Bifunctional noble-metal-free cocatalyst coating enabling better coupling of photocatalytic CO_(2)reduction and H_(2)O oxidation on direct Z-scheme heterojunction

Selective loading of spatially separated redox cocatalysts on direct Z-scheme heterojunctions holds great promise for advancing the efficiency of artificial photosynthesis,which however is limited to the photodeposition of noble metal cocatalysts and the fabrication of hollow double-shelled semiconductor heterojunctions.Moreover,the co-exposure of discrete cocatalyst and semiconductor increases the product diversity when both the exposed sites of which participate in CO_(2)photoreduction.Herein,we present a facile and versatile protocol to overcome these limitations via surface coating of Z-scheme heterojunctions with bifunctional noble-metal-free cocatalysts.With Cu_(2)O/Fe_(2)O_(3)(CF)as a model heterojunction and layered Ni(OH)_(2)as a model cocatalyst,it is found that Ni(OH)_(2)lying on the surfaces of Cu_(2)O and Fe_(2)O_(3)separately co-catalyzes the CO_(2)reduction and H_(2)O oxidation.Thorough experimental and theoretical investigation reveals that the Ni(OH)_(2)outer layer:(i)mitigates the charge recombination in CF and balances their transfer and consumption;(ii)reduces the rate-determining barriers for CO_(2)-to-CO and H_(2)O-to-O_(2)conversion,(iii)suppresses the side proton reduction occurring on CF,and(iv)protects the CF from component detachment.As expected,the redox reactions stoichiometrically proceed,and significantly enhanced photocatalytic activity,selectivity,and stability in CO generation are achieved by the stacked Cu_(2)O/Fe_(2)O_(3)@Ni(OH)_(2)in contrast to CF.This study demonstrates the significance of the synergy between bifunctional cocatalysts and Z-scheme heterojunctions for improving the efficacy of overall redox reactions,opening a fresh avenue for the rational design of artificial photosynthetic systems.

Millisecond-timescale electrodeposition of platinum atom-doped molybdenum oxide as an efficient electrocatalyst for hydrogen evolution reaction

We present a straightforward method for one-pot electrodeposition of platinum atoms-doped molybdenum oxide(Pt·MoO_(3-x))films and show their superior electrocatalytic activity in the hydrogen evolution reaction(HER).A~15-nm-thick Pt·MoO_(3-x) film was prepared by one-pot electrodeposition at-0.8 V for 1 ms.Due to considerably different solute concentrations,the content of Pt atoms in the electrode-posited composite electrocatalyst is low.No Pt crystals or islands were observed on the flat Pt-MoO_(3-x) films,indicating that Pt atoms were homogeneously dispersed within the MoO_(3-x) thin film.The catalytic performance and physicochemical features of Pt·MoO_(3-x) as a HER electrocatalyst were characterized.The results showed that our Pt·MoO_(3-x) film exhibits 23-and 11-times higher current density than Pt and MoO_(3-x) electrodeposited individually under the same conditions,respectively.It was found that the dramatic enhancement in the HER performance was principally due to the abundant oxygen defects.The use of the developed one-pot electrodeposition and doping method can potentially be extended to various catalytically active metal oxides or hydroxides for enhanced performance in various energy storage and conversion applications.