Unequal-ratio high-entropy spinel type proton ceramic fuel cell cathode material as well as preparation method and application thereof

Abstract

The invention discloses a non-equal-ratio high-entropy spinel type proton ceramic fuel cell cathode material as well as a preparation method and application thereof, the chemical formula of the cell cathode material is (MnFeCo) (3-x-y-z) / 3NixZnyCuzO4, 0 lt, 0 lt, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, xlt; 0.6, 0 lt; yt; Yt; 0 1t, 0.4, 0 1t; zlt, zlt; and 0.3. The preparation method comprises the following steps: weighing raw materials according to a stoichiometric ratio; 2, a metal precursor is dissolved in deionized water, ethylenediamine tetraacetic acid is dissolved with NH3.H2O, then the mixture is mixed with citric acid monohydrate, the pH value of the solution is adjusted to be 7-8, and the mixture is heated and stirred into a gel substance; drying the gelatinous substance to obtain a precursor; calcining the precursor at a high temperature of 750-850 DEG C; the invention also discloses an application of the ceramic fuel cell cathode material in a symmetric cell or a single cell. The synthesized material is in a single phase and does not contain other impurities, and all elements are uniformly distributed.

Description

Technical Field

[0001] The present invention relates to a cathode material, a preparation method and an application thereof, and specifically relates to a non-isotropic high-entropy spinel proton ceramic fuel cell cathode material, a preparation method and an application thereof. Background Art

[0002] Solid oxide fuel cells (SOFCs) are highly promising energy conversion devices. Their advantages include high efficiency, environmental friendliness, wide fuel compatibility, and the ability to achieve combined heat and power generation. Consequently, they exhibit broad application prospects in the energy sector and have become a key technology for promoting sustainable energy development. However, conventional oxygen-ion-conducting, high-temperature solid oxide fuel cells face numerous challenges in practical application. Their high-temperature operating conditions place stringent material requirements, resulting in high costs, long startup times, and poor thermal cycling performance, hindering their large-scale commercial application. Therefore, the development of medium-temperature SOFCs has become an inevitable trend.

[0003] Proton-conducting solid oxide fuel cells, or proton ceramic fuel cells (PCFCs), offer promise for the development of medium-temperature SOFCs. Their proton ceramic electrolytes exhibit sufficient conductivity at moderate temperatures (500-700°C), meeting the performance requirements for electrolytes operating at these temperatures. Furthermore, this moderate-temperature operation not only effectively reduces the battery's material requirements for high-temperature resistance, thus reducing material costs, but also shortens the battery's startup time and improves the system's thermal cycling stability, providing favorable conditions for the widespread application of fuel cells.

[0004] Although PCFCs offer significant advantages in operating at moderate temperatures, the cathode reaction kinetics slow as the operating temperature decreases, becoming a key factor limiting further improvements in battery performance. As the primary site of the oxygen reduction reaction (ORR), the cathode's reaction rate directly impacts the battery's output power and overall efficiency. Therefore, there is an urgent need to develop new, high-performance cathode materials that can operate at moderate temperatures to further enhance battery performance. Summary of the Invention

[0005] Purpose of the invention: In order to overcome the deficiencies in the prior art, the purpose of the present invention is to provide a non-isotropic high-entropy spinel proton ceramic fuel cell cathode material with high electrical conductivity. Another purpose of the present invention is to provide a low-cost and easy-to-operate method for preparing a non-isotropic high-entropy spinel proton ceramic fuel cell cathode material. Another purpose of the present invention is to provide an application of a non-isotropic high-entropy spinel proton ceramic fuel cell cathode material in a symmetrical cell or a single cell.

