Method for producing hydrogen by directly electrolyzing seawater and effectively inhibiting precipitation

Abstract

The invention provides a method for producing hydrogen by directly electrolyzing seawater, which can effectively inhibit precipitation. Natural seawater is used as an electrolyte, alternating current is applied to an electrode, and the polarity of the electrode is periodically and alternately converted between a cathode state and an anode state by utilizing the periodic change of the voltage of the alternating current; oH <-> generated by a hydrogen evolution reaction in a cathode state is consumed to inhibit precipitation and reduction of the catalytic activity of the electrode. The invention also provides a method for producing hydrogen by electrolyzing the solution capable of generating the precipitate under the alkaline condition.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolysis of seawater, and specifically comprises a method for producing hydrogen by direct electrolysis of seawater which can effectively inhibit precipitation. Background Art

[0002] As the first choice to meet energy needs in the future, hydrogen energy has the advantages of high combustion calorific value, clean and pollution-free, environmentally friendly, and convenient transportation. The sources of hydrogen are mainly fossil fuel hydrogen production, industrial by-product hydrogen production, and water electrolysis hydrogen production. Among them, fossil fuel hydrogen production and industrial by-product hydrogen production have limited raw material reserves and high carbon emissions in the hydrogen production process, which does not meet the "dual carbon" goals. There is no greenhouse gas emission in the entire process of hydrogen production by electrolysis of water, and the produced hydrogen is of high purity, so it is the main development direction in the future. Considering the scarcity of fresh water, as the global demand for hydrogen increases dramatically, it will be more promising to produce hydrogen with abundant seawater resources (accounting for 96.5% of the world's total water). In the process of direct electrolysis of seawater to produce hydrogen, a hydrogen evolution reaction occurs at the cathode to produce hydrogen, and at the same time, hydroxide ions (OH - ). OH accumulated on the cathode surface - The Mg present in large quantities in natural seawater 2+ and Ca 2+ Combined with other materials, Mg(OH)2 and Ca(OH)2 precipitates are produced around the cathode. These insoluble precipitates physically block the active sites of the catalyst, leading to catalyst deactivation, clogging of the diaphragm, increasing the ohmic loss of the electrolyzer, and deteriorating the long-term stability of the electrode performance. It is reported that these insoluble precipitates cover the cathode surface and reduce the current density of seawater electrolysis by 50%. Therefore, the generation of insoluble precipitates during the H2 production process, which leads to catalyst deactivation and performance degradation, is a key issue that needs to be urgently addressed in the direct electrolysis of seawater to produce H2.

[0003] There are currently three strategies to eliminate or mitigate the generation of insoluble precipitates during H2 production by electrolysis of seawater. (1) Seawater pretreatment. Precipitation of Mg by adding KOH / NaOH to natural seawater or by pre-electrocatalytic process 2+ and Ca 2+ , and then removed by filtration. Although effective, the high prices of KOH and NaOH and the complexity of the pretreatment process will greatly increase the cost of H2 production. (2) Equipment improvement. By using a selective permeable membrane to prevent unfavorable ions from entering the reaction system from seawater, precipitation is hindered or reduced, which requires additional costs related to membrane replacement and equipment maintenance. (3) Electrocatalyst improvement. A research team introduced a Lewis acid layer (Cr2O3) on the surface of the transition metal oxide catalyst, using the Lewis acid layer to react with OH in the double layer on the anode surface. - The strong binding of OH - and Mg 2+ , Ca2+ However, the Lewis acid layer and OH - The binding capacity of α-D-type ...

[0004] Although great progress has been made, current methods either cannot completely solve the precipitation problem in the process of producing H2 by seawater electrolysis, or significantly increase the cost of H2 production due to the use of specialized equipment and complex processes. Therefore, developing more effective and lower-cost strategies to solve the precipitation problem in the process of direct seawater electrolysis is of great significance for direct seawater electrolysis to produce hydrogen. Summary of the invention

[0005] In view of the above problems existing in the prior art, the present invention aims to provide a method for producing hydrogen by direct electrolysis of seawater which effectively inhibits precipitation. The method utilizes the periodic change of alternating current to timely eliminate the OH generated by the electrode in the cathode state. - , avoiding the precipitation of calcium and magnesium ions on the electrode surface, thereby ensuring the long-term reaction activity of the electrode and increasing the service life of the electrode.

