Characterizing the Geometry and Quantifying the Impact of Nanoscopic Electrocatalyst/Semiconductor Interfaces under Solar Water Splitting Conditions

Abstract

The materials that are receiving the most attention in photoelectrochemical water splitting are metallic nanoparticle electrocatalysts (np‐EC) attached to the surface of a semiconductor (SC) light absorber. In these multicomponent systems, the interface between the semiconductor and electrocatalysts critically affects performance. However, the np‐EC/SC interface remains poorly understood as it is complex on atomic scales, dynamic under reaction conditions, and inaccessible to direct experimental probes. This contribution sheds light on how the electrocatalyst/semiconductor interface evolves under reaction conditions by investigating the behavior of nickel electrocatalysts (as nanoparticles and films) deposited on silicon semiconductors. Rigorous electrochemical experiments, interfacial atomistic characterization, and computational modeling are combined to demonstrate critical links between the atomistic features of the interface and the overall performance. It is shown that electrolyte‐induced atomistic changes to the interface lead to (1) modulation of the charge carrier fluxes and a dramatic decrease in the electron/hole recombination rates and (2) a change in the barrier height of the interface. Furthermore, the critical roles of nonidealities and electrocatalyst coverage due to interfacial geometry are explored. Each of these factors must be considered to optimize the design of metal/semiconductor interfaces which are broadly applicable to photoelectrocatalysis and photovoltaic research.

Silicon Photoelectrodes Prepared by Low-Cost Wet Methods for Solar Photoelectrocatalysis

“…Specifically, in the case of Ni-coated photoanodes, n-Si/SiO x , as well as its interface with the electrolyte, Ni, Ni(OH) 2 , NiO x , and NiOOH phase junctions could play an important role in the overall response of the electrode. These photoanodes also show unusual properties, the first one being their photovoltage that can exceed 0.4 V, 39,55 which is much higher than what is expected for their conformal n-Si/Ni counterparts. Indeed, because of Fermi level pinning, which typically occurs at semiconductor/metal junctions, the typical Schottky barrier for n-Si/Ni conformal junctions is rather small.…”

“…According to recent works, this phenomenon is caused by the formation of a silicide layer 56 or the suppression of electron current caused by the SiO x interlayer. 55 Besides, the socalled "pinch-off effect", i.e., the screening of low barrier regions occurring under a critical size regime, 54,57,58 has also been used by several groups to explain these surprisingly high photovoltages. In these models, the low barrier region is n-Si/Ni, 45 and the high barrier region is n-Si/SiO x , 53 n-Si/NiOOH, 45 or n-Si/NiO x , 42 depending on the reference.…”

Construction of MnxCoyO4/Ti electrocatalysts for efficient bifunctional water splitting

“…The spectral analysis of O 1s showed that the hydroxyl group and water existed on the surface of the material, which enhanced the hydrophilicity of the material, which was favorable for the electrocatalytic reaction. 50,51 The peak at 533.2 eV is due to the adsorption of the hydroxyl group and water on the surface of the material. 52,53 In summary, XPS detection results further indicate the presence of MnCo 2 O 4 nanoparticles in the samples.…”

Studies on Electron Escape Condition in Semiconductor Nanomaterials via Photodeposition Reaction

“…It is practical to improve the properties, as well as application performance of semiconductor nanomaterials, via surface modification and functionalization. Surface engineering of semiconductor materials includes the studies on geometry effects, surface defects, capping ligands, decomposition of nanoparticles or the nanoshell, and so on [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. During the last decades, studies on geometry effects on nanocrystal materials have attracted strong interest as a result of the possibility to tailor the materials.…”

“…Studies on geometry effects of nanomaterials revealed the effects of size, morphology, and surface structure for nanoparticles. Surface geometry effects directly affect the surface properties, including work function and surface energy, which will further affect the particle properties and surface functionalization [ 13 , 14 , 15 , 16 ]. Meanwhile, surface defect engineering has also been considered as a useful approach for the modification of electronic and chemical properties of semiconductor nanomaterials, which enhances their activity photocatalysts [ 17 , 18 , 19 , 20 ].…”