[0006] Technical solution: The present invention discloses a non-isotropic high entropy spinel proton ceramic fuel cell (PCFC) cathode material, whose chemical formula is (MnFeCo) (3-x-y-z) / 3 Ni x Zny Cu z O4, where 0 <x<0.6,0<y<0.4,0<z<0.3。

[0007] The method for preparing a cathode material of a non-isotropic high-entropy spinel-type proton ceramic fuel cell according to the present invention comprises the following steps:

[0008] Step 1: weighing a metal precursor, ethylenediaminetetraacetic acid, and citric acid monohydrate according to a stoichiometric ratio of metal cation: ethylenediaminetetraacetic acid: citric acid monohydrate of 1:0.5-2.5:1-3;

[0009] Step 2: dissolving the metal precursor in deionized water, dissolving EDTA in NH3·H2O, and then mixing them with citric acid monohydrate, adjusting the pH value of the solution to 7-8, and heating and stirring to form a gel-like substance;

[0010] Step 3, drying the gel-like substance to obtain a precursor;

[0011] Step 4: calcining the precursor at a high temperature of 750-850° C. to obtain a non-isotropic high-entropy spinel cathode material.

[0012] Furthermore, in step 1, the metal precursor is one or more of MnC4H6O4·4H2O, Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, C4H6O4Zn and Cu(NO3)2·3H2O.

[0013] Furthermore, in step 1, the molar number of the metal cation is the sum of the molar numbers of all metal ions.

[0014] Furthermore, in step 2, the temperature of heating and stirring is 80-100°C.

[0015] Furthermore, in step 2, the rotation speed of heating and stirring is 200-300 rpm.

[0016] Furthermore, in step three, the drying temperature is 200-300° C., and the drying time is 200-300 min.

[0017] Furthermore, in step 4, the high-temperature calcination time is 200-300 minutes.

[0018] The invention discloses an application of a non-isotropic high-entropy spinel proton ceramic fuel cell cathode material in a symmetrical cell or a single cell.

[0019] Furthermore, (MnFeCo) (3-x-y-z) / 3 Ni x Zn yCu z O4 as cathode, BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ For electrolytes.

[0020] Preparation Principle: High-entropy materials exhibit a complex and disordered atomic arrangement. This unique microstructure imparts four core effects: high entropy, severe lattice distortion, delayed diffusion, and cocktail effects, which correspond to the material's thermodynamic stability, structural properties, kinetic behavior, and performance, respectively. Through rational elemental composition design, these effects can be exploited to develop a range of advanced materials that meet specific target requirements. The non-isotropic high-entropy spinel design of the present invention leverages these effects, optimizing the elemental composition of traditional non-high-entropy spinels. By introducing multiple elements, including Mn, Fe, Co, Ni, Zn, and Cu, the high-entropy effect stabilizes the material structure. The severe lattice distortion of the high-entropy material increases the oxygen vacancy concentration and mobility, enhancing oxygen reduction reaction activity. Furthermore, the highly reducing, high-valent Mn and Co ions also enhance the oxygen reduction reaction rate. The delayed diffusion effect slows the migration of harmful elements at high temperatures, improving the cathode material's resistance to chromium poisoning in stacks using stainless steel interconnects and mitigating battery performance degradation. The high-entropy cathode material of the present invention effectively improves the surface oxygen reduction rate of the cathode material, improves the oxygen diffusion coefficient, and reduces the impedance of the traditional spinel cathode through reasonable high-entropy design, which has a positive promoting effect on improving the performance of PCFC.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0022] 1. Synthesis of non-isotropic high entropy spinel (MnFeCo) by a low-cost and easy-to-operate sol-gel method (3-x-y-z) / 3 Ni x Zn y Cu z O4 cathode material, the synthesized material is single-phase, does not contain other impurities, and the elements are evenly distributed;

[0023] 2. Obtained non-isotropic high entropy spinel (MnFeCo) (3-x-y-z) / 3 Ni x Zn y Cu z O4 exhibits higher electrical conductivity than conventional spinel;

[0024] 3. Obtained non-isotropic high entropy spinel (MnFeCo) (3-x-y-z) / 3 Ni x Zn y Cu zThe impedance of O4 as PCFC cathode material is lower than that of traditional spinel cathode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the XRD pattern of the MFCNZC non-isotropic high entropy spinel cathode material in Example 1 of the present invention;

[0026] Figure 2 This is an SEM-EDS image of the MFCNZC non-isotropic high entropy spinel cathode material in Example 1 of the present invention;

[0027] Figure 3 This is a comparison of the electrical conductivity of MCO spinel and MFCNZC non-isotropic high entropy spinel;

[0028] Figure 4 is the O-TPD diagram of MCO spinel and MFCNZC non-isotropic high entropy spinel;