[0006] Due to the periodic change of the AC voltage, the polarity of the electrode will be switched alternately between the cathode state and the anode state. In the present invention, for the same electrode, the cathode state refers to the electrode as a cathode to perform hydrogen evolution reaction at this moment voltage, and the anode state refers to the electrode as an anode to perform oxygen evolution reaction and / or chlorine oxidation reaction at this moment voltage. Further, the anode state refers to the electrode as an anode to perform electrochemical oxidation reaction at this moment voltage, including but not limited to oxygen evolution reaction and / or chlorine oxidation reaction.

[0007] To achieve the above object, the technical solution adopted by the present invention includes:

[0008] The present invention discloses a method for effectively inhibiting precipitation in the process of direct electrolysis of seawater for hydrogen production. Natural seawater is used as electrolyte, alternating current is applied to electrodes, and the polarity of the electrodes is periodically switched between cathode state and anode state by utilizing the periodic change of the voltage of the alternating current. When the electrodes are in the anode state, OH generated by hydrogen evolution reaction in the cathode state is consumed. - To inhibit precipitation and the decrease of electrode catalytic activity.

[0009] Since seawater is rich in calcium and magnesium ions, if direct current is used to electrolyze seawater to produce hydrogen, OH generated on the cathode surface during the hydrogen evolution reaction will - Mg in seawater 2+ and Ca 2+The insoluble precipitate is formed and covers the electrode surface, causing a series of problems such as catalyst deactivation, increased ohmic loss, and reduced electrode stability. The catalytic activity of the electrode is difficult to maintain for a long time. To this end, the present invention provides a simple treatment method, which cleverly utilizes the periodic change of alternating current. By controlling the waveform, voltage and period of alternating current, the electrode is periodically switched between the cathode state and the anode state. When the electrode is in the cathode state, a hydrogen evolution reaction occurs near the electrode to produce hydrogen and OH - When the electrode is converted to the anode state, oxygen evolution reaction and / or chlorine oxidation reaction occur near the electrode, consuming the OH generated in the cathode state. - , thereby eliminating the OH produced by the electrode in the cathode state - .

[0010] Furthermore, in the present invention, the reactions occurring near the electrode are as follows:

[0011] When the electrode is in the cathode state: 2H2O+2e - →H2↑+2OH -

[0012] When the electrode is in the anode state: 4OH - →O2↑+2H2O+4e -

[0013] Or Cl - +2OH - →ClO - +H2O+2e -

[0014] Furthermore, the waveform of the alternating current is selected from a square wave, a sine wave or a triangle wave; preferably a square wave.

[0015] Further, the voltage of the alternating current is 1.8-4V; illustratively, the voltage of the alternating current may be 1.8V, 2V, 2.2V, 2.4V, 2.6V, 2.8V, 3V, 3.2V, 3.4V, 3.6V, 3.8V, 4V, etc.

[0016] Further, the cycle of the alternating current is 0.01-2s; illustratively, the cycle of the alternating current can be 0.01s, 0.02s, 0.05s, 0.1s, 0.2s, 0.5s, 0.8s, 1s, 1.2s, 1.5s, 1.8s, 2s, etc.

[0017] It should be noted that the present invention does not make any specific limitation on the electrode material. Electrode materials commonly used by technicians in this field can be used in this method. They can be loaded electrodes or unloaded electrodes. At the same time, the present invention does not make any specific limitation on the source of the electrode material. It can be a commercially available electrode or an electrode prepared by itself with reference to the disclosed preparation method, all of which are within the protection scope of the present invention. Exemplarily, the electrode is selected from one of RuO2@nickel foam electrode, nickel foam electrode, nickel sheet electrode, platinum electrode, platinum-rhodium alloy electrode, graphite electrode, titanium electrode, titanium foam electrode, carbon paper electrode, and graphene electrode.

[0018] Furthermore, the precipitate is Ca(OH)2 and Mg(OH)2.

[0019] Further, the temperature of the electrolyte is 5-95°C; illustratively, it can be 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C,

[0020] 90℃, 95℃, etc.

[0021] Further, the voltage of the alternating current is 1.2-380V; illustratively, the voltage of the alternating current is 1.2V, 1.5V, 5V, 10V, 50V, 100V, 220V, 380V, etc. Preferably, the voltage of the alternating current is 1.2-1.8V. Preferably, the voltage of the alternating current is 1.8-4V. Preferably, the voltage of the alternating current is 4-380V.

