Electrochemical Looping Green Hydrogen Production by Using Water Electrochemically Treated as a Raw Material for the Electrolyzer

At a Glance

Metadata	Details
Publication Date	2025-05-02
Journal	Catalysts
Authors	Mayra Kerolly Sales Monteiro, Jussara Câmara Cardozo, Aruzza Mabel de Morais Araújo, Amanda Duarte Gondim, Tabata Natasha Feijoó Zambrano
Institutions	National Agency of Petroleum, Natural Gas and Biofuels, Universidade Federal do Rio Grande do Norte
Citations	1
Analysis	Full AI Review Included

Technical Documentation & Analysis: Electrochemical Looping Green Hydrogen Production

Executive Summary

This document analyzes the application of Boron-Doped Diamond (BDD) electrodes in an integrated-hybrid electrochemical system designed for simultaneous wastewater treatment and green hydrogen (H₂) production. The core findings validate a sustainable “win-win” strategy, directly aligning with 6CCVD’s advanced MPCVD diamond capabilities.

Dual Sustainability Goal Achieved: The system successfully demonstrated high-efficiency removal of organic pollutants from raw municipal effluent while simultaneously generating green H₂.
High Mineralization Efficiency: Using a BDD/Nb anode at 90 mA cm^-2, the system achieved 99% Chemical Oxygen Demand (COD) removal and reduced Total Organic Carbon (TOC) from 638 mg L^-1 to 8.3 mg L^-1 within 180 minutes.
BDD Performance Validation: The BDD electrode proved superior due to its high oxygen evolution potential (~+2.25 V), promoting the formation of highly oxidizing hydroxyl radicals (•OH) necessary for rapid organic matter degradation.
Green H₂ Production & Reuse: Over 1.3 L of H₂ gas was produced in 180 minutes at 90 mA cm^-2, achieving 100% Faradaic efficiency in the initial step. Crucially, the electrochemically treated water was successfully reused in the cathodic compartment, demonstrating that clean water is not required for sustainable H₂ generation.
Energy and Cost Optimization: The hybrid process, driven by a photovoltaic (PV) system, showed lower energy consumption when reusing treated water compared to using standard electrolyte solutions, minimizing operating costs and fulfilling SDG 7 (Affordable and Clean Energy).
Material Durability: The use of BDD supported on Niobium (Nb) was highlighted as a stable material suitable for long-term, large-scale applications, demonstrating lifespans exceeding 850 hours under harsh conditions.

Technical Specifications

Parameter	Value	Unit	Context
Anode Material	Boron-Doped Diamond (BDD)	N/A	Supported on Niobium (Nb)
Cathode Material	Ni-Fe-based SS Mesh	N/A	Noble-metal free, low cost
Current Densities ($j$) Applied	30, 60, 90	mA cm^-2	Galvanostatic control
Electrolysis Time	180	min	Total treatment time
Operating Temperature	25	°C	Ambient conditions
Initial Raw TOC	638	mg L^-1	Municipal effluent
Final Treated TOC (90 mA cm^-2)	8.3	mg L^-1	After 180 min EO treatment
COD Removal Efficiency	99	%	Achieved at 90 mA cm^-2
H₂ Volume Produced (90 mA cm^-2)	>1.3	L	After 180 min electrolysis
Faradaic Efficiency (Initial Step)	100	%	H₂ production compared to theoretical
H₂ Energy Efficiency (H₂EE)	37 - 44	%	Range across 90 mA cm^-2 to 30 mA cm^-2
BDD Oxygen Evolution Potential	~+2.25	V	Voltammetric profile in 0.1 mol L^-1 Na₂SO₄
BDD Substrate Lifespan (Nb)	>850	h	Under acidic conditions (0.5 M H₂SO₄)

Key Methodologies

The integrated-hybrid electrochemical looping process was conducted in a divided-membrane cell (Nafion type-350 separator) using a PV energy source under galvanostatic control.

Electrode Configuration: A BDD film supported on Nb served as the anode for Electrochemical Oxidation (EO), and a Ni-Fe-based Stainless Steel (SS) mesh served as the cathode for H₂ production.
Electrolyte Preparation: Raw municipal wastewater was used in the anodic compartment, supplemented with 0.1 mol L^-1 Na₂SO₄ supporting electrolyte.
Stage 1 (Treatment & Production): The effluent was recirculated through the anodic compartment (350 mL volume) at a constant rate (125 mL min^-1) while H₂ was simultaneously produced in the cathodic compartment (40 mL volume of supporting electrolyte). Current densities of 30, 60, and 90 mA cm^-2 were applied for 180 minutes.
Water Quality Assessment: Water quality parameters (COD, TOC, pH, conductivity, organic acids) were analyzed after the anodic treatment to confirm high-quality water parameters were reached.
Stage 2 (Looping & Reuse): The electrochemically treated water (from Stage 1) was then reused in the cathodic compartment (without additional electrolyte) for a new H₂ production run under the same current densities, validating the looping strategy.
Gas Analysis: Differential Electrochemical Mass Spectroscopy (DEMS) was used to monitor the composition and purity of the H₂ gas produced at the cathode.

6CCVD Solutions & Capabilities

The research successfully demonstrates the critical role of high-performance BDD electrodes in sustainable water-to-energy conversion. 6CCVD is uniquely positioned to supply and scale the required diamond materials for replicating and advancing this technology.