[0029] Figure 5 This is a comparison of the AC impedance of MCO spinel and MFCNZC non-isotropic high-entropy spinel as symmetric battery cathodes at 550°C;

[0030] Figure 6 This is the performance diagram of a single cell with MFCNZC non-isotropic high entropy spinel as cathode, BZCYYb as electrolyte, and NiO-BZCYYb as anode. DETAILED DESCRIPTION

[0031] In the following embodiments, the method for preparing anode powder includes the following steps:

[0032] (1) Weigh 3.0 g of BZCYYb powder and 7.0 g of NiO powder, and use a measuring cylinder to measure 20 ml of anhydrous ethanol.

[0033] (2) The raw materials of step (1) were placed in a zirconia ball mill jar and then ball milled in a planetary ball mill for 4 h.

[0034] (3) The milled slurry was transferred to an agate mortar and manually ground until the ethanol was completely evaporated. The powder was then evenly spread on a Petri dish and dried in an oven at 60 °C for 5 h.

[0035] Example 1

[0036] A method for preparing a non-isotropic high-entropy spinel PCFC cathode material comprises the following steps:

[0037] (1) Weigh 3.3822 g of MnC4H6O4·4H2O, 5.5752 g of Fe(NO3)3·9H2O, 4.0160 g of Co(NO3)2·6H2O, 2.9709 g of Ni(NO3)2·6H2O, 0.9541 g of C4H6O4Zn, and 0.8214 g of Cu(NO3)2·3H2O and completely dissolve them in deionized water.

[0038] (2) Weigh 17.5344g of C 10 H 16 N2O8 and 25.2168g C6H8O7·H2O, use a graduated cylinder to measure 47ml NH3·H2O to 10 H 16 N2O8 dissolves. The molar ratio of metal cation: EDTA: citric acid monohydrate is 1:1:2.

[0039] (3) Combine the C6H8O7·H2O in step (2) and the C 10 H 16 N2O8 was added to the solution in step (1), and then the pH was adjusted to 7 with NH3·H2O.

[0040] (4) Stir the mixed solution at 300 rpm and a constant temperature of 80°C until it becomes a viscous gel.

[0041] (5) The obtained wet gel was placed in a forced air drying oven at 250°C and dried for 300 min to obtain a precursor.

[0042] (6) The precursor is placed in a muffle furnace and calcined at 800 °C for 300 min to obtain the desired non-isotropic high entropy spinel cathode material.

[0043] like Figure 1 The molecular formula of the non-isotropic high entropy spinel PCFC cathode material obtained in this embodiment is Mn 0.69 Fe 0.69 Co 0.69 Ni 0.5 Zn 0.26 Cu 0.17 O4, denoted as MFCNZC, its △S=1.766R.

[0044] like Figure 2 The elements (Mn, Fe, Co, Ni, Zn, Cu, O) of the non-isotropic high-entropy spinel PCFC cathode material are evenly distributed without any element aggregation phenomenon.

[0045] Example 2

[0046] A method for preparing a non-isotropic high-entropy spinel PCFC cathode material comprises the following steps:

[0047] (1) Weigh 3.3822 g of MnC4H6O4·4H2O, 5.5752 g of Fe(NO3)3·9H2O, 4.0160 g of Co(NO3)2·6H2O, 2.9709 g of Ni(NO3)2·6H2O, 0.9541 g of C4H6O4Zn, and 0.8214 g of Cu(NO3)2·3H2O and completely dissolve them in deionized water.

[0048] (2) Weigh 8.7672g of C 10 H 16 N2O8 and 12.6084g C6H8O7·H2O, use a graduated cylinder to measure 23ml NH3·H2O to 10 H 16 N2O8 dissolves. The molar ratio of metal cation: EDTA: citric acid monohydrate is 1:0.5:1.

[0049] (3) Combine the C6H8O7·H2O in step (2) and the C 10 H 16 N2O8 was added to the solution in step (1), and then the pH was adjusted to 7 with NH3·H2O.

[0050] (4) Stir the mixed solution at 200 rpm and a constant temperature of 90°C until it becomes a viscous gel.

