Electrochemically deposited Cu 2 O cubic particles on boron doped diamond substrate as efficient photocathode for solar hydrogen generation

At a Glance

Metadata	Details
Publication Date	2017-02-22
Journal	Applied Surface Science
Authors	Christos K. Mavrokefalos, Maksudul Hasan, James F. Rohan, Richard G. Compton, John S. Foord
Institutions	University College Cork, University of Oxford
Citations	40
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Efficiency BDD Photocathodes for Solar Hydrogen Generation

Reference Paper: Mavrokefalos et al., “Electrochemically deposited Cu₂O cubic particles on boron doped diamond substrate as efficient photocathode for solar hydrogen generation,” Applied Surface Science (2017).

Executive Summary

This research validates Boron-Doped Diamond (BDD) as a superior, stable substrate for high-performance photoelectrochemical (PEC) water splitting, directly aligning with 6CCVD’s core material offerings for energy applications.

High Performance Achieved: The NiO-Cu₂O/BDD photocathode demonstrated a maximum photoconversion efficiency of 0.28% and a peak photocurrent density of -0.42 mA/cm² at 0.0 V vs. RHE.
BDD as Enabling Substrate: The use of highly conductive BDD (doping >10²⁰ cm^-3) provides a wide potential window, resistance to fouling, and stable chemical termination, facilitating enhanced charge separation.
Synergistic Co-Catalysis: Decoration of the p-type Cu₂O semiconductor with NiO nanoparticles acts as an electron conduction mediator, significantly suppressing electron-hole recombination losses.
Stability and Retention: Optimized NiO loading (15 cycles) resulted in a stable electrode, retaining 70% of its initial photocurrent density over a 30-minute operational period.
High Carrier Density: The fabricated NiO-Cu₂O/BDD particles exhibited charge carrier densities on the order of 10²¹ cm^-3, an order of magnitude higher than typical Cu₂O films reported in literature.
Low-Cost Pathway: The methodology utilizes electrochemical deposition and dip coating, positioning BDD as a viable, low-cost catalyst support for scalable solar fuel production.

Technical Specifications

Parameter	Value	Unit	Context
BDD Doping Concentration	>10²⁰	cm^-3	High conductivity requirement for PEC.
BDD Wafer Dimensions	10 x 10 x 0.6	mm	Substrate size used for testing (1 cm² exposed area).
Maximum Photocurrent Density	-0.42	mA/cm²	Achieved by NiO(15)-Cu₂O/BDD at 0.0 V vs. RHE.
Photoconversion Efficiency (Max)	0.28	%	Achieved by NiO(6)-Cu₂O/BDD at -0.5 V vs. Pt.
Unmodified Efficiency (Baseline)	0.06	%	Cu₂O/BDD baseline efficiency.
Photocurrent Stability (Retention)	70	%	Current retained after 30 minutes (NiO(15)-Cu₂O/BDD).
Charge Carrier Density (N_A)	1.60 x 10²¹	cm^-3	Highest density achieved (NiO(15)-Cu₂O/BDD).
Cu₂O Band Gap	2.17	eV	Direct band gap of the p-type semiconductor.
NiO Nanoparticle Size	3 - 6	nm	Measured from high magnification TEM images.
Annealing Temperature	200	°C	Used for NiO coating precursor conversion.
Illumination Intensity	100	mW/cm²	1 sun AM 1.5 solar simulator intensity.
Electrolyte pH	6.5	N/A	Aqueous 0.1M Na₂SO₄ solution.

Key Methodologies

The fabrication of the high-efficiency photocathode involved a two-step process utilizing 6CCVD’s core material (BDD) as the foundation.

BDD Substrate Preparation:
- BDD solid wafers (10 x 10 x 0.6 mm) with high boron doping (>10²⁰ cm^-3) were used as the working electrode.
- A 1 cm² area was exposed to the electrolyte.
Cu₂O Electrodeposition (Galvanostatic):
- Cu₂O catalyst was deposited onto the BDD from a surfactant-free electrolyte (1.5M lactic acid, 1.9M NaOH, 0.2M CuSO₄·5H₂O).
- Deposition was performed galvanostatically at a current of -6.6 mA (vs. Ag/AgCl) for 60 seconds.
- SEM confirmed the resulting Cu₂O particles were cubic in shape.
NiO Nanoparticle Decoration (Dip Coating & Annealing):
- The Cu₂O/BDD electrode was modified using a dip coating method.
- Precursor solution: 0.5M nickel acetate in 0.5M ethanolamine and 2-methyloxyethanol.
- Dip coating speed: 0.35 cm/min.
- Intermediate drying: Pre-heated oven at 200 °C for 5 minutes between cycles.
- Optimization: The procedure was repeated up to 20 times; NiO(6) and NiO(15) coatings showed optimal PEC performance and stability, respectively.
- Final Annealing: 200 °C in air for 3 hours.
Photoelectrochemical Testing:
- Measurements conducted in a three-electrode cell (Pt counter, Ag/AgCl reference) in 0.1M Na₂SO₄ (pH 6.5).
- Illumination provided by a 100W Xenon lamp (AM 1.5 filter, 100 mW/cm²).
- Performance characterized by Linear Sweep Voltammetry (LSV) under chopped light (0.2 Hz) and Electrochemical Impedance Spectroscopy (EIS).

