Investigation of diamond electrodes for photo‐electrochemistry

Abstract

Boron doped diamond (BDD) shows high chemical stability in contact with a liquid phase even under extreme pH conditions, high electrochemical activity, and allows very stable covalent functionalization on O-or N-terminated surfaces. It is therefore an excellent electrode material for many applications such as analytics, biosensors, and purification. Furthermore, the electrodes can be covalently functionalized with photosensitive dyes to generate photo currents. However, the energetic conditions and charge transfer mechanisms are not fully known and therefore have been investigated in this work. The focus was set on the energy band diagrams of nanocrystalline diamond (NCD) layers, especially on the flat-band potential V F and the band-bending w B in the space charge layer, for both O-and N-terminated surfaces, and the charge transfer mechanisms at the semiconductor/electrolyte phase-boundary, with or without electro-active organic dyes, such as manganese phthalocyanine. For this study NCD samples were grown by hot filament chemical vapor deposition (HFCVD) with a boron doping density N A ranging between 5.8 and 9.6 Â 10 20 cm À3 .The pristine surface was then processed by oxygen or ammonia plasma to modify the termination to O and NH 2 , respectively. After that a series of Mott-Schottky plots was measured for both terminations at several frequencies spanning from 3 Hz to 10 kHz and in two different electrolytes, namely 0.1 M H 2 SO 4 and 0.1 M KCl. The results showed nearly the same flat-band potential for both surface terminations, but a remarkable difference in the band-bending. The latter is most probably responsible for the better photoelectrical conversion observed in N-terminated NCD samples. The open-circuit potential (OCP) and chronoamperometric measurements performed after covalent functionalization of the samples with the color dyes revealed that only the N-terminated material delivered a measurable photocurrent. Although the global efficiency of the photoelectric conversion was low, these initial results show that by optimized selection of materials and modification technologies providing a proper match of the energy levels at all charge transfer steps, a higher energy output could be achieved.

Visible-light sensitization of boron-doped nanocrystalline diamond through non-covalent surface modification

“…13 Petkov et al 16 grafted manganese phthalocyanine on nanocrystalline BDD and obtained photocurrents of several tens of nA cm À2 upon monochromatic illumination with 770 nm light, but the currents were anodic (h + were assumed to be transferred to the LUMO of the excited dye). For the same system, Bechter et al 17 observed cathodic photocurrent, as expected for the p-type BDD.…”

“…39,40 This dispersion was often reported on various diamond electrodes, 36,38,41,42 including the diamond electrodes which were modified by light-harvesting dyes. 17 For the equivalent circuit shown in Fig. 3 (inset), the capacitance C is equal to the capacitance of the space-charge layer in the diamond electrode, that is C = C sc .…”

“…An obvious advantage of this synthetic strategy is that it avoids the complicated multi-step surface chemistry, as well as the often observed poor yield of direct covalent anchoring of dyes. [15][16][17][18]20 Experimental section Preparation and characterization of BDD layers Deposition of 0.5 mm thick BDD films was carried out in an ASTeX 5010 (Seki Technotron, Japan) Microwave Plasma Enhanced Chemical Vapor Deposition (MW PECVD) reactor. Fused silica substrates were nucleated with a colloidal suspension of a NanoAmando (NanoCarbon Research Institute Co., Japan) detonation diamond.…”

Photocatalytic reduction of nitrogen to ammonia on diamond thin films grown on metallic substrates

“…We used an inelastic mean free path of 1.8 nm based on experimental measurements in nanocrystalline diamond [16]. This frequency is commonly used for the characterization of diamond surfaces in aqueous solutions [17].…”

Electrochemical Determination of Sulphur‐containing Pharmaceuticals Using Boron‐doped Diamond Electrodes

“…The surface termination has a strong influence on the electroanalytical performance of BDD. For example, nanocrystalline NH 2 ‐terminated BDD exhibits an improved sensitivity in comparison to oxygen‐terminated BDD . For amino‐terminated BDD, sufficient stability of the termination and an enhanced electron transfer rate in comparison to oxygen‐terminated BDD has been reported .…”