High‐Performance and Stable Silicon Photoanode Modified by Crystalline Ni@ Amorphous Co Core‐Shell Nanoparticles

Abstract

Improving the charge separation and transport efficiency at semiconductor-electrolyte interface is critical for high-performance photoelectrochemical (PEC) water-splitting devices. Here, the core-shell-structured Ni@Co nanoislands were electrodeposited onto the surface of n-type Si photoanode to construct a metal-insulator-semiconductor (MIS) structure. We discover that the high-quality interface in Si/SiO x /Ni MIS structure is more efficient for charge extraction and transfer than Si/SiO x /Co. Owing to a slightly higher work function for Co (5.0 eV) than Ni (4.6 eV), the Si/SiO x /Ni@Co exhibits the larger band bending to enhance the charge separation efficiency, while the in-situ formed CoOOH significantly increases the charge injection efficiency due to the decreased oxygen-evolution overpotentials. As a result, the Ni@Co core-shell nanoparticles coupling with n-Si photoanode can afford the PEC performance with an onset potential of 1.02 V versus reversible hydrogen electrode (RHE), saturated current density of 36.7 mA cm À2 , and retain good stability in K-borate buffer solution. This core-shell structure strategy is efficient and easy to achieve the separation of photogenerated carriers and improve the charge injection efficiency to nearly 100 %[a] J.

Dissociating Water at n‐Si Photoanodes Partially Covered with Fe Catalysts

“…Recent reports by our group, and others, have demonstrated that aqueous electrodeposition of transition metals nanoparticles (NPs) on n‐Si is effective to prepare inhomogeneous Si/metal Schottky junctions that can be further employed as stable Si‐based photoanodes without protection layer. This type of photoanode has been reported, so far, for n‐Si/Ni and n‐Si/Co junctions and it has been recently shown that the performance of these systems can be enhanced by using an additional catalytic shell, typically a hydroxide, or a metallic coating, over the NPs. To the best of our knowledge, this phenomenon has never been applied to n‐Si/Fe junctions so far, which we present for the first time in this article.…”

Water oxidation with inhomogeneous metal-silicon interfaces

“…Electrodeposition conveniently allows triggering layer by layer modifications at the cocat level (allowing the generation of core-shell structures) and thus, is expected to quickly lead to progress in the optimization the catalytic aspect of these photoanodes. [77,79,84] In addition, progress will probably arise from studying other important considerations such as cocat geometry, adhesion, and surface distribution. Attention should also be paid to a crucial but often neglected aspect that is the photoanode stability when unbiased.…”

Quantifying Losses and Assessing the Photovoltage Limits in Metal–Insulator–Semiconductor Water Splitting Systems

“…Many insulators have been utilized in silicon‐based MIS photocatalyst systems. These include SiO 2 ,28–41 TiO 2 ,42–47 HfO 2 ,48,49 Al 2 O 3 ,42,50–53 SrTiO 3 ,54 and ZrO 2. 55 Initially, MIS systems were motivated by their ability to improve the chemical stability of semiconductors, but recently many design strategies have been identified to improve the efficiency of these systems.…”