6CCVD Solutions & Capabilities

This research demonstrates the critical role of high-quality, highly conductive Boron-Doped Diamond (BDD) substrates in achieving state-of-the-art photoelectrochemical performance. 6CCVD is uniquely positioned to supply the foundational diamond material required to replicate and scale this technology.

Applicable Materials

To replicate the high-performance photocathode described, researchers require BDD substrates with exceptional conductivity and surface quality.

6CCVD Material Recommendation	Specification Match	Value Proposition
Heavy Boron-Doped PCD Wafers	Doping >10²⁰ cm^-3	Ensures the necessary high conductivity (metallic regime) required for efficient charge transfer and low resistance, matching the paper’s requirements.
PEC Grade SCD or PCD	Thickness 0.5 mm - 1.0 mm	We offer substrates up to 10mm thick, providing robust mechanical support for large-area PEC cells and ensuring thermal stability during subsequent high-temperature processing (e.g., annealing).
Polished BDD Substrates	Ra < 5 nm (PCD)	Highly polished surfaces minimize defects, providing a uniform foundation for subsequent electrochemical deposition of Cu₂O cubic particles, ensuring consistent catalyst morphology and performance across the wafer.

Customization Potential

The success of this research hinges on precise material dimensions and the ability to integrate external contacts. 6CCVD offers comprehensive customization services to optimize BDD for industrial PEC scale-up.

Large Area Scaling: While the paper used 1 cm² working area, 6CCVD can supply Polycrystalline Diamond (PCD) wafers up to 125 mm in diameter, enabling the transition from lab-scale testing to commercial-scale solar fuel reactors.
Custom Dimensions and Thickness: We provide BDD plates cut to exact specifications (e.g., 10 x 10 x 0.6 mm or larger custom shapes) and can control thickness from 0.1 µm up to 500 µm for active layers, or up to 10 mm for structural substrates.
Integrated Metalization: For robust electrical connection in PEC cells, 6CCVD offers in-house metalization services. We can deposit standard contact layers (e.g., Ti/Au, Pt, W) directly onto the BDD back surface, ensuring low-resistance ohmic contacts essential for device integration.

Engineering Support

The synergistic effect observed between the BDD substrate and the NiO-Cu₂O catalyst highlights the importance of material interface engineering.

Interface Optimization: 6CCVD’s in-house PhD team specializes in CVD diamond surface termination and doping control. We can assist researchers in optimizing BDD material selection (e.g., surface termination, doping profile) to maximize the electronic coupling and charge transfer rates for similar Solar Hydrogen Generation projects.
Global Supply Chain: We ensure reliable, global shipping (DDU default, DDP available) of high-purity MPCVD diamond materials, minimizing lead times for critical research timelines.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

DOI: https://doi.org/10.1016/j.apsusc.2017.02.148

References

2010 - Visible light response photocatalytic water splitting over CdS-pillared zirconium-titanium phosphate (ZTP) [Crossref]
2011 - Efficient hydrogen production by composite photocatalyst CdS-ZnS/Zirconium-titanium phosphate (ZTP) under visible light illumination [Crossref]
2012 - Facile synthesis of visible light responsive V2O5/N,S-TiO2 composite photocatalyst: enhanced hydrigen production and phenol degradation [Crossref]
2011 - Polarity-dependent photoelectrochemical activity in ZnO nanostructures for solar water splitting [Crossref]
2013 - A monolithic photovoltaic-photoelectrochemical device fro hydrogen production via water splitting [Crossref]
2010 - Solar water splitting cells [Crossref]
1999 - A realizable renewable energy future [Crossref]
2010 - Semiconductor-based photocatalytic hydrogen generation [Crossref]
2011 - Supported metal oxide nanosystems from hydrogen photogeneration: Quo vadis? [Crossref]