[0022] Further, the cycle of the alternating current is 0.001-2s; illustratively, the cycle of the alternating current is 0.001s, 0.002s, 0.003s, 0.004s, 0.005s, 0.006s, 0.007s, 0.008s, 0.009s, etc. Preferably, the cycle of the alternating current is 0.001-0.01s. Preferably, the cycle of the alternating current is 0.01-2s.

[0023] It should be noted that the present invention does not specifically limit the source of seawater, and natural seawater from any region on Earth can be used directly in the electrolytic hydrogen production reaction without the need for additional operations such as removal of calcium and magnesium ions.

[0024] According to another aspect of the present invention, the present invention also provides a method for producing hydrogen by electrolysis of a solution that generates a precipitate under alkaline conditions, using a solution that generates a precipitate under alkaline conditions other than natural seawater as an electrolyte, applying alternating current to the electrodes, and utilizing the periodic change of the alternating current voltage to periodically switch the polarity of the electrodes between the cathode state and the anode state, and when the electrodes are in the anode state, OH generated by the hydrogen evolution reaction in the cathode state is consumed. - To inhibit precipitation and decrease in electrode catalytic activity;

[0025] The other solutions that generate precipitates under alkaline conditions include solutions containing ions that can be precipitated under alkaline conditions.

[0026] The solution that generates precipitation under alkaline conditions refers to a solution containing ions (such as Ca 2+ Mg 2+ When the solution is alkaline, these ions react with OH - The alkaline condition refers to the pH of the solution being greater than 7.

[0027] Preferably, the other solution that generates a precipitate under alkaline conditions is selected from a solution containing Ca 2+ Solutions and / or containing Mg 2+ of solution.

[0028] Preferably, the other solution that generates precipitation under alkaline conditions is selected from any one or more of the following: river water, salt lake water, mine water, industrial wastewater, and domestic sewage.

[0029] Preferably, the Ca 2+ and / or Mg 2+ The solution is selected from any one or more of the following: river water, salt lake water, mine water, industrial waste water, and domestic sewage.

[0030] Preferably, the cycle of the alternating current is 0.001-2s.

[0031] Preferably, the period of the alternating current is 0.001-0.01s.

[0032] Preferably, the period of the alternating current is 0.01-2s.

[0033] Preferably, the voltage of the alternating current is 1.2-380V.

[0034] Preferably, the voltage of the alternating current is 1.2-1.8V.

[0035] Preferably, the voltage of the alternating current is 1.8-4V.

[0036] Preferably, the voltage of the alternating current is 4-380V.

[0037] Furthermore, the waveform of the alternating current is selected from a square wave, a sine wave or a triangle wave.

[0038] Preferably, the waveform of the alternating current is selected from a square wave.

[0039] Furthermore, the electrode is selected from one of RuO2@nickel foam electrode, nickel foam electrode, nickel sheet electrode, platinum electrode, platinum-rhodium alloy electrode, graphite electrode, titanium electrode, titanium foam electrode, carbon paper electrode and graphene electrode.

[0040] Furthermore, the temperature of the electrolyte is 5-95°C.

[0041] Beneficial effects of the present invention:

[0042] In order to solve the problems of catalyst deactivation, increased ohmic loss, reduced electrode stability, etc. in direct current electrolysis of seawater for hydrogen production, the present invention proposes a technology for direct seawater electrolysis for hydrogen production using alternating current. By utilizing the periodic changes of alternating current, the OH generated by the hydrogen evolution reaction can be consumed in situ and in real time. - , avoiding the precipitation of calcium and magnesium ions on the electrode surface, and at the same time achieving the purpose of long-term electrolysis of seawater to produce hydrogen, greatly improving the efficiency of direct electrolysis of seawater to produce hydrogen and the service life of the electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0044] Figure 1 Schematic diagram of the principle of producing hydrogen by electrolyzing seawater with alternating current of the present invention.

[0045] Figure 2 A schematic diagram showing the square waveform AC input applied in Example 1.

[0046] Figure 3 The effect diagram before and after the electrolysis of seawater using square waveform alternating current in Example 1 is shown.

[0047] Figure 4 The current density-time curve of the electrolysis of seawater using square waveform alternating current in Example 1 is shown.

[0048] Figure 5 The gas chromatogram of gaseous products of seawater electrolysis by square wave alternating current in Example 1 is shown.

