Enhancement of the Catalytic Effect on the Electrochemical Conversion of CO2 to Formic Acid Using MXene (Ti3C2Tx)-Modified Boron-Doped Diamond Electrode

At a Glance

Metadata	Details
Publication Date	2023-06-06
Journal	Energies
Authors	Prastika Krisma Jiwanti, Asmaul Mashad Alfaza, Grandprix T.M. Kadja, Suci A.C. Natalya, Fuja Sagita
Institutions	Keio University, Airlangga University
Citations	12
Analysis	Full AI Review Included

Executive Summary

This analysis focuses on the development and performance evaluation of a novel electrode material system for the electrochemical reduction of carbon dioxide (eCO₂R) to Formic Acid (HCOOH).

Core Achievement: Successful modification of a Boron-Doped Diamond (BDD) electrode surface with MXene (Ti₃C₂T_x) nanosheets to enhance catalytic activity for CO₂ reduction.
Overpotential Reduction: The MXene modification significantly suppressed the high overpotential typically required for eCO₂R on bare BDD (literature value ~-2.2 V), achieving optimal performance at a potential as low as -1.3 V (vs. Ag/AgCl).
Optimal Performance: The highest concentration MXene electrode (MXene-BDD 2.0) yielded the maximum HCOOH concentration (28.9 ppm) and achieved a Faradaic Efficiency (FE) of approximately 97% at -1.3 V.
Catalytic Mechanism: The enhanced performance is attributed to MXene’s high surface area, excellent electrical conductivity, and the presence of highly electronegative terminal groups (-O and -OH) which facilitate CO₂ adsorption and reduction.
Stability Challenge: A major limitation was identified: the physically deposited MXene layer exhibited poor stability, showing a 79.9% decrease in material on the BDD surface after just 1 hour of operation at -1.7 V.

Technical Specifications

Parameter	Value	Unit	Context
Optimal Reduction Potential	-1.3	V (vs. Ag/AgCl)	MXene-BDD 2.0, highest FE
Maximum Faradaic Efficiency (FE)	~97	%	MXene-BDD 2.0 at -1.3 V
Highest HCOOH Concentration	28.9	ppm	MXene-BDD 2.0 (Calculated)
Bare BDD Reduction Potential	~-2.2	V (vs. Ag/AgCl)	Literature value for HCOOH production
Optimal MXene Concentration	2.0	mg/mL	MXene-BDD 2.0
Ti Weight Load (MXene-BDD 2.0)	7.14	%	EDX analysis
MXene Stability Loss (1 hr)	79.9	%	Decrease in MXene oxidation peak after reduction at -1.7 V
BDD Boron Doping Level	1	% (B/C)	Fabrication parameter
Cathode Electrolyte	0.5 M KCl	M	CO₂ reduction compartment
Anode Electrolyte	0.5 M KOH	M	Overpotential suppression
CO₂ Aeration Time (Optimal)	15	min	Achieved stable pH of 3.7
MXene XRD Main Peak	6	° (2θ)	Corresponds to (002) plane
MXene Raman D Band	1375	cm^-1	sp² carbon (perturbed)

Key Methodologies

The electrochemical reduction process utilized a two-compartment cell and a three-electrode system, focusing on material preparation, surface modification, and rigorous testing.

BDD Substrate Preparation: Polycrystalline BDD (1% B/C) was grown on a silicon wafer via Microwave Plasma-Assisted Chemical Vapor Deposition (MP-CVD).
BDD Pretreatment: The bare BDD surface was electrochemically cleaned using 40 cycles of Cyclic Voltammetry (CV) in 0.1 M H₂SO₄ (potential range: -2.5 V to +2.5 V).
MXene Synthesis: Ti₃C₂T_x MXene nanosheets were prepared using the standard LiF-HCl etching treatment.
Electrode Modification (Drop-Casting): MXene solutions were prepared at three concentrations (0.5, 1.0, and 2.0 mg/mL). 20 µL of the solution was drop-casted onto the BDD surface (0.754 cm² geometric area) and dried at room temperature.
Electrolyte and Cell Setup: A Nafion membrane separated the cathode (0.5 M KCl) and anode (0.5 M KOH) compartments. Electrodes used were modified BDD (Working), Pt spiral (Counter), and Ag/AgCl (Reference).
Gas Management: The cathode electrolyte was purged with N₂ for 10 minutes (to remove O₂), followed by 15 minutes of CO₂ aeration (to ensure saturation and stable pH 3.7).
Electrochemical Testing: Linear Sweep Voltammetry (LSV) was used for preliminary activity assessment. Chronoamperometry (CA) was performed for 1 hour at fixed potentials (-1.3 V, -1.5 V, and -1.7 V) to collect products.
Product Quantification: Formic Acid (HCOOH) yield was analyzed using High Performance Liquid Chromatography (HPLC).
Stability Assessment: CV was performed on the MXene-BDD 2.0 electrode before and after 1 hour of CO₂ reduction to quantify material loss.

Commercial Applications

This research contributes directly to the field of Carbon Capture and Utilization (CCU) and sustainable chemical manufacturing, leveraging the unique properties of diamond electrodes.

Sustainable Chemical Manufacturing: Direct electrochemical synthesis of high-value platform chemicals (like Formic Acid) from waste CO₂ streams, reducing reliance on fossil fuel feedstocks.
Carbon Capture and Utilization (CCU): Provides a viable, low-energy pathway for converting captured industrial CO₂ emissions into transportable and storable liquid products.
Energy Storage and Carriers: Formic Acid is a promising liquid organic hydrogen carrier (LOHC). This technology offers an efficient method for its production, supporting hydrogen economy infrastructure.
Advanced Electrocatalysis: The use of BDD as a stable, wide-potential-window substrate combined with 2D materials (MXene) provides a template for developing robust, high-performance electrodes for other complex multi-electron transfer reactions (e.g., nitrogen reduction, oxygen evolution).
Industrial Electrolyzers: The demonstrated low overpotential (down to -1.3 V) is critical for scaling up eCO₂R processes, as lower voltage requirements translate directly to reduced operational energy costs.

View Original Abstract

The rising concentration of carbon dioxide (CO2) as one of the greenhouse gases in the atmosphere is a major source of worry. Electrochemical reduction of CO2 is one of many ways to convert CO2 gas into usable compounds. An electrochemical technique was applied in this study to reduce CO2 using a boron-doped diamond (BDD) working electrode modified with MXene (Ti3C2Tx) material to improve electrode performance. MXene concentrations of 0.5 mg/mL (MXene-BDD 0.5), 1.0 mg/mL (MXene-BDD 1.0), and 2.0 mg/mL (MXene-BDD 2.0) were drop-casted onto the BDD surface. MXene was effectively deposited on top of the BDD surface, with Ti weight loads of 0.12%, 4.06%, and 7.14% on MXene-BDD 0.5, MXene-BDD 1.0, and MXene-BDD 2.0, respectively. The modified working electrode was employed for CO2 electroreduction with optimal CO2 gas aeration. The existence of the MXene substance in BDD reduced the electroreduction overpotential of CO2. For the final result, we found that the MXene-BDD 2.0 electrode effectively generated the most formic acid product with a maximum reduction potential as low as −1.3 V (vs. Ag/AgCl).

Tech Support

Original Source

DOI: https://doi.org/10.3390/en16124537

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