Effect of the Valence State in Co-Based Cocatalyst on the Photocatalytic Oxygen Evolution Reactivity of WO₃

Abstract

WO3 is one of the most promising photocatalysts with a suitable energy band structure for water oxidation; however, the quick recombination of photoinduced charge carriers seriously limits the photocatalytic efficiency. Loading of suitable cocatalysts is considered as an effective method to significantly improve the photocatalytic activity. Herein, we used a facile one-step hydrothermal method and a “hydrothermal + photodeposition” method to synthesize xCo3O4/WO3 (x = 0.2, 0.4, 0.8) and yCoOOH/WO3 (y = 2, 3, 4), respectively. We found that, in comparison with the pristine WO3, both xCo3O4/WO3 and yCoOOH/WO3 exhibited remarkably increased photocatalytic O2 evolution activities owing to the loading of two Co-based cocatalysts Co3O4 and CoOOH, respectively. Moreover, the optimal O2 evolution rate achieved over 0.4Co3O4/WO3 (194 μmol·h–1) was ∼2.1 times that over 3CoOOH/WO3 (94 μmol·h–1). The superior photocatalytic O2 evolution activity of Co3O4/WO3 over CoOOH/WO3 could be attributed to the mixed valences of Co2+ and Co3+ in Co3O4, which was more favorable than CoOOH with the sole valence of Co3+ for promoting the separation and transfer of photoinduced electrons and holes. This work suggests a promising way to the development of noble-metal-free cocatalyst by using transition-metal oxide with mixed valence states for efficient photocatalytic water oxidation.

Infrared Absorption of Zn0.5Cd0.5S Photocatalyst Bandgap-Excited Under an Aqueous Environment

“…In general, certain classes of photocatalytic materials have their “preferred” scavenging solution where the resultant product yields are maximized due to the excellent scavenging abilities of the respective solutions. For example, thioacetamide (TEOA) as the best-in-slot (BIS) hole scavenger for the g-C 3 N 4 polymeric photocatalyst, − Na 2 S/Na 2 SO 3 or AA as the BIS hole scavenger for sulfide-based photocatalysts in which one may provide better outcome over another depending on the cocatalysts used, − Na 2 S 2 O 8 as an electron scavenger for ferrites such as NiFeO x and BiFeO 3 , , and AgNO 3 or FeCl 3 as the more generic go-to electron scavenger in many of the studies using the popular oxygen evolution photocatalysts, WO 3 and BiVO 4 . − As the use of ZCS for oxygen evolution is rather scarce, the combination of ZCS and FeCl 3 as the photocatalyst–electron scavenger pair has most likely not been assessed before. Considering the occasion where FeCl 3 has great synergy with ZCS and can effectively draw away the photoexcited electrons in ZCS, this will leave a substantial amount of holes in the valence band (VB) of ZCS that can thus contribute to strong electronic absorption during ATR-FTIR assessment as evidently portrayed in Figure a,c.…”

Synergistic Bimetallic Sites in 2D-on-2D Heterostructures for Enhanced C–N Coupling in Sustainable Urea Synthesis

“…In Figure 2(i), the SAED pattern is clearly visible as monoclinic phases are formed in accordance with the crystal plane (002). 49 As can be seen in Figure 3 39,48 An X-ray photoelectron spectrometer (XPS) was used to determine the chemical structure and binding state of the Ru− Pd/WO 3 /MXene nanocatalysts. As can be seen in Figure 4 (a), the survey spectrum of Ru−Pd/WO 3 /MXene reveals the presence of Ti, W, Ru, Pd, N, C, and O elements.…”

2022 Pioneers in Energy Research: Jinhua Ye

“…Wu’s group summarized the common synthesis methodologies of metal oxide aerogels and their photocatalytic applications in water treatment, solar water splitting, and gas-chase reactions, including CO 2 reduction and CO oxidation . Wang and his co-workers employed Co 3 O 4 and CoOOH as the co-catalysts of WO 3 for photocatalytic O 2 production . It is revealed that the mixed valence of co-catalysts is more favorable for photocatalytic water oxidation.…”

“…25 Wang and his co-workers employed Co 3 O 4 and CoOOH as the co-catalysts of WO 3 for photocatalytic O 2 production. 26 It is revealed that the mixed valence of co-catalysts is more favorable for photocatalytic water oxidation. Zhang's group presented serpentine Ni 3 Ge 2 O 5 (OH) 4 nanosheets on porous Mo 2 N for an efficient oxygen evolution reaction.…”