Applicable Materials

To replicate the high efficiency and durability demonstrated in this study, researchers require Boron-Doped Diamond (BDD) electrodes with specific characteristics:

Research Requirement	6CCVD Material Solution	Technical Advantage
High Performance Anode	Heavy Boron-Doped PCD (Polycrystalline Diamond)	High doping concentration ensures low resistivity and the necessary high overpotential (~+2.25 V) for efficient hydroxyl radical generation (EO).
Substrate Durability	Custom Substrate BDD (Nb, Ti, W)	While the paper used Nb, 6CCVD offers BDD films deposited on various conductive substrates (Nb, Ti, W) suitable for harsh, acidic electrochemical environments, ensuring long operational lifespans (>850 h).
Cathode Material	Standard PCD or SCD Substrates	While the paper used Ni-Fe mesh, 6CCVD can provide high-purity diamond substrates (SCD or PCD) for researchers investigating novel H₂ evolution catalysts (e.g., deposited Pt or Ni alloys) on diamond supports.

Customization Potential for Scale-Up

The successful implementation of this hybrid process relies on scaling up the BDD electrode area to handle larger effluent volumes and higher current loads.

Large-Area BDD Plates: 6CCVD specializes in MPCVD diamond plates and wafers up to 125mm (PCD). This capability directly supports the transition from laboratory-scale cells (as used in the paper) to industrial reactors required for high-volume wastewater treatment and H₂ generation.
Custom Thickness Control: We offer precise control over BDD film thickness, ranging from 0.1µm to 500µm. This allows engineers to optimize the balance between cost, conductivity, and mechanical stability for specific reactor designs.
Advanced Metalization Services: For robust electrical connections and integration into flow cells, 6CCVD provides in-house custom metalization using materials such as Ti, Pt, Au, and W. This ensures reliable contact layers essential for high current density operation (up to 90 mA cm^-2 and beyond).
Precision Fabrication: 6CCVD offers precision laser cutting and shaping services to produce custom electrode geometries required for divided-membrane cells or specialized flow reactors.

Engineering Support

The paper highlights that BDD/Nb electrodes maintain stability for over 850 hours under severe conditions. 6CCVD’s in-house PhD team possesses deep expertise in diamond electrochemistry and can assist clients in:

Material Selection: Guiding the choice between PCD and SCD, and selecting the optimal substrate (Nb, Ti, Si) and doping level to maximize the lifespan and efficiency of BDD anodes for similar wastewater treatment and green H₂ production projects.
Performance Optimization: Consulting on surface preparation (polishing Ra < 5nm for PCD) and metal contact design to minimize ohmic losses and maximize H₂EE (Energy Efficiency).
Global Supply Chain: Ensuring reliable, DDU (Delivered Duty Unpaid) default, or DDP (Delivered Duty Paid) global shipping for time-sensitive research and development projects.

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

View Original Abstract

In this study, the applicability of an integrated-hybrid process was performed in a divided electrochemical cell for removing organic matter from a polluted effluent with simultaneous production of green H2. After that, the depolluted water was reused, for the first time, in the cathodic compartment once again, in the same cell to be a viable environmental alternative for converting water into energy (green H2) with higher efficiency and reasonable cost requirements. The production of green H2 in the cathodic compartment (Ni-Fe-based steel stainless (SS) mesh as cathode), in concomitance with the electrochemical oxidation (EO) of wastewater in the anodic compartment (boron-doped diamond (BDD) supported in Nb as anode), was studied (by applying different current densities (j = 30, 60 and 90 mA cm−2) at 25 °C) in a divided-membrane type electrochemical cell driven by a photovoltaic (PV) energy source. The results clearly showed that, in the first step, the water anodically treated by applying 90 mA cm−2 for 180 min reached high-quality water parameters. Meanwhile, green H2 production was greater than 1.3 L, with a Faradaic efficiency of 100%. Then, in a second step, the water anodically treated was reused in the cathodic compartment again for a new integrated-hybrid process with the same electrodes under the same experimental conditions. The results showed that the reuse of water in the cathodic compartment is a sustainable strategy to produce green H2 when compared to the electrolysis using clean water. Finally, two implied benefits of the proposed process are the production of green H2 and wastewater cleanup, both of which are equally significant and sustainable. The possible use of H2 as an energetic carrier in developing nations is a final point about sustainability improvements. This is a win-win solution.

Tech Support

Original Source

DOI: https://doi.org/10.3390/catal15050447

References

2022 - An Overview of Water Electrolysis Technologies for Green Hydrogen Production [Crossref]
2021 - Recent Development in Electrocatalysts for Hydrogen Production through Water Electrolysis [Crossref]
2020 - Cathodic Hydrogen Production by Simultaneous Oxidation of Methyl Red and 2,4-Dichlorophenoxyacetate Aqueous Solutions Using Pb/PbO2, Ti/Sb-Doped SnO2 and Si/BDD Anodes. Part 1: Electrochemical Oxidation [Crossref]
2020 - Cathodic Hydrogen Production by Simultaneous Oxidation of Methyl Red and 2,4-Dichlorophenoxyacetate in Aqueous Solutions Using PbO2, Sb-Doped SnO2 and Si/BDD Anodes. Part 2: Hydrogen Production [Crossref]
2024 - Energy-Saving Electrochemical Green Hydrogen Production Coupled with Persulfate or Hydrogen Peroxide Valorization at Boron-Doped Diamond Electrodes [Crossref]
2023 - A Sustainable Solar-Driven Electrochemical Process for Reforming Lignocellulosic Biomass Effluent into High Value-Added Products: Green Hydrogen, Carboxylic and Vanillic Acids [Crossref]
2023 - Electrochemical Oxidation of a Real Effluent Using Selective Cathodic and Anodic Strategies to Simultaneously Produce High Value-Added Compounds: Green Hydrogen and Carboxylic Acids [Crossref]
2024 - Replacing Oxygen Evolution Reaction in Water Splitting Process by Electrochemical Energy-Efficient Production of High-Added Value Chemicals with Co-Generation of Green Hydrogen [Crossref]