[0051] (5) The obtained wet gel was placed in a forced air drying oven at 200°C and dried for 250 min to obtain a precursor.

[0052] (6) The precursor is placed in a muffle furnace and calcined at 850 °C for 200 min to obtain the desired non-isotropic high entropy spinel cathode material.

[0053] Example 3

[0054] A method for preparing a non-isotropic high-entropy spinel PCFC cathode material comprises the following steps:

[0055] (1) Weigh 3.3822 g of MnC4H6O4·4H2O, 5.5752 g of Fe(NO3)3·9H2O, 4.0160 g of Co(NO3)2·6H2O, 2.9709 g of Ni(NO3)2·6H2O, 0.9541 g of C4H6O4Zn, and 0.8214 g of Cu(NO3)2·3H2O and completely dissolve them in deionized water.

[0056] (2) Weigh 43.536g of C 10 H 16N2O8 and 37.8252 C6H8O7·H2O, use a graduated cylinder to measure 87ml NH3·H2O to 10 H 16 N2O8 dissolves. The molar ratio of metal cation: EDTA: citric acid monohydrate is 1:2.5:3.

[0057] (3) Combine the C6H8O7·H2O in step (2) and the C 10 H 16 N2O8 was added to the solution in step (1), and then the pH was adjusted to 8 with NH3·H2O.

[0058] (4) Stir the mixed solution at a speed of 250 rpm and a constant temperature of 100°C until it becomes a viscous gel.

[0059] (5) The obtained wet gel was placed in a 300°C forced air drying oven and dried for 200 min to obtain a precursor.

[0060] (6) The precursor is placed in a muffle furnace and calcined at 750 °C for 250 min to obtain the desired non-isotropic high entropy spinel cathode material.

[0061] Comparative Example 1

[0062] A method for preparing a conventional spinel PCFC cathode material MnCo2O4 is described. The remaining steps are the same as those in Example 1, except that step (1) is replaced by weighing 4.9018 g of MnC4H6O4·4H2O and 11.6412 g of Co(NO3)2·6H2O and completely dissolving them in deionized water.

[0063] The cathode materials obtained in Example 1 and Comparative Example 1 were tested for electrical conductivity performance.

[0064] A. Preparation of conductive strips, including the following steps:

[0065] (1) Take 1 g of cathode powder (MFCNZC in Example 1 or MnCoO in Comparative Example 1), mix it with an appropriate amount of polyvinyl alcohol (PVA), grind it until it is dry and fine without sticking to the wall, and place it on weighing paper for later use.

[0066] (2) The ground powder is placed in a specific mold and pressed at a pressure of 150 MPa for 1 min. After demolding, a rectangular strip of green embryo is obtained.

[0067] (3) The green body was placed in a muffle furnace and calcined at 1100°C for 5 h to obtain a dense strip sample.

[0068] B. Conductivity test

[0069] (1) Sample pretreatment: Silver paste was applied to both ends of the conductive strips made from the cathode materials of Example 1 and Comparative Example 1, and silver wires were connected as current contact points; conductive wires were fixed on both sides of the silver wires with conductive glue as voltage contact points.

[0070] (2) Test device construction: Connect the current wire and voltage wire of the sample to the current terminal and voltage terminal of the Keithley 2440 digital source meter respectively.

[0071] (3) Test conditions: A tube furnace was used for testing, and the test atmosphere was air; the test temperature range was 900°C to 300°C, the cooling rate was 5°C / min, and the interval between adjacent temperature points was 10°C; the program was controlled by LabVIEW software and data was automatically recorded.

[0072] (4) Test method: Apply a constant current to the sample to be tested and record the voltage value at both ends. Calculate the DC resistance according to Ohm's law: R=I / V, and then use the formula The conductivity σ of the sample is obtained.

[0073] like Figure 3 The conductivity of MFCNZC and MCO increases with increasing temperature. From 300 to 500°C, the conductivity increases of the two with increasing temperature are similar. Above 500°C, the conductivity increase of MFCNZC is greater than that of MCO. The maximum conductivities of MFCNZC and MCO are 46.069 S cm -1 and 15.853 S cm -1 .

