A low-valent cobalt oxide co-catalyst to boost photocatalytic water oxidation via enhanced hole-capturing ability

Abstract

Ultrafine and well-dispersed CoOx co-catalysts with a dominating ratio of Co2+ provide more attractive sites as well as stronger attraction forces for photogenerated holes, which can greatly enhance photocatalytic water oxidation efficiency.

Development and Functionalization of Visible-Light-Driven Water-Splitting Photocatalysts

“…Therefore, these properties need to be considered when improving the functionality of the photocatalyst by modifying the cocatalyst. This section discusses six approaches to improving such cocatalysts, as follows: (i) particle-size control ( Section 3.1 ; Figure 17 A) [ 73 , 74 , 75 , 77 , 218 ]; (ii) chemical composition control ( Section 3.2 ; Figure 17 B) [ 76 , 219 , 220 ]; (iii) morphology control ( Section 3.3 ; Figure 17 C) [ 221 , 222 , 223 , 224 ]; (iv) interface structure control ( Section 3.4 ; Figure 17 D) [ 225 ]; (v) surface-structure control ( Section 3.5 ; Figure 17 E) [ 77 , 226 , 227 , 228 , 229 , 230 , 231 , 232 , 233 , 234 , 235 , 236 , 237 , 238 , 239 , 240 , 241 ]; and (vi) charge-state control ( Section 3.6 ; Figure 17 F) [ 242 , 243 ]. For the semiconductor photocatalysts described in this section, the appropriate cocatalysts, possible reactions (OWSR, HER, or OER;…”

“…Similar results have been reported by Liu, Yang, and co-workers. In 2021, these authors successfully loaded Co 2+ -based CoO x cocatalysts (~2.5 nm) or Co 3+ -based CoO x cocatalysts (~2.6 nm) on TaON photocatalysts using a photochemical metal–organic deposition (PMOD) method [ 243 ]. Photocatalytic studies showed that Co 2+ -based CoO x cocatalysts were 1.6 times more effective for OER than Co 3+ -based CoO x cocatalysts and that TaON loaded with Co 2+ -based CoO x cocatalysts had an AQY of 21.2% (at 420 ± 15 nm; Figure 32 A and Table 3 ).…”

“…( B ) Proposed mechanism of the photocatalytic water-oxidation process of CoO x NPs/TaON, indicating accelerated hole transportation and reaction on the Co 2+ species. Reproduced with permission from reference [ 243 ]. Copyright 2021 The Royal Society of Chemistry.…”

Transition‐Metal‐Based Cocatalysts for Photocatalytic Water Splitting

“…Transition metal oxides involving the cobalt oxide, [ 48,355,356,358–361,363–365,381 ] manganese oxide, [ 49,366,381a,382 ] chromium oxide, [ 357,383 ] molybdenum oxide, [ 384 ] nickel oxide, [381a,382b] iron oxide, [ 362,381a ] copper oxide, [381a] lead oxide, [382b] and several bimetal oxides [ 367–370,385 ] have been investigated as active cocatalysts to collect photoinduced holes for O 2 production in photocatalytic water splitting. The deposition of these cocatalysts is usually achieved based on the impregnation, hydrothermal, and photodeposition methods.…”

“…They found that coating a magnesia nanolayer on the surface of Ta 3 N 5 could greatly improve its interface contact with CoO x cocatalysts, leading to an enhancement of up to 23 times in O 2 evolution rate in contrast to that of pristine Ta 3 N 5 and a high AQE value of 11.3% under 500–600 nm light illumination. The work by Yang et al [ 365 ] showed that ultrafine CoO x cocatalysts with controllable valence states (Co 2+ and Co 3+ ) were fabricated on the TaON surface. The resultant Co 2+ dominated CoO x loaded TaON exhibited a higher photocatalytic O 2 evolution efficiency because more attractive sites and stronger attraction forces for photogenerated holes were provided.…”