[0049] Figure 6 A graph showing the hydrogen evolution efficiency of electrolyzing seawater using square waveform alternating current of different periods in Examples 1-4.

[0050] Figure 7A schematic diagram showing the sinusoidal wave AC power input applied in Example 5.

[0051] Figure 8 A schematic diagram showing the triangular wave AC power input applied in Example 6.

[0052] Fig. 9 The effect diagram before and after using direct current to electrolyze seawater in Comparative Example 1 is shown.

[0053] Fig.10 A current density-time curve diagram of the electrolysis of seawater using direct current in Comparative Example 1 is shown.

[0054] Fig.11 Example 19 shows that the Figure 1 The curve shown is the voltage of the sinusoidal alternating current on the two electrodes varying with time (one period T), and the data is recorded by an oscilloscope.

[0055] Fig.12 The curve of current density changing with time in Example 19 is shown.

[0056] Fig.13 The curve of current density changing with time in one cycle in Example 19 is shown.

[0057] Fig.14 Example 23 shows that the Figure 1 The curve shown is the voltage of the triangular wave alternating current on the two electrodes changing with time (one period T), and the data is recorded by an oscilloscope.

[0058] Fig.15 The curve of current density changing with time in Example 23 is shown.

[0059] Fig.16 The curve of current density changing with time in one cycle in Example 23 is shown. DETAILED DESCRIPTION

[0060] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and drawings. It should be clear that the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] In addition, unless otherwise specified, the raw materials used in the present invention can be obtained commercially, and any range recorded in the present invention includes the end value and any numerical value between the end values ​​and any sub-range formed by the end value or any numerical value between the end values.

[0062] Example 1

[0063] See also Figure 1 , natural seawater was used as the electrolyte, RuO2@ nickel foam electrodes were used as the two electrodes, and square waveform alternating current ( Figure 2 ) was used as a power source to electrolyze natural seawater, the voltages Ea (anode voltage) and Ec (cathode voltage) were 1.8 V and -1.8 V respectively, the period T was 1 s, and the electrolyte temperature was room temperature (25 °C).

[0064] During the electrolysis process, bubbles were observed to continuously form on both electrodes, and no precipitation was formed on the electrode surface after 40 min of electrolysis ( Figure 3 , Figure 3 The left picture is the picture before AC electrolysis, and the right picture is the picture after AC electrolysis). The current is stable during this process ( Figure 4 The generated gas was collected by drainage method and analyzed by high performance gas chromatography, and the collected gas was pure hydrogen ( Figure 5 ).

[0065] Figure 6 The changes in hydrogen evolution during continuous electrolysis for 100 min were monitored, and the maximum hydrogen evolution efficiency reached 76.01%, and the hydrogen evolution efficiency was 58.55% at the end of electrolysis.

[0066] Example 2

[0067] See also Figure 1 , natural seawater was used as the electrolyte, RuO2@ nickel foam electrodes were used as the two electrodes, and square waveform alternating current ( Figure 2 ) was used as a power source to electrolyze natural seawater. The voltages Ea (anode voltage) and Ec (cathode voltage) were 1.8 V and -1.8 V respectively. The period T was 2 s and the electrolyte temperature was room temperature (25 °C).

[0068] During the electrolysis process, bubbles were observed to be continuously generated on both electrodes without precipitation, and the current was stable during the process.

[0069] Figure 6 The changes in hydrogen evolution during continuous electrolysis for 60 min were monitored, and the highest hydrogen evolution efficiency reached 78.45%.

[0070] Example 3

[0071] See also Figure 1 , natural seawater was used as the electrolyte, RuO2@ nickel foam electrodes were used as the two electrodes, and square waveform alternating current ( Figure 2 ) was used as a power source to electrolyze natural seawater, the voltages Ea (anode voltage) and Ec (cathode voltage) were 1.8 V and -1.8 V respectively, the period T was 0.5 s, and the electrolyte temperature was room temperature (25 °C).

[0072] During the electrolysis process, bubbles were observed to be continuously generated on both electrodes without precipitation, and the current was stable during the process.

[0073] Figure 6 The changes in hydrogen evolution during 80 minutes of continuous electrolysis were monitored, and the hydrogen evolution efficiency remained stable at around 12.80%.

