Effect of Pd and Cu co-catalyst on the charge carrier trapping, recombination and transfer during photocatalytic hydroge
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Effect of Pd and Cu co-catalyst on the charge carrier trapping, recombination and transfer during photocatalytic hydrogen evolution over WO3– TiO2 heterojunction David Ramı´rez-Ortega1,* , Diana Guerrero-Araque2 Luis Lartundo-Rojas4, and Rodolfo Zanella1,*
, Pro´spero Acevedo-Pen˜a3
,
1
Instituto de Ciencias Aplicadas y Tecnología, Universidad Nacional Autónoma de México, Circuito Exterior S/N, Ciudad Universitaria, 04510 Mexico City, Mexico 2 CONACYT-Universidad Autónoma Metropolitana, Departamento de Química, Av. San Rafael Atlixco 156, 09340 Mexico City, Mexico 3 CONACYT-Instituto Politécnico Nacional, CICATA Legaria, 11500 Mexico City, Mexico 4 Instituto Politécnico Nacional, Centro de Nanociencias y Micro y Nanotecnología, Zacatenco, Mexico City, Mexico
Received: 4 July 2020
ABSTRACT
Accepted: 29 August 2020
Co-catalysts are well known for improving the charge carrier’s separation and transfer to species in solution, and hence, the photocatalytic hydrogen production. Thus, in this work, the effect of loading Cu and Pd species over the WO3–TiO2 structure was evaluated. The structure of WO3–TiO2 was obtained by direct hydrolysis of titanium isopropoxide (sol–gel method) in previously synthesized WO3 nanoparticles (6 mol% of WO3), forming a composite that provided direct contact between WO3 and TiO2 nanoparticles. Subsequently, 0.5 wt% of copper or 0.5 wt% of palladium loadings was deposited onto WO3– TiO2. The photocatalytic hydrogen production results show that the activity increased with the presence of Cu and Pd species, reaching hydrogen production rates of 1496 lmol g-1 h-1 and 5427.07 lmol g-1 h-1 for Cu/WT and Pd/ WT, respectively, as compared to WT structure (770.10 lmol g-1 h-1). To understand this behavior, semiconducting properties of the synthesized materials were characterized by (photo)electrochemical techniques. The presence of Cu and Pd in the structure moved the flatband position, increased the photocurrent and modified the open circuit potential under illumination toward less negative values, indicating the formation of energy states in the interface between WO3–TiO2 and the co-catalysts. These energy states at the heterojunction allow the transfer of photogenerated electrons toward co-catalysts, preventing the recombination of photogenerated charge carriers.
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Springer Science+Business
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Handling Editor: Kevin Jones.
Address correspondence to E-mail: [email protected]; [email protected]
https://doi.org/10.1007/s10853-020-05188-z
J Mater Sci
GRAPHIC ABSTRACT
Introduction Developing renewable clean energy is an approach to solve the global energy crisis, and photocatalytic production of hydrogen is considered one of them [1]. TiO2 is a semiconductor widely used in photocatalysis due to its high chemical stability, low cost and nontoxic nature [2]. However, it provides low photocatalytic efficiency due to the high recombination of photogenerated electron–hole pairs (e-–h?) [3, 4]. Therefore, coupling TiO2 with other metal oxides
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