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 μmol g−1 h−1 and 5427.07 μmol g−1 h−1 for Cu/WT and Pd/WT, respectively, as compared to WT structure (770.10 μmol 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.

中文翻译：

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Pd和Cu助催化剂对WO3-TiO2异质结光催化析氢过程中载流子捕获、复合和转移的影响

众所周知，助催化剂可以改善电荷载流子的分离和向溶液中物质的转移，从而改善光催化制氢。因此，在这项工作中，评估了负载 Cu 和 Pd 物种对 WO3-TiO2 结构的影响。WO3-TiO2 的结构是通过在先前合成的 WO3 纳米颗粒（WO3 的 6 mol%）中直接水解异丙醇钛（溶胶-凝胶法）获得的，形成复合材料，使 WO3 和 TiO2 纳米颗粒直接接触。随后，将 0.5 wt% 的铜或 0.5 wt% 的钯负载沉积到 WO3-TiO2 上。光催化产氢结果表明，随着Cu和Pd物种的存在，活性增加，Cu/WT和Pd/WT的产氢速率分别达到1496 μmol g-1 h-1和5427.07 μmol g-1 h-1，分别，与 WT 结构（770.10 μmol g-1 h-1）相比。为了理解这种行为，合成材料的半导体特性通过（光）电化学技术进行了表征。结构中Cu和Pd的存在移动了平带位置，增加了光电流并将光照下的开路电位修改为较小的负值，表明在WO3-TiO2和助催化剂之间的界面中形成了能态。异质结处的这些能态允许光生电子向助催化剂转移，防止光生电荷载流子的复合。结构中Cu和Pd的存在移动了平带位置，增加了光电流并将光照下的开路电位修改为较小的负值，表明在WO3-TiO2和助催化剂之间的界面中形成了能态。异质结处的这些能态允许光生电子向助催化剂转移，防止光生电荷载流子的复合。结构中Cu和Pd的存在移动了平带位置，增加了光电流并将光照下的开路电位修改为较小的负值，表明在WO3-TiO2和助催化剂之间的界面中形成了能态。异质结处的这些能态允许光生电子向助催化剂转移，防止光生电荷载流子的复合。