MXene modified CoZnCr for efficient water splitting from alkaline seawater and anion exchange membrane electrolyzer

MXene-assisted CoZnCr for efficient alkaline seawater splitting and anion exchange membrane electrolyzer Payal Chauhan1*, Prosun Santra2, Bing Wu1, Jan Plutnar1, Jakub Regner1, Alkesh B. Patel1, Martin Loula3, Mahdi Ghorbani-Asl2, Arkady V. Krasheninnikov2, Saeed Ashtiani1, Bahareh Khezri4,5,6, Zdeněk Sofer1* 1Department of Inorganic Chemistry, University of Chemistry and Technology Prague, Technická 5, Prague 6, 16628 Czech Republic 2Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum DresdenRossendorf, 01328 Dresden, Germany. 3Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 166 10 Prague 6, Czech Republic 4Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Marcel. lí Domingo 1, Tarragona 43007, Spain 5Institute of Chemical Research of Catalonia (ICIQ-CERCA), The Barcelona Institut of Science and Technology (BIST), Avinguda Països Catalans 16, Tarragona, 43007, Spain 6ICREA, Passeig Lluís Companys, 23, Barcelona, 08010, Spain Corresponding Authors: Zdenek Sofer, Email: [email protected] Payal Chauhan, Email: [email protected] Supplementary Information (SI) for Journal of Materials Chemistry A. This journal is © The Royal Society of Chemistry 2025 Preparation of Mo2TiC2 MXene In a high-density polyethylene beaker, 4 g of Mo2TiAlC2 Max phase was combined with aqueous concentrated HF. After that, the mixture was agitated for five days at 70 °C. The precipitation was washed with water several times. Further, the washed precipitation was mixed with 50 ml HF and stirred at 70 ◦C for another five days to remove aluminium. Deionized water was used to repeatedly wash the resultant suspension. Etched MXene was combined with 20 ml of TBAOH solution, and the mixture was swirled for 24 hours at room temperature. Ultimately, centrifugation in deionized water was used to gather the products. Computational Details Density functional theory (DFT) calculations were performed using a plane-wave basis set with the projector-augmented wave (PAW) method, as implemented in the VASP code. 1,2 The generalized gradient approximation (GGA) with the PBE exchange-correlation functional3 was employed for all the calculations. Was used. Van der Waals interactions were considered using the DFT-D2 method proposed by Grimme.4 A plane-wave cut-off energy of 400 eV and force tolerance of 0.01 eV/Å was set for geometry optimization. To model the slabs, a vacuum space of approximately 40 Å was introduced between the heterostructures in the confinement direction. A 5×5 supercell was employed for simulations of intermediate adsorptions on the LDH. The adsorption energy of the adsorbate on the surface was calculated as follows, Eads = Eslab+adsorbate − Eslab − Eadsorbate (1) where the Eslab+adsorbate represents the total energy of the slab with adsorbate, Eslab indicates the energy of the isolated slab, and Eadsorbate stands for the energy of the isolated adsorbate. Hydrogen evolution reaction (HER) The HER performance of the systems can be characterized by the Gibbs free reaction energy Δ𝐺, according to the following equation: Δ𝐺 = Δ𝐸𝑎𝑑𝑠 + Δ𝐸𝑍𝑃𝐸 − 𝑇Δ𝑆 (2) ΔEads indicates the change in the internal energy, Δ𝐸𝑍𝑃𝐸 denotes the change in the vibrational zero-point energy, and ΔS stands for the difference in entropy. In the case of hydrogen adsorption, the term ∆EZPE - T∆SH can be estimated to be +0.24 eV at room temperature, as shown previously.1, 2, 3 As a result, Equation 2 can be simplified to ∆GH = ∆EH + 0.24 eV. Oxygen evolution reaction (OER) The OER reaction operates via a four-electron mechanism that consists of four fundamental steps. These steps involve the adsorption of intermediates such as OH, O, and OOH on the surface (*) as follows: I) * + OH- *OH + e- (3) II) *OH + OHH2O + *O + e- (4) III) *O + OH- *OOH + e- (5) IV) *OOH + OHO2 + H2O + e- (6) According to the computational hydrogen electrode (CHE) model, the reaction free energy of equations for OER can be calculated using the following equations: ΔGI = ΔGOH* (7) ΔGII = ΔGO* - ΔGOH* (8) ΔGIII = ΔGOOH* - ΔGO* (9) ΔGIV = 4.92 - ΔGOOH* (10) Where ΔGO*, ΔGOH* and ΔGOOH* correspond to the free energy changes associated with the adsorption of O, OH, OOH, respectively. The total energy change of the system during the OER process corresponds to 4.92 eV at 1.23 V. Thus, the theoretical overpotential (η), which reflects the catalytic activity of the material, can be calculated as follows: η = max[ΔGI, ΔGII, ΔGIII, ΔGIV ] / e - 1.23 V Supplementary Fig. 1: a XRD pattern of ZIF-67, CoZnCr LDH and CoZnCr@Mo2TiC2 MXene. b XRD pattern of Mo2TiC2 MXene. Supplementary Fig. 2: XPS spectrum. a Zn 2p, b Cr 2p, c Mo 3d d o1s e C 1s. Supplementary Fig. 3. a. Linear sweep voltammetry (LSV) curves for the HER at industrial current density. b. EIS of various electrocatalyst in alkaline electrolyte. Supplementary Fig. 4. Cyclic voltammetry of a. CoZnCr@MXene. b. CoZnCr. c. MXene at various scan rates. d. Plots of current density vs different scan rates with calculated Cdl. Supplementary Fig. 5. Overpotential at different pH range in CoZnCr@MXene. Supplementary Fig. 6. Comparison of cell voltage of various electrocatalysts at 10 mA cm-2. Supplementary Fig. 7. a. OWS of Pt/c||RuO2 in natural seawater. b. LSV of CoZnCr@MXene in various electrolytes for HER. c. LSV of CoZnCr@MXene in various electrolytes for OER. d. OWS of Pt/c||RuO2 at various temperature. Supplementary Fig. 8. a. SEM image of CoZnCr@MXene after cycling. b. XRD pattern of CoZnCr@MXene after and before cycling. c. XPS of CoZnCr@MXene initial and after OER stability. Supplementary Fig. 9. Atomic structure of a. Mo2TiC2 and b. CoZnCr. Supplementary Fig. 10. Electronic structures and projected density of states (PDOS) of different structural models (a-b) Mo2TiC2O2, (c-d) Mo2TiC2(OH)2, (e-f) Mo2TiC2F2 Supplementary Fig. 11. Density state analysis. Calculated density of states for CoZnCr and MXene in different structural models a. CoZnCrO4H /Mo2TiC2(OH)2, b. CoZnCrO4H /Mo2TiC2F2. Supplementary Fig. 12. a. Image of overall water splitting of CoZnCr@MXene electrolyzer by a drainage method. b. Measured and calculated volumes of O2 in 1M KOH+seawater electrolyte. c. cell efficiency of CoZnCr@MXene based AEM electrolyzer comparted with DOE target value. Supplementary Table S1: A comparison of the OER overpotential and Tafel at current density in an alkaline electrolyte with reported electrocatalysts. Catalyst Overpotential (mV) Tafel slope (mV dec-1) Current density (mA cm-2) Electrolyte s Reference CoZnCr@MXene 20 54 10 1M KOH This work CoZnCr@MXene 180 - 50 1M KOH This work FeNi-V2C 250 46.5 10 1M KOH 4 Fe-NiFe 220 47.3 10 1M KOH 5 NiFeCr 225 69 25 1M KOH 6 CoFe-Ni2P 200 36.1 10 1M KOH 7 NiMoN@NiFeN 277 58.6 100 1M KOH 8 NiFe/Fe-MoO2 213 48 20 1M KOH 9 NiFeCo-Ni 137 23 10 1M KOH 10