In order to avoid the formation ofηphase(W_(6)Co_(6)C or W_(3)Co_(3)C)that adversely affects the sintering process and its products in the preparation process of ultra-fine WC-Co powder,a technical route of prereduct...In order to avoid the formation ofηphase(W_(6)Co_(6)C or W_(3)Co_(3)C)that adversely affects the sintering process and its products in the preparation process of ultra-fine WC-Co powder,a technical route of prereduction of WO_(3)-Co_(3)O_(4)to WO_(2)-Co and then deep reduction carbonization to WC-Co powder has been proposed.This study mainly investigates the influence of gas partial pressure on the pre-reduction process of WO_(3)-Co_(3)O_(4)under a mixed atmosphere of H_(2)-C_(2)H_(4)-Ar at 600℃and establishes the kinetic equations of pre-reduction and carbon evolution.The results indicate that increasing the partial pressure of hydrogen is conducive to the rapid and complete conversion of WO_(3) to WO_(2).High carbon content can be generated by the deposition of C_(2)H_(4),and it hinders the diffusion of the reducing gas;WO_(3)still cannot be completely reduced to WO_(2)as the partial pressure of C_(2)H_(4) increases to 60%.For the carbon evolution of C_(2)H_(4),the carbon amount is positively related to the H_(2)partial pressure,but it shows the highest amount and evolution rate when the ethylene partial pressure is 20%.Based on the reduction rate curves of WO_(3) and carbon evolution rate curves of C_(2)H_(4),the rate equations of pre-reduction and carbon evolution of WO_(3)-Co_(3)O_(4)system at 600℃are established.The pre-reduction reaction belongs to the first-order reaction,and its equation is expressed as follows:r=-(dw_(WO_(3)))/dt=(9±0.15)×10^(-2)×P_(H_(2))^(0.44)P_(C_(2)H_(4))&(0.57)The carbon deposition rate equation of C_(2)H_(4) can be expressed as follows:r=-(dc_C)/dt=r_f-r_b≌7.35×10^(-2)×P_(C_(2)H_(4))^(0.31)展开更多
As one of the most promising photoanode candidates for photoelectrochemical(PEC)water splitting,the photocurrent density of BiVO_(4) still needs to be further improved in order to meet the practical application.In thi...As one of the most promising photoanode candidates for photoelectrochemical(PEC)water splitting,the photocurrent density of BiVO_(4) still needs to be further improved in order to meet the practical application.In this work,a highly‐matched BiVO_(4)/WO_(3) nanobowl(NB)photoanode was constructed to enhance charge separation at the interface of the junction.Upon further modification of the BiVO_(4)/WO_(3)NB surface by NiOOH/FeOOH as an oxygen evolution cocatalyst(OEC)layer,a high photocurrent density of 3.05 mA cm^(−2) at 1.23 V vs.RHE has been achieved,which is about 5‐fold higher than pristine BiVO_(4) in neutral medium under AM 1.5 G illumination.5 times higher IPCE at 450 nm is also achieved compared with the BiVO_(4) photoanode,leading to about 95%faradaic efficiency for both H_(2) and O_(2) gas production.Systematic studies attribute the significantly enhanced PEC performance to the smaller BiVO_(4) particle size(<90 nm)than its hole diffusion length(~100 nm),the improved charge separation of BiVO_(4) by the single layer WO_(3) nanobowl array and the function of OEC layers.Such WO_(3)NB possesses much smaller interface resistance with the substrate FTO glass and larger contact area with BiVO_(4) nanoparticles.This approach provides new insights to design and fabricate BiVO_(4)‐based heterojunction photoanode for higher PEC water splitting performance.展开更多
基金the National Natural Science Foundation of China(22078326,21878305,21908227)。
文摘In order to avoid the formation ofηphase(W_(6)Co_(6)C or W_(3)Co_(3)C)that adversely affects the sintering process and its products in the preparation process of ultra-fine WC-Co powder,a technical route of prereduction of WO_(3)-Co_(3)O_(4)to WO_(2)-Co and then deep reduction carbonization to WC-Co powder has been proposed.This study mainly investigates the influence of gas partial pressure on the pre-reduction process of WO_(3)-Co_(3)O_(4)under a mixed atmosphere of H_(2)-C_(2)H_(4)-Ar at 600℃and establishes the kinetic equations of pre-reduction and carbon evolution.The results indicate that increasing the partial pressure of hydrogen is conducive to the rapid and complete conversion of WO_(3) to WO_(2).High carbon content can be generated by the deposition of C_(2)H_(4),and it hinders the diffusion of the reducing gas;WO_(3)still cannot be completely reduced to WO_(2)as the partial pressure of C_(2)H_(4) increases to 60%.For the carbon evolution of C_(2)H_(4),the carbon amount is positively related to the H_(2)partial pressure,but it shows the highest amount and evolution rate when the ethylene partial pressure is 20%.Based on the reduction rate curves of WO_(3) and carbon evolution rate curves of C_(2)H_(4),the rate equations of pre-reduction and carbon evolution of WO_(3)-Co_(3)O_(4)system at 600℃are established.The pre-reduction reaction belongs to the first-order reaction,and its equation is expressed as follows:r=-(dw_(WO_(3)))/dt=(9±0.15)×10^(-2)×P_(H_(2))^(0.44)P_(C_(2)H_(4))&(0.57)The carbon deposition rate equation of C_(2)H_(4) can be expressed as follows:r=-(dc_C)/dt=r_f-r_b≌7.35×10^(-2)×P_(C_(2)H_(4))^(0.31)
文摘As one of the most promising photoanode candidates for photoelectrochemical(PEC)water splitting,the photocurrent density of BiVO_(4) still needs to be further improved in order to meet the practical application.In this work,a highly‐matched BiVO_(4)/WO_(3) nanobowl(NB)photoanode was constructed to enhance charge separation at the interface of the junction.Upon further modification of the BiVO_(4)/WO_(3)NB surface by NiOOH/FeOOH as an oxygen evolution cocatalyst(OEC)layer,a high photocurrent density of 3.05 mA cm^(−2) at 1.23 V vs.RHE has been achieved,which is about 5‐fold higher than pristine BiVO_(4) in neutral medium under AM 1.5 G illumination.5 times higher IPCE at 450 nm is also achieved compared with the BiVO_(4) photoanode,leading to about 95%faradaic efficiency for both H_(2) and O_(2) gas production.Systematic studies attribute the significantly enhanced PEC performance to the smaller BiVO_(4) particle size(<90 nm)than its hole diffusion length(~100 nm),the improved charge separation of BiVO_(4) by the single layer WO_(3) nanobowl array and the function of OEC layers.Such WO_(3)NB possesses much smaller interface resistance with the substrate FTO glass and larger contact area with BiVO_(4) nanoparticles.This approach provides new insights to design and fabricate BiVO_(4)‐based heterojunction photoanode for higher PEC water splitting performance.
