Photo-induced Au–Pd alloying at TiO <sub>2</sub> {101} facets enables robust CO <sub>2</sub> photocatalytic reduction into hydrocarbon fuels

Author(s): Qian Chen ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Xianjie Chen ¹ ^, ⁶ ^, ⁷ ^, ⁵ , Minling Fang ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Jiayu Chen ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Yongjian Li ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Zhaoxiong Xie ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Qin Kuang ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Lansun Zheng ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵

Publication date (Electronic): 2019

Journal: Journal of Materials Chemistry A

Publisher: Royal Society of Chemistry (RSC)

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Abstract

Au–Pd alloy catalytic sites were specifically constructed on anatase TiO ₂ {101} facets for promoting CO ₂ conversion to hydrocarbons.

Abstract

While photocatalytic conversion of CO ₂ is a promising approach for the production of renewable fuels, it has always suffered from low yield and poor selectivity, thus the artful design of catalytic sites holds the key to addressing this issue. Herein, we construct Au–Pd alloy catalytic sites on TiO ₂ {101} facets for robust CO ₂ conversion to hydrocarbons through a photo-induced alloying strategy. The Au–Pd alloy provides abundant sites for CO ₂ adsorption and activation, in which the uniformly dispersed Pd atoms could synchronously act as hydrogenation centers. The synergistic effect of Au and Pd, in combination with the photogenerated electron-rich nature of TiO ₂ {101} facets, is proposed to account for the highly efficient CO ₂ reduction. Remarkably, the optimal sample has achieved a high selectivity of 85% (71%: CH ₄, 14%: C ₂H ₄ and C ₂H ₆) for hydrocarbons with an evolution rate of 14.3 μmol g ⁻¹ h ⁻¹. This work provides new insights into the design of active sites for CO ₂ photoreduction, and highlights the significance of surface structure engineering in improving selectivity towards high grade carbon products.

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Roles of cocatalysts in photocatalysis and photoelectrocatalysis.

Jinhui Yang, Donge Wang, Hongxian Han … (2013)

Since the 1970s, splitting water using solar energy has been a focus of great attention as a possible means for converting solar energy to chemical energy in the form of clean and renewable hydrogen fuel. Approaches to solar water splitting include photocatalytic water splitting with homogeneous or heterogeneous photocatalysts, photoelectrochemical or photoelectrocatalytic (PEC) water splitting with a PEC cell, and electrolysis of water with photovoltaic cells coupled to electrocatalysts. Though many materials are capable of photocatalytically producing hydrogen and/or oxygen, the overall energy conversion efficiency is still low and far from practical application. This is mainly due to the fact that the three crucial steps for the water splitting reaction: solar light harvesting, charge separation and transportation, and the catalytic reduction and oxidation reactions, are not efficient enough or simultaneously. Water splitting is a thermodynamically uphill reaction, requiring transfer of multiple electrons, making it one of the most challenging reactions in chemistry. This Account describes the important roles of cocatalysts in photocatalytic and PEC water splitting reactions. For semiconductor-based photocatalytic and PEC systems, we show that loading proper cocatalysts, especially dual cocatalysts for reduction and oxidation, on semiconductors (as light harvesters) can significantly enhance the activities of photocatalytic and PEC water splitting reactions. Loading oxidation and/or reduction cocatalysts on semiconductors can facilitate oxidation and reduction reactions by providing the active sites/reaction sites while suppressing the charge recombination and reverse reactions. In a PEC water splitting system, the water oxidation and reduction reactions occur at opposite electrodes, so cocatalysts loaded on the electrode materials mainly act as active sites/reaction sites spatially separated as natural photosynthesis does. In both cases, the nature of the loaded cocatalysts and their interaction with the semiconductor through the interface/junction are important. The cocatalyst can provide trapping sites for the photogenerated charges and promote the charge separation, thus enhancing the quantum efficiency; the cocatalysts could improve the photostability of the catalysts by timely consuming of the photogenerated charges, particularly the holes; most importantly, the cocatalysts catalyze the reactions by lowering the activation energy. Our research shows that loading suitable dual cocatalysts on semiconductors can significantly increase the photocatalytic activities of hydrogen and oxygen evolution reactions, and even make the overall water splitting reaction possible. All of these findings suggest that dual cocatalysts are necessary for developing highly efficient photocatalysts for water splitting reactions.