Dual Protection Layer Strategy to Increase Photoelectrode–Catalyst Interfacial Stability: A Case Study on Black Silicon Photoelectrodes

Abstract

sunlight is sufficient to supply the ≈18 TW of energy required to meet our current global energy needs [2] and sustain our soci ety's projected energy demands (≈80 TW to carry society through the end of this century). [1][2][3][4] This enormous potential within solar energy systems has aroused great interest in the scientific commu nity. Numerous strategies to harvest solar energy have been proposed and studied, such as photovoltaics, [5] water splitting, [6][7][8][9] and artificial photosynthesis of organic molecules. [10] Of particular interest to this group is photoelectrochemical (PEC) hydrogen production, by means of photo induced electrochemical conversion. PEC systems prove to be promising and prac tical due to hydrogen's abilities as a clean chemical fuel that can be stored, trans ferred, and redistributed to meet our ever increasing energy demands.A key component of PEC systems is the presence of an efficient photoabsorber able to instantly and effectively absorb and convert solar irradiation into electrical energy. Silicon (Si) has been widely inves tigated and employed in PEC systems due to its high abundance and low cost. [11,12] Its narrow bandgap of 1.12 eV suggests that Si is suitable to absorb a wide wave length range, making it advantageous in comparison with other semiconductor materials. Si's bandgap is slightly lower than overall water splitting energetics (1.23 eV), while its conduction Photoelectrode degradation under harsh solution conditions continues to be a major hurdle for long-term operation and large-scale implementation of solar fuel conversion. In this study, a dual-layer TiO 2 protection strategy is presented to improve the interfacial durability between nanoporous black silicon and photocatalysts. Nanoporous silicon photocathodes decorated with catalysts are passivated twice, providing an intermediate TiO 2 layer between the substrate and catalyst and an additional TiO 2 layer on top of the catalysts. Atomic layer deposition of TiO 2 ensures uniform coverage of both the nanoporous silicon substrate and the catalysts.After 24 h of electrolysis at pH = 0.3, unprotected photocathodes layered with platinum and molybdenum sulfide retain only 30% and 20% of their photocurrent, respectively. At the same pH, photocathodes layered with TiO 2 experience an increase in photocurrent retention: 85% for platinum-coated photocathodes and 91% for molybdenum sulfide-coated photocathodes. Under alkaline conditions, unprotected photocathodes experience a 95% loss in photocurrent within the first 4 h of electrolysis. In contrast, TiO 2 -protected photocathodes maintain 70% of their photocurrent during 12 h of electrolysis. This approach is quite general and may be employed as a protection strategy for a variety of photoabsorber-catalyst interfaces under both acidic and basic electrolyte conditions.

Recent Progress of Black Silicon: From Fabrications to Applications

“…However, the intrinsic surface morphology of black silicon hinders the hydrophilicity of photocatalytic films. In 2019, San Diego State University fabricated black silicon from metal-assisted etching silicon wafers [ 85 ]. The researchers sequentially deposited titanium dioxide films, platinum nanoparticles, and titanium dioxide films on the surface to achieve the protection of strong acids and strong bases.…”

“…Black silicon has excellent absorption and low reflectance in the NIR band. Since the late 1990s, when Eric Mazur, a professor at Harvard University, discovered black silicon by accident [ 9 ], researchers have been exploring its application to infrared photodetection [ 47 , 63 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 ] and ultrahigh sensitivity in the ultraviolet band and visible light range [ 90 , 91 , 92 ].…”

Semiconductor-based photocatalysts for photocatalytic and photoelectrochemical water splitting: will we stop with photocorrosion?

“…The prepared photoelectrodes with such a dual-TiO 2 -layer sandwich structure exhibited more excellent stability than a single (TiO 2 / Pt/bSi, Pt/TiO 2 /bSi) or non-protective layer (Pt/bSi). 90 Other photoelectrodes with a similar sandwich structure were also reported by the Chidsey group. 91 Furthermore, Gu and coworker designed a GaInP 2 photocathode with a graded catalytic-protective layer by annealing an amorphous-MoS x / TiO x -GaInP 2 stack at 450 C. 92 Annealing treatment resulted in a large degree of mutual penetration between MoS x , TiO 2 and GaInP 2 , while there was a relatively clear boundary between the components before annealing.…”

Structure‐Induced Stability in Sinuous Black Silicon for Enhanced Hydrogen Evolution Reaction Performance

“…Several studies have attempted to surpass this limit using dual‐layer schemes, including one focused on protecting the semiconductor–catalyst interface as well as the semiconductor itself. [ 22 ] In this study, a 20 nm‐layer of TiO 2 was deposited onto c‐bSi before depositing the catalyst. A second 2 nm‐TiO 2 layer was deposited atop the catalyst to protect the semiconductor–catalyst interface, resulting in stability for 110 h. While these results are promising, ALD is an expensive technique which has not been realized for large‐scale use, thus, there remains a need to stabilize the bSi surface without requiring an additional protective layer.…”