Water Interaction with Sputter-Deposited Nickel Oxide on n-Si Photoanode: Cryo Photoelectron Spectroscopy on Adsorbed Water in the Frozen Electrolyte Approach

Abstract

The interaction of water with a magnetron-sputtered nickel oxide thin film on an n-type silicon photoanode is investigated in perspective to oxygen evolution. The substrate was exposed in-situ stepwise to gas phase water up to 10 L at liquid N 2 temperature and analyzed via X-ray and UV photoelectron spectroscopy in the so called frozen electrolyte approach. Photoemission of the pristine NiO x layer shows the presence of stoichiometric NiO and Ni 2 O 3 as well as of non-stoichiometric phases. In the monolayer range, molecular and dissociative adsorption is detected assigned to the NiO respective Ni 2 O 3 phase. Initially, the emission of the molecular adsorbed water species interacting with NiO is found at 0.8 eV lower binding energies as compared to water related emission for higher coverages with binding energies commonly assigned to H 2 O-H 2 O interaction. In addition to the chemical analysis, the electronic structure of the n-Si/SiO Most semiconducting materials, especially silicon, are unstable and degrade or passivate rapidly under photoanodic conditions in aqueous electrolytes.1 Nickel oxide thin films are promising catalysts for the hydrogen and the oxygen evolution reaction (OER) 2 and provide chemically stable coatings for silicon, while being transparent, antireflective and electronically conductive in addition.3-5 Elementary charge transfer processes located at a solid/liquid interface, are still scarcely approached by scientific studies on an atomistic scale.6 Especially the energetics of the photocatalytic dissociation of water on semiconducting materials is still unclear. In general, the determination of the chemical and electronic interaction at the interface between metal oxides and liquid electrolytes on an atomistic scale via surface science methods suffers from the so-called pressure gap. 7,8 One way to bridge the gap, model experiments at low temperatures can be utilized to monitor the surface chemistry by means of photoelectron spectroscopy under ultra-high vacuum. Regarding double layer formation, the frozen-electrolyte approach has already shown its potential in the past. 9 The principle mechanism of the oxygen evolution (OER) at nickel hydroxide based electrodes was investigated early on a more chemical basis 10 with various phase transitions involved. 11 It has been found that Ni(OH) 2 and NiOOH species at the surface are a prerequisite for any photocatalytic activity. However, the exact mechanism is still under debate 12 with the role of nickel oxide only little discussed. A first step for a better understanding is to study the reactivity of a pristine nickel oxide surface upon water adsorption. For NiO(100) it has been demonstrated that a perfect surface exhibits no reactive interaction with H 2 O unless oxygen vacancies induce the dissociation of water 13 or adsorbed O 2− ions at defect sites on a pre-oxidized surface enhance the reactivity. In contrast to NiO(100), theoretical studies predict dissociative water adsorption for NiO(111).14 Further to oxygen vacancies sub-coordinated ...

Mesoporous Ternary Nitrides of Earth-Abundant Metals as Oxygen Evolution Electrocatalyst

“…This behavior is also supported by the O 1s high-resolution scans (Fig. 3d), where the O 1s of Ni 3 FeO x has a strong feature at 529.6 eV ascribed to NiO [39], which greatly diminished with nitridation. For the mixed metal nitride, there is also evidence of an iron hydroxide phase, at 532.2 eV [40,41].…”

Rational Design and Construction of Cocatalysts for Semiconductor‐Based Photo‐Electrochemical Oxygen Evolution: A Comprehensive Review

“…This core/ shell hybrid broke the efficiency limit of pristine ZnO and achieved a remarkable 260 mV negative shift of onset potential for photo-oxidation of water. [147] In addition, Fingerle et al [148] took a magnetron-sputtering method to deposit nickel oxide on the n-Si/SiO x photoanode and described the interaction of NiO x layer and H 2 O at the electrode/electrolyte interface, which was beneficial for the hole transport. The band alignment between them offered efficient carrier separation and fast hole transport, making its PEC performance significantly outperform that of pure GaN.…”

“…Besides, an n‐silicon photoanode coated by a NiO x layer was successfully synthesized via a pulsed laser deposition method for efficient PEC oxygen evolution . In addition, Fingerle et al took a magnetron‐sputtering method to deposit nickel oxide on the n‐Si/SiO x photoanode and described the interaction of NiO x layer and H 2 O at the electrode/electrolyte interface, which was beneficial for the hole transport. All these investigations confirm that nickel oxides can be deposited onto the surface of photoanodes with different methods in order to satisfy various requirements and then gain a better performance.…”

Metal Chalcogenides on Silicon Photocathodes for Efficient Water Splitting: A Mini Overview

“…They confirmed the stepwise energy level of the electrode and the conduction band minimum (CBM) position shift of the materials. Fingerle et al made a schematic model interface model of nickel oxide/water to investigate the role of nickel oxide as an OER catalyst and water adsorption surface chemistry from the results of XPS core level and UPS valence band analysis [119] Wan et al analyzed the Fermi level of SrNbO 3 with a 1 wt % of platinum powder co-catalyst with UPS analysis [120]. Liu et al used He I source (21.22 eV) UPS to determine the ionization potential (equivalent to the valence band energy) of C 3 N 4 [121].…”