High-entropy oxynitride as a low-bandgap and stable photocatalyst for hydrogen production

Abstract

Metal oxynitrides are promising photocatalysts due to their narrow bandgap, but their lower stability compared to metal oxides is a drawback. The introduction of high-entropy alloys with entropy-stabilization features has...

High-Pressure Torsion for Synthesis of High-Entropy Alloys

“…Metals 2021, 11, x FOR PEER REVIEW 3 of 14 such as high-entropy hydride MgTiVCrFe-H for hydrogen storage [75], high-entropy oxide TiZrHfNbTaO11 for photocatalytic hydrogen production [76] and high-entropy oxynitride TiZrHfNbTaO6N3 as a photocatalyst with large light absorbance [77].…”

“…Large light absorption, long electron/hole recombination time and high chemical stability are some parameters that are important in designing new photocatalysts [99,100]. High-entropy photocatalysts are one of the newest family of photocatalysts developed recently for hydrogen production [76,77].…”

“…To develop oxynitrides with low bandgap and high stability for photocatalytic application, Edalati et al [77] synthesized a high-entropy oxynitride based on the mixture of Ti, Zr, Hf, Nb and Ta cations, which can generate a d 0 electronic configuration that is appropriate for photocatalytic activity [101,102]. They developed a three-step synthesis technique: (i) mechanical alloying of elemental powders by HPT processing for 100 turns to produce a BCC TiZrHfNbTa alloy; (ii) oxidation of the BCC alloy at 1373 K for 24 h to produce TiZrHfNbTaO 11 oxide; (iii) nitriding the oxide in ammonia at 1373 K for 7 h to produce an oxynitride.…”

“…Furthermore, the light absorbance of this oxynitride was better than all binary oxides formed in the Ti-Zr-Hf-Nb-Ta system as well the corresponding high-entropy oxide, as shown in Figure 8. This high-entropy oxynitride with high chemical stability could produce hydrogen from photocatalytic water splitting, introducing high-entropy oxynitrides as new low-bandgap and stable photocatalysts [77].…”

“…More recently, the HPT method was used to impart ultra-SPD and synthesize CoCrFeMnNi with high hardness [64]. Since the concept of HEAs has been extended to non-metallic materials such as oxides [65,66], nitrides [67,68], carbides [69,70], borides [71,72] and ceramics [73,74], there have been some attempts to use the HPT method to synthesize non-metallic HEAs such as high-entropy hydride MgTiVCrFe-H for hydrogen storage [75], high-entropy oxide TiZrHfNbTaO 11 for photocatalytic hydrogen production [76] and high-entropy oxynitride TiZrHfNbTaO 6 N 3 as a photocatalyst with large light absorbance [77]. 3…”