[0074] like Figure 4 Before 480°C, the trends of the two curves are similar. Starting from 480°C, the curve of MnFeCoNiZnCuO begins to show an upward trend and reaches a peak at around 700°C, while the curve of MnCoO material begins to show an upward trend at 630°C and reaches a peak at around 900°C. The temperature of the peak of MnFeCoNiZnCuO is much lower than that of the peak of MnCoO material at 630°C, and it is clearly observed through area comparison that the peak area of ​​MnFeCoNiZnCuO material is much larger than the peak area of ​​MnCoO material.

[0075] Application Example 1

[0076] A method for preparing a symmetrical battery comprises the following steps:

[0077] S1. Preparation of cathode slurry

[0078] S1.1. Weigh 1 g of cathode powder (MFCNZC in Example 1 or MnCoO in Comparative Example 1), add 10 mL of isopropanol, 2 mL of ethylene glycol, and an appropriate amount of glycerol as dispersion medium, and place in a ball mill.

[0079] S1.2. Add an equal amount of water to another ball mill to balance the mixture and ensure a balanced ball milling process.

[0080] S1.3. Place the ball mill in a planetary ball mill, set the speed to 400 rpm, and ball mill for 1 h to obtain a uniform and stable cathode slurry.

[0081] Preparation of S2 and BZCYYb embryos

[0082] S2.1. Weigh 0.5 g of BZCYYb powder and place it in a special mold.

[0083] S2.2. Use a manual powder tablet press to press at constant pressure for 1 min to obtain a round green tablet with a diameter of about 15 mm.

[0084] S2.3. Place the green body in a muffle furnace and keep it at 1400℃ for 5 h to sinter it into a dense BZCYYb symmetrical battery matrix.

[0085] S3. Cathode coating and calcination

[0086] S3.1. Place the BZCYYb symmetrical battery matrix on a 200°C heating table for preheating.

[0087] S3.2. Use a spray gun to evenly spray the prepared cathode slurry on both sides of the substrate to ensure consistent coating thickness.

[0088] S3.3. After spraying, the sample was placed in a muffle furnace for calcination. The calcination conditions of the MnFeCoNiZnCuO and MnCoO cathode materials were 800 °C for 5 h, and finally a BZCYYb symmetrical battery cell was obtained.

[0089] Electrochemical impedance spectroscopy (EIS) testing includes the following steps:

[0090] (1) Apply silver paste on both sides of the symmetrical battery cell and connect silver wires as electrode leads.

[0091] (2) An electrochemical workstation was used to perform the electrochemical impedance spectroscopy (EIS) test. The test frequency range was 0.1 Hz to 1 MHz and the test temperature was 600-800 °C.

[0092] (3) The ohmic resistance and polarization resistance are obtained by Nyquist plot fitting to evaluate the electrochemical performance of the cathode material.

[0093] like Figure 5At 550℃, the impedance of the non-isotropic high-entropy MFCNZC cathode material is lower than that of the MCO cathode material, and the impedances of MCO and MFCNZC are 3.0 and 2.767, respectively.

[0094] Application Example 2

[0095] A method for preparing a single battery comprises the following steps:

[0096] S1. Preparation of anode layer:

[0097] S1.1. Weigh 0.35 g of anode powder and place it in a cylindrical mold with a diameter of 15 mm.

[0098] S1.2. After the powder is evenly spread, a manual tablet press is used to apply a pressure of 200 MPa and maintain it for 1 minute to obtain an anode green body.

[0099] S2. Preparation of electrolyte layer:

[0100] S2.1. Weigh 0.015 g of BZCYYb electrolyte powder;

[0101] S2.2. Evenly sieve the electrolyte powder onto the surface of the anode green body through a 200-mesh standard sieve.

[0102] S2.3. Apply a pressure of 400 MPa to the anode green sheet covered with the electrolyte layer and maintain the pressure for 1 minute to allow the two layers of material to be tightly bonded, thereby obtaining a green sheet with a double-layer structure.

[0103] S3, high temperature sintering process:

[0104] S3.1. Place the green sheet in a high-temperature muffle furnace;

[0105] S3.2. Raise the temperature to 900°C at a heating rate of 5°C / min.

[0106] S3.3. Keep warm for 5 hours and then cool in the furnace to obtain a half-cell.

