Amphoteric Membrane Loaded with a Noble Metal-Free Hollow Spherical NiCoP@rGO Bifunctional Electrocatalyst for Alkaline Water Electrolyzers

Abstract

For overall water splitting and simultaneous hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) processes in alkaline media, a bifunctional electrocatalyst loaded on both surfaces of an amphoteric ion exchange membrane (AIEM) was conceptualized to improve the efficiency. Herein, we report a partially fluorinated polymer (poly(vinylidene fluoride-co-hexafluoropropylene))-based AIEM grafted with sulfonic acid and quaternary amine functional groups. The prepared AIEM was utilized as a substrate for the loading of the electrocatalyst (hollow spherical NiCoP@rGO) to prepare a membrane electrode assembly. The morphology-dependent bifunctional performance of the NiCoP@rGO electrocatalyst was assessed for overall water splitting (HER and OER). The prepared electrocatalyst exhibited a low potential (0.297 V for the HER and 1.57 V for the OER) at 10.00 mA/cm 2 current density, corresponding to 129 and 110 mV/dec Tafel slopes, respectively. Thus, the prepared MEA exhibited better overall water splitting performance in comparison to other commercialized membrane substrates and reported electrocatalysts in the literature, at 30 °C under 400 mA/cm 2 in alkaline medium (1.0 M KOH). A stable fluorinated polymer-based AIEM and hollow spherical NiCoP@rGO electrocatalyst provide a significant improvement in water electrolysis and simultaneous H 2 and O 2 production via HER and OER processes.

Key components and design strategy of the membrane electrode assembly for alkaline water electrolysis

“…At present, the commercial Zirfon PERL composite membrane has been successfully used in alkaline liquid water electrolysis, which consists of hydrophilic ZrO 2 nanoparticles (85 wt%) and a polysulfone backbone with an average pore size of 150 nm. There are two regions in the porous Zirfon PERL membrane: (1) interconnected ZrO 2 pores (B30 nm); 165 2, 164 3, 166 4, 167 5, 168 6, 163 7, 169 8, 170 9, 39 10 151 , 11, 171 12, 172 13, 19 14, 173 15, 174 16, 69 17, 175 18, 176 19, 51 20, 177 21, 178 22, 179 23, 26 24, 180 25, 181 26, 182 27, 183 28, 67 29, 184 30, 185 31, 186 32, 74 33, 187 34, 29 35, 46 36, 36 37, 188 38, 189 39, 190 40, 54 41, 191 42, 192 43, 27 44, 47 45, 34 46, 193 47, 76 48, 49 49, 68…”

“…(d) Electrolysis performance of representative alkaline water electrolysis fed with 0.1 M KOH or pure water. References for data points for (a): 1,165 2,164 3, 166 4,167 5,168 6,163 7,169 8,170 9, 39 10 151 , 11,171 12,172 13,19 14,173 15,174 16,69 17,175 18,176 19,51 20,177 21,178 22,179 23,26 24,180 25,181 26,182 27,183 28,67 29,184 30,185 31,186 32,74 33,187 34,29 35,46 36,36 37,188 38,189 39,190 40,54 41,191 42,192 43,27 44,47 45,34 46,193 47,76 48,49 49,68 50,194 51,38 52,52 53,…”

“…(b): 1,27 2,47 3, 32 4,34 5,194 6,38 7,52 8,62 9,195 10 44 , 11,45 12,28 13,30 14,35 15,82 16,60 17,196 18,197 19,37 20,198 21,62 22,199 23,84 24,63 25,64 26,200 27,43 28,65 29,57 30,33 31,48 32,201 33,202 34,72 35,56 36,203 37,33 38 70. (c): 1,26 2,180 3,204 4,93 5,205 6,54 7,206 8,86 9,207 10,183 11,74 12,29 13,208 14,181 15,184 16,…”

“…Fig.15(a) Degradation rates during continuous long-term durability testing of the reported alkaline water electrolysis. References for data points for (a): 1,26 2,84 3, 28 4,35 5,183 6,74 7,29 8,31 9,32 10 194 , 11,67 12,186 13,203 14,36 15,192 16,191 17,180 18,54 19,79 20,258 21,34 22,45 23,77 24,38 25,27 26,47 27,83 28,52 29,188 30,189 31,94 32,259 33,78 34,60 35,196 36,41 37,62 38,49 39,53 40,63 41 70. The degradation pathway of (b) QA and (c) IM groups under alkaline conditions 260.…”