[0074] Example 4

[0075] See also Figure 1 , using natural seawater as the electrolyte, titanium foam electrodes as the two electrodes, and square waveform alternating current ( Figure 2 ) was used as a power source to electrolyze natural seawater, the voltages Ea (anode voltage) and Ec (cathode voltage) were 4 V and -4 V respectively, the period T was 0.2 s, and the electrolyte temperature was room temperature (25 °C).

[0076] During the electrolysis process, bubbles were observed to be continuously generated on both electrodes without precipitation, and the current was stable during the process.

[0077] Figure 6 The changes in hydrogen evolution during continuous electrolysis for 60 minutes were monitored, and the hydrogen evolution efficiency remained stable at around 6.64%.

[0078] Example 5

[0079] See also Figure 1 , natural seawater was used as the electrolyte, RuO2@ nickel foam electrodes were used as the two electrodes, and square waveform alternating current ( Figure 2 ) was used as a power source to electrolyze natural seawater, the voltages Ea (anode voltage) and Ec (cathode voltage) were 1.8 V and -1.8 V respectively, the period T was 0.01 s, and the electrolyte temperature was room temperature (25 °C).

[0080] During the 100 min electrolysis, bubbles were observed to be continuously generated on both electrodes, and no precipitation was generated. The current remained stable during the electrolysis process.

[0081] The changes in hydrogen evolution during continuous electrolysis for 60 minutes were monitored, and the hydrogen evolution efficiency remained stable at around 1.05%.

[0082] Example 6

[0083] See also Figure 1 , natural seawater was used as the electrolyte, Pt electrodes were used as the two electrodes, and a sinusoidal alternating current ( Figure 7 ) as a power source for electrolysis of natural seawater, Figure 7 The Ea shown is 4 V, the period T is 1 s, and the electrolyte temperature is room temperature (25° C.) Within 5 h of electrolysis, it can be observed that both electrodes continue to generate bubbles during the electrolysis process, and no precipitation is generated, and the current remains stable during the electrolysis process.

[0084] Example 7

[0085] See also Figure 1 , natural seawater was used as the electrolyte, PtRh electrodes were used as the two electrodes, and triangular wave alternating current ( Figure 8 ) as a power source for electrolysis of natural seawater, Figure 8 The Ea shown is 3 V, the period T is 1 s, and the electrolyte temperature is room temperature (25° C.).

[0086] During the 10 h of electrolysis, bubbles were observed to be continuously generated on both electrodes without precipitation, and the current remained stable during the electrolysis process.

[0087] Comparative Example 1

[0088] Natural seawater was used as the electrolyte, RuO2@ nickel foam electrodes were used as the two electrodes, and direct current was used as the power source to electrolyze natural seawater. The constant voltage was 1.8V and the electrolyte temperature was room temperature (25°C). During the electrolysis process, bubbles were observed to be generated on the cathode. After 10 minutes of electrolysis, a certain amount of white precipitation was observed on the electrode surface. Fig. 9 , Fig. 9 The left picture is the picture before direct current electrolysis, and the right picture is the picture after direct current electrolysis). During the electrolysis process, the current density dropped significantly by 60% after 800s of electrolysis ( Fig.10 ).

[0089] Comparative Example 2

[0090] See also Figure 1 , natural seawater was used as the electrolyte, RuO2@ nickel foam electrodes were used as the two electrodes, and square wave alternating current ( Figure 1 ) as the power source, the voltage Ea (anode voltage) and Ec (cathode voltage) were 1.8V and -1.8V respectively, the cycle T was 4s, and the electrolyte temperature was room temperature (25°C). During the electrolysis process, bubbles were observed to be continuously generated on both electrodes, but the electrolysis process was accompanied by precipitation. At 20 minutes, obvious precipitation was observed to accumulate around the electrodes, which may be caused by the long cycle time.

[0091] The present invention Figure 1 A schematic diagram showing the principle of producing hydrogen by electrolyzing seawater with alternating current.

