Improved solar hydrogen production by engineered doping of InGaN/GaN axial heterojunctions

Abstract

InGaN-based nanowires (NWs) have been investigated as efficient photoelectrochemical (PEC) water splitting devices. In this work, the InGaN/GaN NWs were grown by molecular beam epitaxy (MBE) having InGaN segments on top of GaN seeds. Three axial heterojunction structures were constructed with different doping types and levels, namely n-InGaN/n-GaN NWs, undoped (u)-InGaN/p-GaN NWs, and p-InGaN/p-GaN NWs. With the carrier concentrations estimated by Mott-Schottky measurements, a PC1D simulation further confirmed the band structures of the three heterojunctions. The u-InGaN/p-GaN and p-InGaN/p-GaN NWs exhibited optimized stability in pH 0 electrolytes for over 10 h with a photocurrent density of about -4.0 and -9.4 mA/cm 2 , respectively. However, the hydrogen and oxygen evolution rates of the Pt-treated u-InGaN/p-GaN NWs exhibited a less favorable stoichiometric ratio. On the other hand, the Pt-decorated p-InGaN/p-GaN NWs showed the best PEC performance, generating approximately 1000 µmol/cm 2 hydrogen and 550 µmol/cm 2 oxygen in 10 h. The band-engineered p-InGaN/p-GaN axial NWsheterojunction demonstrated a great potential for highly efficient and durable photocathodes.

Modulating Surface/Interface Structure of Emerging InGaN Nanowires for Efficient Photoelectrochemical Water Splitting

“…Afterwards, this group further constructed different axial heterostructures doped with Si and/or Mg including n‐InGaN/n‐GaN NWs, undoped (u)‐InGaN/p‐GaN NWs, and p‐InGaN/p‐GaN NWs. [ 110 ] The optimized band structure of the p‐InGaN/p‐GaN NWs elevates anodic HER. As shown in Figure a, photo‐extracted holes accumulated on n‐InGaN/n‐GaN NWs surface readily participate in cathodic OER.…”

“…d) LSV curves,and e) chronoamperometry measurements and f) hydrogen and oxygen evolution for the InGaN/GaN NWs photoelectrode (the photoanodes and photocathodes were tested in pH 7 and pH 0 electrolytes, respectively, under 6 suns AM 1.5 G illumination). Reproduced with permission [110]. Copyright 2019, The Optical Society.…”

Highly Efficient Photoelectrochemical Water Splitting Using GaN-Nanowire Photoanode with Tungsten Sulfides

“…According to the previous works, however, the current density of the photoanodes using metal oxides was measured to be less than 1 mA/cm 2 and therefore, needs to be improved. Recently, a III-nitride material system has been reported as a potential candidate for PEC-WS which has the merit of possessing a tunable band gap that spans nearly the entire solar spectrum, and good corrosion resistance in aqueous solution. − Among them, a GaN nanowire (NW) has been suggested as an effective medium to improve PEC-WS performance due to its large surface-to-volume ratio, strong separation of photogenerated carriers, and enhanced optical absorption coefficient. − Most importantly, the conduction-band minimum (CBM) and the valence-band maximum (VBM) of GaN NWs can straddle the water redox potentials, facilitating a highly stable and efficient PEC-WS . However, III-nitride NWs have pronounced surface states, thereby providing surface Fermi-level pinning to the carriers, which leads to Shockley-Read-Hall nonradiative recombination and indirect recombination related to the radial Stark effect. , To improve the efficiency of PEC-WS, noble metals such as Pt and Au were used to reduce the effect of surface states of the GaN NWs.…”

Drastic improvement in photoelectrochemical water splitting performance over prolonged reaction time using new carrier-guiding semiconductor nanostructures

“…[1][2][3] Because hydrogen is generated directly at the photocathode (PC) in the PEC-WS cell, the materials used to fabricate the PC have been actively researched in an attempt to maximize the PEC-WS efficiency. 4,5 Previous representative results on PCs fabricated with various materials and structures are summarized in Table 1, [6][7][8][9][10][11][12][13][14][15][16][17][18] where the current density, applied-bias photon-to-current efficiency (ABPE), and the amount of hydrogen gas generated from the PC for the PEC-WS are less than 25 mA cm À2 , 5%, and 1.5 mmol, respectively. 10,13 Moreover, previous studies found that the performance of the PCs signicantly degraded with respect to the reaction time.…”

“…Considering the previous representative results listed in Table 1, the current density of the InGaN/GaN-CSNW PC fabricated in the present work is much higher than those of the PCs in previous studies, irrespective of their material composition and structure. [6][7][8][9][10][11][12][13][14][15][16][17][18] Fig. 2d shows the ABPE derived from the J-V characteristic curves of the InGaN/GaN-CSNW PC.…”