“…17(a) Recent research on MEA preparation technologies including CCS with ionomer, CCM, and CCS with a self-supported electrode: (a) the current density of MEAs at a cell voltage of 1.8 V in 1 M KOH. References for data points for CCS with ionomer: 1 (Ir black//Aemiont//Pt/C); 225 2 (Cu 0.5 Co 2.5 O 4 //X37-50 Grade T//Pt/C); 44 3 (NiFe 2 O 4 //A201//NiFeCo); 33 4 (NiFe LDH//X37-50//Pt/C); 49 5 (IrO 2 //HTMA-DAPP//Pt/C); 210 6 (Ir black// Fumapem-3-PE-30//NiCu MMO); 215 7 (Co//PFAEM//Pt/C); 208 8 (CuCoO//X37-50 Grade T//NiCoO-NiCo/C); 32 9 (Ni 2 Fe 1 B//Fumapem-3-PE-30//Pt/ C); 259 10 (CoCuO//QPC-TMA//Pt/C); 94 11 (IrO 2 /FAA-3//Pt/C); 200 12 (NiFeO x //FAA-3-50//Pt/C); 43 13 (Ni(OH) 2 -Fe//Sustainion XA-9//RANEY s NiMo); 48 14 (NiS 2 /Ni 3 S 4 //FAA-3-50//Pt/C); 63 15 (Pt/C//QPAP//Pt/C); 181 16 (IrO 2 //PDTP//Pt/C); 184 17 (NiCo 2 O 4 @C//X37-50 Grade T//NiCo 2 O 4 @C); 27 18 (NiFe 2 O 4 // C-IL-100//NiFeCo), 36 CCM: 1 (IrO 2 //QPC-TMA//Pt/C); 190 2 (IrO 2 //PFOTFPh-TMA//Pt/C); 191 3 (NiMnO x //FAA-3-50//Pt/C); 30 4 (Ir black//A201//Ni-W-600); 72 5 (IrO 2 //QMter-co-Mpi//Pt/C); 192 6 (IrO 2 //A201//Pt/C); 201 7 (IrO 2 //PTP-C1//PtRu/C); 185 8 (IrO 2 //TM1t//Pt/C); 188 9 (IrO 2 //FAA-3-50//Pt/C), 196 10 (NiFe//FAA-3-50//Pt/C); 197 11 (IrO 2 //FAA-3-50//Pt/C); 200 12 (IrO 2 //PBB-SEBS//Pt/C); 182 13 (IrO 2 //QAPPT/LDH//Pt/C); 189 14 (IrO 2 //PFPB-QA//Pt/C);187 15 (NiCoP@rGO//AIEM//NiCoP@rGO),74 and CCS with a self-supported electrode: 1 (Cu 0.81 Co 2.19 O 4 //X37-50//Co 3 S 4 );31 2 (CuCo 2 O 4 //X37-50 Grade T// Pt/C); 38 3 (CuCoO//X37-50 Grade T//Pt/C); 45 4 (NiFe 2 O 4 //X37-50//RANEY s Ni); 41 5 (NiFeV LDH//X37-50 Grade T//Pt/C); 52 6 (NiFeOOH//FAA-3-50//Pt/ C); 57 7 (Ni 0.75 Fe 2.25 O 4 //X37-50 Grade T//Pt/C); 34 8 (FeNi-PS//FAA-3-50//FeNi-PS); 82 9 (NiFeCo LDH//X37-50 Grade T//NiFeCoP); 47 10 (NiFe LDH/MoS x // FAA-3-50//Pt/C); 65 11 (Co(OH) x -Ag-Co(OH) 2 //X37-50//Pt/C); 55 12 (IrO 2 //X37-50//CuCoP); 76 13 (CoSb 2 O 6 //FAA-3-50//Pt/C); 37 14 (Ni foam//PVBC-MPy/PSF//Ni foam); 180 15 (Ni 2 Fe 8 -Ni 3 S 2 //FAA-3-50//Ni 4 Mo/MoO 2 ); 62 16 (Ir-Ni/Mo 5 N 6 //X37-50 Grade T//Ir-Ni/Mo 5 N 6 );194 17 (Ni 2 P@FePO x H y //X37-50// NiMoO 4 );193 18 (IrO 2 //X 37-50//Ni@Ni(OH) 2 );68 19 (Fe 2 P-Ni 12 P 5 //FAA-3-50//Co 2 P-Ni 12 P 5 ); 80 20 (NiCoP//X37-50 Grade T//Pt/C);195 21 (NiFeCr LDH// X37-FA//NiMoCo);53 22 (Fe-CoOOH//X37-50//Pt/C);50 23 (NiCoP@NiFeP//FAA-PK-130//NiCoP@NiFeP);78 24 (S-FeOOH//FAA-3-50//Pt mesh);60 25 (NiFe//FAA-3-PE-30//NiFeP) 79. Schematic of conventional MEA preparation methods with ionomers: (b) CCS and (c) CCM methods 276.…”