Homogeneous And Heterogeneous Catalysts Containing Low Cost Transition Metals To Drive Photocatalytic Water Splitting

The artificial photosynthesis process can covert solar energy into chemical energy to help store the energy,in which photocatalytic water splitting is an attracting method to get green and sustainable hydrogen energy to replace conventional fossil energy,solve energy and environment problems.Due to the complicated four protons and electrons within oxygen evolution process,the half reaction-water oxidation becomes the bottleneck for overall water splitting.Thus,exploring robust and efficient water oxidation catalysts is very important nowadays.The catalysts that range from homogeneous materials to heterogeneous materials can be controlled to obtain the highly effective water oxidation activity with the optimal condition.First of all,the polyoxomeatalates?POMs?with all-inorganic ligands based on low cost transition metals own the ability to resist oxidation environment,so that we use the POMs as homogeneous catalysts to achieve effective water oxidation activity.Besides,the nanomaterials containing transition metal oxides or sulfides can be selected as candidates to obtain the high activity for oxygen evolution.However,the homogeneous catalysts are hard to recycle,and the heterogeneous materials have shortcomings that the mechanism is not very easy to analyze within water oxidation process.Therefore,the heterogenization is a potential way to make full use of the homogeneous materials and heterogeneous materials.Based on above opinions,there experiments are carried out in the following:1.The rationally obtained 3D hierarchical cobalt sulfides are acted as robust bifunctional photocatalysts to achieve high activity for visible-light-driven water splitting,exhibiting H₂ evolution rate of 1196?mol h^-1 g^-1 and O₂ yield of 63.5%.For water oxidation,the dramatic decline of[Ru?bpy?₃]³⁺concentration confirms that effective electron transfers between the photosensitizer and catalyst CoS-2.For HER,transient absorption experiments verify that a rapid electron transfers from excited³EY*to the catalyst Co S-2.This work gives the direction for design water splitting catalysts based on efficient,earth-abundant,and non-noble materials that functionally mimic photosystem I and photosystem II.2.Inorganic molecular tetrairon???-substituted polyoxotungstate [Fe₄^??H₂O?₂(P₂W₁₅O₅₆)₂]^12-?Fe₄POM?is used to catalyze visible-light-driven oxygen evolution,which displays excellent catalytic activity(oxygen evolution yield of 48%,TOF_catalyst of 5 s^-1,TON_catalyst of 900 and?_QY yield of 24%)in a homogeneous system.And Fe₄POM is anchored on the surface of SBA-15 by electrostatic interaction,exhibiting oxygen evolution yield of 12%.The electrostatic interaction is rationally designed as solid connection between??3-aminopropyl?triethoxysilane?apts-modified mesoporous SBA-15 and polyoxoanion.Through ³¹P MAS NMR,XPS and ICP-AES analyses,molecule is confirmed to be intact when anchored in heterogeneous system,and SBA-15-apts-Fe₄POM composite maintains good stability after the photocatalytic reaction.3.A photocatalytic water oxidation system is fabricated using decahedron shaped BiVO₄ as light-harvesting material and an effective eleven iron-containing polyoxometalate Na₂₇[Fe₁₁?H₂O?₁₄?OH?₂(W₃O₁₀)₂(?-SbW₉O₃₃)₆](Fe₁₁POM)as cocatalyst to overcome sluggish water oxidation kinetics,which achieves almost 10times photoactivity enhancement?O₂ yield of 39.1%?than that of pure BiVO₄.After lots of characterizations,we figure out that Fe O_x decomposed from Fe₁₁POM is the true cocatalyst in photocatalytic water oxidation system.The close connection between in-situ selectively photo-deposited nanofim and 110 facet of BiVO₄ is clearly observed,which efficiently improves the photocatalytic water oxidation activity.