Self-improvement of solar water oxidation for the continuously-irradiated hematite photoanode

Integration of a Cu2O/ZnO heterojunction and Ag@SiO2 into a photoanode for enhanced solar water oxidation

Photoelectrochemical water splitting (PEC-WS) has attracted considerable attention owing to its low energy consumption and sustainable nature. Constructing semiconductor heterojunctions with controllable band structure can effectively facilitate photogenerated carrier separation. In this study, a FTO/ZnO/Cu2O/Ag@SiO2 photoanode with a Cu2O/ZnO p-n heterojunction and Ag@SiO2 nanoparticles is constructed to investigate its PEC-WS performance. Compared with a bare ZnO photoanode, the photocurrent density of the FTO/ZnO/Cu2O/Ag@SiO2 photoanode (0.77 mA cm-2) at 1.23 VRHE exhibits an increment of 88%, and a cathodic shift of 0.1 V for the on-set potential (0.4 VRHE). Detailed photoelectrochemical analyses reveal that the Cu2O/ZnO p-n heterojunction formed between Cu2O and ZnO can effectively promote photogenerated carrier separation. The surface plasmonic effect of the Ag@SiO2 nanoparticles can further promote the photogenerated carrier transfer efficiency, which synergistically improves the PEC-WS performance.

Regulating a Zn/Co bimetallic catalyst in a metal-organic framework and oxyhydroxide for improved photoelectrochemical water oxidation

As one of the most popular photoanode materials, hematite (α-Fe2O3) has obvious advantages in the field of photoelectrochemical water splitting (PEC-WS). However, it is difficult to achieve excellent PEC-WS performance without loading a cocatalyst serving as an electron/hole collector to promote photogenerated carrier separation. In this work, FTO/Sn@α-Fe2O3 photoanodes are modified with ZnCo-ZIF and ZnCoOOH bimetallic catalysts to obtain FTO/Sn@α-Fe2O3/Zn0.5Co0.5-ZIF and FTO/Sn@α-Fe2O3/Zn0.46Co0.54OOH photoanodes. Their photocurrent densities reach 2.6 mA cm-2 and 2.3 mA cm-2 at 1.23 VRHE, respectively. The detailed mechanism studies demonstrate that both ZnCoOOH and ZnCo-ZIF can effectively decrease the transfer resistance, increase the Fe2+/Fe3+ ratio and reduce the charge recombination of the α-Fe2O3 film, which synergistically improves the PEC-WS performance. Compared with ZnCoOOH, the ZnCo-ZIF exhibits better photogenerated carrier transfer efficiency and catalytic performance, which mainly can be attributed to the improved binding energy between the ZnCo-ZIF catalyst and the α-Fe2O3 film. This work provides a simple and feasible strategy for constructing bimetallic catalysts and deepens the understanding of different types of bimetallic catalysts for high-performance PEC-WS systems.

Photoelectrochemical properties of single-grain hematite films grown by electric-field-assisted liquid phase deposition

This article reports a modification of the conventional liquid phase deposition (C-LPD) method for the single-grain deposition of α-Fe2O3 (hematite) films into an electric-field-assisted liquid phase deposition (EA-LPD).

Underlayer engineering into the Sn-doped hematite photoanode for facilitating carrier extraction

A semiconductor underlayer(s) has been extensively used to improve the performance of photoelectrochemical (PEC) cells. Unfortunately, in many cases, the incorporation of underlayers leads to degraded system performances. A comprehensive study on the functions and manipulations of underlayers is therefore of high significance for achieving high-performance PEC cells. This study indicates that Sn-doped hematite photoanodes decorated with various underlayer materials show substantially distinguished photocurrent responses, leading to qualitatively different PEC cells. With an optimized TiO2 (ITO, Al2O3) underlayer, the photocurrent density at 1.23 V versus RHE can be enhanced from 0.25 to 0.71 (0.59, 0.42) mA cm-2, while it is decreased to 0.14 mA cm-2 by using NiO. Our further analysis reveals that the performance differences come mainly from the distinguished bulk and surface carrier recombination effects, i.e., (1) metal doping (i.e., Ti4+, In3+ and Al3+) from the underlayers improves the conductivity of hematite film and thus reduces the bulk recombination; (2) the underlayers of TiO2, ITO and Al2O3 can effectively suppress the carrier recombination at the bottom/top surfaces of the hematite layer, while the NiO underlayer leads to a higher surface recombination. Our work provides a basis for selecting an underlayer and a general guideline for the interface engineering for high performance photoelectrodes.