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6CCVD Research

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

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2025-05-02
JournalCatalysts
AuthorsMayra Kerolly Sales Monteiro, Jussara Câmara Cardozo, Aruzza Mabel de Morais Araújo, Amanda Duarte Gondim, Tabata Natasha Feijoó Zambrano
InstitutionsUniversidade Federal do Rio Grande do Norte, National Agency of Petroleum, Natural Gas and Biofuels
Citations1
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research details an integrated electrochemical looping process designed for simultaneous wastewater cleanup and sustainable green hydrogen (H2) production, driven by photovoltaic (PV) energy.

  • Core Value Proposition: Achieves a “win-win” solution by coupling the electrochemical oxidation (EO) of real effluent with H2 generation, followed by the reuse of the treated water in the cathodic compartment for continued H2 production.
  • Performance Metrics: The system achieved up to 99% Chemical Oxygen Demand (COD) removal and reduced Total Organic Carbon (TOC) from 638 mg L-1 to 8.3 mg L-1 at the highest current density (90 mA cm-2).
  • H2 Production Efficiency: Produced >1.3 L of green H2 in 180 minutes (at 90 mA cm-2) with a Faradaic efficiency of 100% in the initial step.
  • Electrode Materials: Utilizes a highly stable Boron-Doped Diamond (BDD) supported on Niobium (Nb) as the anode and a low-cost, noble-metal-free Ni-Fe-based Stainless Steel (SS) mesh as the cathode.
  • Sustainability Improvement: Reusing the anodically treated water proved to be a viable and sustainable strategy for H2 production, minimizing reliance on clean water and reducing overall energy consumption compared to traditional clean water electrolysis.
  • Energy Cost: The process is highly cost-effective, with energy costs for the EO/H2 process ranging from 0.000034 to 0.00015 US$ (based on IRENA PV costs) depending on the applied current density.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Anode MaterialBDD on Nb-High electrocatalytic stability.
Cathode MaterialNi-Fe-based SS mesh-Low-cost, efficient H2 evolution catalyst.
Electrolysis Time180minStandard duration for treatment/production.
Max Current Density (j)90mA cm-2Condition yielding highest removal/production rates.
Initial COD (Raw Water)119mg L-1Real municipal effluent.
Max COD Removal99%Achieved at 90 mA cm-2.
Initial TOC (Raw Water)638mg L-1-
Final TOC (Treated Water)8.3mg L-1After 180 min at 90 mA cm-2.
Max H2 Volume Produced>1.3LAfter 180 min at 90 mA cm-2 (Step 1).
Faradaic Efficiency (H2)100%Measured during Step 1 (wastewater anolyte).
Max H2 Energy Efficiency (H2EE)44%Achieved at 30 mA cm-2.
H2EE at Max j37%Achieved at 90 mA cm-2.
Anode Recirculation Rate125mL min-1Flow rate maintained by peristaltic pump.
Supporting Electrolyte0.1mol L-1 Na2SO4Used in both compartments (Step 1).
Anode Compartment Volume350mL-
Cathode Compartment Volume40mL-
BDD Oxygen Evolution Potential+2.25VMeasured in 0.1 mol L-1 Na2SO4.

Key Methodologies

Section titled “Key Methodologies”

The integrated-hybrid process utilized a divided electrochemical cell (wastewater || H2 cell) separated by a Nafion type-350 cation exchange membrane.

  1. Electrochemical Setup: Experiments were performed under galvanostatic conditions (30, 60, and 90 mA cm-2) using a power supply connected to a solar photovoltaic (PV)-battery system.
  2. Anodic Treatment (Step 1): 350 mL of raw municipal effluent (spiked with 0.1 mol L-1 Na2SO4) was recirculated through the BDD/Nb anode compartment at 125 mL min-1 for 180 minutes. Organic matter was oxidized primarily by electrochemically generated hydroxyl radicals (•OH) and sulfate-based mediators.
  3. Cathodic Production (Step 1): Simultaneously, green H2 was produced at the Ni-Fe-based SS mesh cathode using 40 mL of 0.1 mol L-1 Na2SO4 solution (no flow).
  4. Electrochemical Looping (Step 2): The water treated in the anodic compartment (now depolluted) was collected, analyzed, and then reused as the electrolyte in the cathodic compartment for a new H2 production run under the same current densities.
  5. Gas Analysis: Differential Electrochemical Mass Spectroscopy (DEMS) was used to monitor the composition of the gas phase (H2, N2) produced at the cathode, confirming high H2 purity when reusing the treated water.
  6. Water Quality Analysis: COD was monitored using a cost-effective smartphone-based protocol. TOC, conductivity, pH, and organic acid intermediates (HPLC) were also measured to assess treatment effectiveness.
  7. Precipitate Analysis: Solids formed on the anode surface (identified as CaCO3 and CaO) were characterized using Thermogravimetry (TG) and Fourier Transform Infrared Spectroscopy (FTIR).

Commercial Applications

Section titled “Commercial Applications”

The electrochemical looping technology offers a sustainable pathway for industrial operations requiring both water treatment and clean energy generation.

  • Sustainable Green Hydrogen Production: Provides a viable, low-cost alternative to traditional water splitting, especially in regions facing water scarcity, by utilizing treated wastewater instead of clean water.
  • Industrial Wastewater Treatment: Applicable for the effective mineralization of low-concentration organic pollutants (like natural organic matter or industrial intermediates) using highly stable BDD/Nb anodes.
  • PV-Driven Energy Systems: Ideal for integration with decentralized solar energy infrastructure, supporting off-grid or remote industrial operations (SDG 7).
  • Electrochemical Reactor Design: Provides a blueprint for highly efficient, divided-cell reactors utilizing low-cost Ni-Fe SS mesh cathodes for high-volume H2 evolution.
  • Resource Recovery and Circular Economy: Facilitates the closure of the water loop in industrial processes by demonstrating the feasibility of reusing treated effluent for energy production.
  • BDD Electrode Supply: Confirms the long-term stability and effectiveness of BDD films supported on Niobium (Nb) for demanding, high-current density electrochemical applications.
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

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2022 - An Overview of Water Electrolysis Technologies for Green Hydrogen Production [Crossref]
  2. 2021 - Recent Development in Electrocatalysts for Hydrogen Production through Water Electrolysis [Crossref]
  3. 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]
  4. 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]
  5. 2024 - Energy-Saving Electrochemical Green Hydrogen Production Coupled with Persulfate or Hydrogen Peroxide Valorization at Boron-Doped Diamond Electrodes [Crossref]
  6. 2023 - A Sustainable Solar-Driven Electrochemical Process for Reforming Lignocellulosic Biomass Effluent into High Value-Added Products: Green Hydrogen, Carboxylic and Vanillic Acids [Crossref]
  7. 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]
  8. 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]

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