[0092] like Figure 1 As shown, the method for producing hydrogen by electrolysis of water of the present invention is illustrated by taking the electrolysis of seawater as an example. The method comprises: using natural seawater as an electrolyte, applying alternating current to electrodes, and utilizing the periodic change of the voltage of the alternating current to periodically switch the polarity of the electrodes between the cathode state and the anode state. When the electrodes are in the anode state, OH generated by the hydrogen evolution reaction in the cathode state is consumed. -To inhibit precipitation and decrease in electrode catalytic activity. Figure 1 In the embodiment, the electrolyte is seawater, and alternating current is applied between the left and right electrodes. In the first half cycle of alternating current, the white arrow near the left electrode indicates the hydrogen evolution reaction that occurs during the cathode state of the electrode, and at the same time, the right electrode is in the anode state and an oxygen evolution reaction or a chlorine-oxygen reaction occurs (as shown by the white arrow near the right electrode); in the second half cycle of alternating current, the black arrow near the left electrode indicates the oxygen evolution reaction or the chlorine-oxygen reaction that occurs during the anode state of the electrode, and at the same time, the right electrode is in the cathode state and a hydrogen evolution reaction occurs (as shown by the black arrow near the right electrode). Due to the periodic change of the alternating current voltage, the polarity of the electrode will be alternately switched between the cathode state and the anode state. In the present invention, with respect to the same electrode, the cathode state refers to the electrode as a cathode at this moment voltage to perform a hydrogen evolution reaction, and the anode state refers to the electrode as an anode at this moment voltage to perform an electrochemical oxidation reaction, including but not limited to oxygen evolution reaction and / or chlorine oxidation reaction.

[0093] Preferably, the cycle of the present invention is set to 0.01-2s. More preferably, the cycle of the present invention is set to 0.2-2s; and even more preferably, the cycle of the present invention is set to 0.25-2s.

[0094] Figure 2 A schematic diagram of square wave alternating current is shown.

[0095] Among them, Ea represents the voltage of the positive half cycle, Ec represents the voltage of the negative half cycle, and the period is T.

[0096] Figure 7 A schematic diagram showing a sinusoidal alternating current.

[0097] Wherein, Ea represents the peak voltage of the positive half cycle, Ec represents the peak voltage of the negative half cycle, and the period is T.

[0098] Figure 8 A schematic diagram of triangular wave alternating current is shown.

[0099] Wherein, Ea represents the peak voltage of the positive half cycle, Ec represents the peak voltage of the negative half cycle, and the period is T.

[0100] like Figure 2 , Figure 7 and Figure 8 As shown, the ordinate is voltage U and the abscissa is time t. The waveform of the alternating current is selected from any one of square wave, sine wave or triangle wave. Preferably, it is a square wave.

[0101] Figure 3 The effect diagram before and after the electrolysis of seawater using square wave alternating current in Example 1 is shown. Figure 3As shown, the electrolyte in the electrolytic cell remained clear at 40 minutes of electrolysis, and no insoluble precipitate was generated on the electrode surface. The clarity of the electrolyte was not significantly different from that before the start of electrolysis, i.e., at 0 minutes of electrolysis.

[0102] Figure 4 The current density-time curve of the electrolysis of seawater using square waveform alternating current in Example 1 is shown. Figure 4 In the current density-time curve shown, the ordinate is current density and the abscissa is time.

[0103] Figure 5 The gas chromatogram of gaseous products of seawater electrolysis by square wave alternating current in Example 1 is shown. Figure 5 As shown, the collected gas is pure hydrogen.

[0104] Figure 6 A graph showing the hydrogen evolution efficiency of electrolyzing seawater using square waveform alternating current of different periods in Examples 1-4.

[0105] Fig. 9 Figure 2 shows a comparison of the electrolytic cell before and after direct current electrolysis of seawater. Fig. 9 As shown, in Comparative Example 1, a certain amount of white precipitate was present on the electrode surface after 10 minutes of direct current electrolysis, and a large amount of white precipitate was observed at the bottom of the electrolytic cell.

[0106] Fig.10 Figure 2 shows a schematic diagram of the change in current density during direct current electrolysis of seawater. Fig.10 As shown, the ordinate is current density and the abscissa is time. In Comparative Example 1, the current density significantly decreased by 60% when the electrolysis lasted for 800s during the direct current electrolysis process, indicating that the precipitate had an adverse effect on the current density.

[0107] Fig.11 Example 19 shows that the Figure 1 The curve shown is the voltage of the sinusoidal alternating current on the two electrodes varying with time (one period T), and the data is recorded by an oscilloscope.

[0108] Fig.12 The graph shows the change of current density over time in Example 19. During the test time (60 min), the current density remained stable.

[0109] Fig.13 The curve of current density changing with time in one cycle in Example 19 is shown.

[0110] Fig.14 Example 23 shows that the Figure 1 The curve shown is the voltage of the triangular wave alternating current on the two electrodes changing with time (one period T), and the data is recorded by an oscilloscope.

