Interstitial M<sup>+</sup> (M<sup>+</sup> = Li<sup>+</sup> or Sn<sup>4+</sup>) Doping at Interfacial BiVO<sub>4</sub>/WO<sub>3</sub> to Promote Photoelectrochemical Hydrogen Production
Santosh S. Patil, Jaewon Lee, Eunoak Park, N. Lakshmana Reddy, Kiyoung Lee
Abstract
Doping metals together with heterostructure assemblages is critical to address the challenges encountered while using bismuth vanadate (BVO) to yield improved light-harvesting, charge transfer, and solar-to-hydrogen conversion efficiency. To date, most approaches have focused on substitutional doping using hexavalent metal ions (Mo6+ and W6+) at vanadium or bismuth sites to improve the photoelectrochemical (PEC) performance. Unlike conventional substitution, which produces V-substituted sites that function as hole traps and reduce the activity, herein, we used a simple hydrothermal and metal–organic decomposition approach to introduce interstitial [Li+ or Sn4+]n-doping in BVO (n = 0.25, 0.5, 1.0, 1.5, and 2.0 mM) interfaced with tungsten oxide (WO). The resulting Sn-doped BVO/WO (0.5 mM) shows a reproducible photocurrent density of 1.65 ± 0.07 mA cm–2 and 4.28 ± 0.15 mA cm–2 at 1.23 VRHE for water oxidation and sulfite oxidation, respectively, with a superior quantum efficiency (60% at 470 nm) and long-term durability (>10000 s) under standard AM 1.5 G light irradiation (1 sun). The results show that the Sn-doped BVO/WO exhibited an enhanced PEC performance approximately three times better than that of pristine BVO/WO, thus enabling continuous H2 production (∼800 μmol·cm–2) and highlighting the beneficial role of strategically controlled interstitial dopant concentration. Mott–Schottky analysis revealed an increase in the donor concentration for Li–BVO/WO (∼2.3-fold) and Sn–BVO/WO (3.5-fold), related to the reference BVO/WO photoelectrode. This work highlights the use of low-cost dopants and heterojunction photocatalysts to carry out hydrogen evolution reactions at a significantly improved rate.