[0107] S4. Preparation of cathode layer:

[0108] S4.1. Apply a high-temperature tape with 8 mm pores to the electrolyte layer of the half-cell.

[0109] S4.2. Weigh 1 g of MFCNZC powder and ball mill it with 10 ml of isopropanol, 2 ml of ethylene glycol, and 0.6 ml of glycerol for 2 h at a speed of 400 rpm to prepare the cathode slurry.

[0110] S4.3. Use a spray gun to evenly spray the cathode slurry (MFCNZC of Example 1 or MnCoO of Comparative Example 1) into a limited area of ​​0.48 cm².

[0111] S4.4. Place it in a muffle furnace and calcine at 800℃ for 5 hours to form a complete single cell.

[0112] test:

[0113] Silver paste is coated on the surfaces of the cathode and anode as current collectors, conductive glue is used to fix silver wires as current leads, and quartz tubes are used for airtight packaging.

[0114] like Figure 6 The open circuit voltage of the single cell with MFCNZC as cathode is close to 1 in the range of 600-700℃, and the peak power at 600-700℃ is 385, 267, and 186 mW cm, respectively. -2 , and the peak corresponding current density range is wide, and the power decay is relatively gentle, showing excellent power output capability and stability.

[0115] Among the above embodiments, the best embodiment is embodiment 1.

Claims

1. A non-isotropic high-entropy spinel proton ceramic fuel cell cathode material, characterized by: Its chemical formula is (MnFeCo) (3-x-y-z) / 3 Ni x Zn y Cu z O4, where 0 <x<0.6,0<y<0.4,0<z<0.3。 2. The method for preparing a cathode material for a non-isotropic high entropy spinel proton ceramic fuel cell according to claim 1, characterized in that: The following steps are involved: Step 1: weighing a metal precursor, ethylenediaminetetraacetic acid, and citric acid monohydrate according to a stoichiometric ratio of metal cation: ethylenediaminetetraacetic acid: citric acid monohydrate of 1:0.5-2.5:1-3; Step 2: dissolving the metal precursor in deionized water, dissolving EDTA in NH3·H2O, and then mixing them with citric acid monohydrate, adjusting the pH value of the solution to 7-8, and heating and stirring to form a gel-like substance; Step 3, drying the gel-like substance to obtain a precursor; Step 4: calcining the precursor at a high temperature of 750-850° C. to obtain a non-isotropic high-entropy spinel cathode material.

3. The method for preparing a cathode material for a non-isotropic high-entropy spinel proton ceramic fuel cell according to claim 2, characterized in that: In the step 1, the metal precursor is one or more of MnC4H6O4·4H2O, Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, C4H6O4Zn and Cu(NO3)2·3H2O.

4. The method for preparing a cathode material for a non-isotropic high-entropy spinel proton ceramic fuel cell according to claim 2, characterized in that: In the step 1, the molar number of the metal cation is the sum of the molar numbers of all metal ions.

5. The method for preparing a cathode material for a non-isotropic high-entropy spinel proton ceramic fuel cell according to claim 2, characterized in that: In the step 2, the temperature of heating and stirring is 80-100°C.

6. The method for preparing a cathode material for a non-isotropic high-entropy spinel proton ceramic fuel cell according to claim 2, characterized in that: In the step 2, the rotation speed of heating and stirring is 200-300 rpm.

7. The method for preparing a cathode material for a non-isotropic high entropy spinel proton ceramic fuel cell according to claim 2, characterized in that: In the step 3, the drying temperature is 200-300° C. and the drying time is 200-300 min.

8. The method for preparing a cathode material for a non-isotropic high-entropy spinel proton ceramic fuel cell according to claim 2, characterized in that: In the step 4, the high temperature calcination time is 200-300 minutes.

9. Use of the non-isotropic high-entropy spinel protonic ceramic fuel cell cathode material according to claim 1 in a symmetrical cell or a single cell.

10. The use of a non-isotropic high entropy spinel proton ceramic fuel cell cathode material according to claim 9 in a symmetrical cell or a single cell, characterized in that: (MnFeCo) (3-x-y-z) / 3 Ni x Zn y Cu z O4 as cathode, BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ For electrolytes.

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