Significantly Enhanced Visible-Light Photocatalytic H₂ Generation Over Semiconductor Photocatalysts Modified By Robust Transition Metal Phosphides Based Cocatalyts

At present,humans are facing more and more serious global energy crisis and hazardous environmental contamination.It is highly urgent to exploit new renewable energy and reutilize resources reasonably through green and sustainable technologies.Since the discovery of the Honda-Fujishima effect in1972,the photocatalytic hydrogen evolution by means of the artificial photosynthesis over various inorganic/organic semiconductor photocatalysts has been proven to be one of the most promising approaches to generate renewable energy,which has attracted considerable concerns for solar energy conversion to chemical fuels.However,fast recombination of photogenerated electron-hole pairs and sluggish surface hydrogen-production kinetics are two key factors limiting the photocatalytic HER over g-C3N4 nanosheets.Loading cocatalyst is one of the easiest and most effective methods to improve the separation of photogenerated electrons and holes as well as hydrogen-generation kinetics to achieve efficient photocatalytic HER activity.Although state-of-the-art Pt has been demonstrated to be an outstanding candidate,its application suffers from the disadvantages of low abundance and high price.Thus,it is of great urgency to exploit high-performance and non-noble metal/metal-free cocatalyst toward HER This paper constructed transition metal phosphides based cocatalysts in the semiconductor photocatalysts for efficient photocatalytic hydrogen evolution,which can increase light absorbance,separation efficiency of photogenerated electron-hole pairs and hydrogen-evolution active sites.The material structure and optical activity were characterized by XRD,TEM,HRTEM,EDX,BET,and DRS.Their photocatalytic properties of hydrogen were also measured.The possible mechanism was investigated by PL and electrochemical text.The results are as follows:（1）The Cu₃P was obtained by phosphating Cu（OH）₂ precursor.Then g-C₃N₄and Cu₃P were ground in an agate mortar.The max hydrogen evolution rate could reach 142.05μmolg^-1h^-1.At low content,Cu₃P serve as active sites and an electron sink to trap the photogenerated electrons and drive the photocatalytic H₂ production.At high content,we envisage that Cu3P could mainly play the semiconductor role in boosting the photocatalytic H₂evolution,which can act as a p-type semiconductor to donate electrons for g-C₃N₄ through the p-n g-C₃N₄-Cu₃P heterojunction,thus leading to the formation of competitive electron transfer on the surface of Cu₃P,due to the significantly boosted both bulk charge transport and surface reaction kinetics.（2）In this study,the metal-organic framework derived earth-abundant Co₂P cocatalysts were first served as cocatalysts to boost photocatalytic hydrogen evolution performance.the synergistic effect of Co₂P cocatalysts and the robust bioinspired environmental phosphorylation strategy in boosting photocatalyic H₂ generation over the graphitic carbon nitride nanosheets was thoroughly investigated and revealed.The max hydrogen evolution rate could reach 27.81μmolg^-1.The loaded earthabundant Co₂P nanoparticles with a good electrical conductivity could not only improve visible-light absorption and decrease the recombination of the electron-hole pairs,but also mainly serve as an efficient cocatalyst to lower the H₂-evolution overpotentials.Furthermore,K₂HPO₄ could generate an additional H₂-evolution pathway through proton-reduction cycle and enhance the oxidation ability of TEOA by effectively consuming the holes,thus significantly boosting photocatalytic hydrogen evolution of the binary g-C₃N₄-Co₂P heterojunctions（3）Efficient separation and utilization of photogenerated electrons as well as holes play decisive roles in boosting photocatalytic hydrogen evolution reaction.To reach this goal,we designed carbon black and Co_1.4Ni_0.6P as dual cocatalysts co-modified graphitic carbon nitride for efficient and stable photocatalytic HER.This resulting ternary photocatalyst was synthesized by sonochemical loading and high-temperature phosphatizing.Impressively,the maximum photocatalytic hydrogen-production rate for the ternary photocatalysts could reach 405μmolh^-1g^-1,which was 810,2 and 1.7 times higher than those of pure g-C₃N₄(0.5μmolh^-1g^-1),g C₃N4-Co_1.4Ni_0.6P(195μmolh^-1g^-1)and g-C₃N₄-1%Pt(230μmolh^-1g^-1),respectively.（4）Noble-metal-free Cu₃P-CNT H₂-evolution cocatalysts were measured by direct high-temperature phosphatizing of Cu（OH）₂-CNT.Impressively,combining the advantages of noble-metal-free Cu₃P and carbon nanotube（CNT）,the binary Cu₃P-CNT cocatalysts show high-efficiency photocatalytic H₂ evolution in Eosin Y（EY）-containing semiconductor-free photocatalytic systems.The maximum visible-light H₂-generation rate for promising EY-Cu₃P-CNT systems was 17.22 mmolg^-1h^-1.The highest apparent quantum efficiency could reach 10.23%at 500 nm.More importantly,we found that the separation of photogenerated electrons and holes in the Eosin Y,the efficiency of electron transfer from EY to the active edge sites of Cu₃P,and the electrocatalytic H₂-evolution activity of Cu₃P could be simultaneously boosted via readily adding the conductive CNT,thus achieving the significantly improved photocatalytic H₂ evolution.（5）g-C₃N₄-Co Ni Fe P were measured by direct high-temperature phosphatizing of g-C₃N₄--Co（NO₃）₂-Ni（NO₃）₂-Fe（NO₃）₂,the maximum photocatalytic hydrogen-production rate for the ternary photocatalysts could reach 1200μmolh^-1g^-1.The loaded Co Ni Fe P nanoparticles with a good electrical conductivity could not only improve visible-light absorption and decrease the recombination of the electron-hole pairs,but also mainly serve as an efficient cocatalyst to lower the H₂-evolution overpotentials.