance accompanied by efficient electron transfer to the Pt co-catalyst,outperformed the commercial 20%Pt/C catalyst.It provides a new insight into the development of non-noble plasmonic electrocatalysts for HER and beyond.Thirdly,the polypyrrole（PPy）was deposited on the surface of CuS by the electrochemical deposition method.The PPy has the advantages of excellent light absorption performance and greater OER co-catalysis nature.As a result,the close-contact interface formed between PPy and CuS greatly improves the light absorbance,which increases the photogenerated electron-hole separation rate upon light illumination,thus boosting the OER.The overpotentials of 295 m V and 333 m V were recorded at the current densities of 10 and 100 m A cm^-2,respectively;with about 17m V dec^-1 Tafel slope under light irradiation.The CuS@PPy nanocomposites demonstrated greater stability with continuous improvement of OER for 24 h under light illumination in 1.0 M KOH than the bare CuS electrode.Therefore,the deposition of PPy over CuS can surge the electrocatalytic activity of OER and improve long-term electrolysis.