[0111] Fig.15 The graph shows the change of current density over time in Example 23. During the test time (60 min), the current density remained stable.

[0112] Fig.16 The curve of current density changing with time in one cycle in Example 23 is shown.

[0113] It should be noted that the seawater selected for the examples of natural seawater in the present invention was taken from Qingdao City, Shandong Province, Weihai City, Shandong Province and Sanya City, Hainan Province, and the seawater from different regions had no significant effect on the experimental results.

[0114] Electrochemical signal generation and collection: A function generator (model Tektronix AFG3022C) and an electrochemical workstation (CHI660E, Shanghai Chenhua) were used to output alternating current and direct current. The electrochemical workstation was used to record electrochemical information such as current and voltage. An oscilloscope (model Tektronix TDS2022B) was used to record the voltage information actually applied to the two electrodes by the alternating current output by the function generator.

[0115] Gas product collection and analysis: The gas products produced by the electrolysis of seawater were collected by the drainage method, and the composition of the gas products produced by the electrolysis of seawater was tested and analyzed by gas chromatograph (Shimadzu GC2030).

[0116] Sediment analysis: The precipitation during the electrolysis process was observed with the naked eye, and a dynamic light scattering instrument (DynaPro NanoStar, Wyatt, USA) was used to further qualitatively analyze the precipitation in the solution after seawater electrolysis.

[0117] The present invention does not limit the electrolytic cell required for the embodiment, and it can be an electrolytic cell sold on the market. In the embodiment of the present invention, the electrolytic device used is a square electrolytic cell of 6cm×6cm×6cm as the electrolytic cell, and is equipped with corresponding electrodes to form an electrolytic device. According to the experimental results, it can be seen that the size of the electrolytic cell and the electrode has no effect on the experimental effects of the embodiments of the present invention.

[0118] The hydrogen evolution efficiency in the present invention refers to the Faraday efficiency of the hydrogen evolution reaction. The level of the hydrogen evolution efficiency directly affects the efficiency of converting electrical energy into hydrogen.

[0119] Faradaic efficiency refers to the percentage of actual products to theoretical products in an electrochemical reaction, reflecting the utilization efficiency of energy conversion.

[0120] In the electrode material provided by the present invention: RuO2@nickel foam electrode: the nickel foam is ultrasonically cleaned in acetone, anhydrous ethanol and 3mol / L HCl aqueous solution for 15 minutes, then repeatedly rinsed with deionized water and blown dry with a N2 gun for standby use. RuCl3 is dissolved in isopropanol under stirring to prepare a 2wt% RuCl3 isopropanol solution. The pretreated nickel foam (0.5cm×3cm) is placed in a porcelain boat (10mm×100mm×10mm), and a 2wt% RuCl3 isopropanol solution is dripped into the porcelain boat until the nickel foam is just immersed. Then, in an N2 atmosphere, the tubular furnace is heated to 60°C at a heating rate of 5°C / min, and the solution is evaporated by maintaining it at this temperature for 1h. Subsequently, the sample is placed in a muffle furnace, the muffle furnace is heated to 400°C at a heating rate of 5°C / min, the muffle furnace is kept at 400°C for 2h, and then the muffle furnace is naturally cooled to room temperature to obtain a RuO2@nickel foam electrode.

[0121] PtRh alloy electrode: PtRh alloy wire, diameter 0.27 mm, Rh content 11% (atomic ratio), purchased from Shanghai Boxiang Electrical Instrument Co., Ltd.

[0122] Nickel foam electrode, nickel sheet electrode, platinum electrode, graphite electrode, titanium electrode, titanium foam electrode, carbon paper electrode, and graphene electrode are common commercially available electrodes, and there are no special requirements for the shape and size of the electrodes.

[0123] In Examples 8-11 and Comparative Example 3, the experiments were conducted with periods T of 0.1s, 0.2s, 0.8s, 1.5s and 3s, and other conditions were the same as in Example 1.

[0124] Example 8

[0125] See also Figure 1 , natural seawater was used as the electrolyte, RuO2@ nickel foam electrodes were used as the two electrodes, and square waveform alternating current ( Figure 2 ) was used as a power source to electrolyze natural seawater, the voltages Ea (anode voltage) and Ec (cathode voltage) were 1.8 V and -1.8 V respectively, the period T was 0.1 s, and the electrolyte temperature was room temperature (25 °C).

[0126] After 60 minutes of electrolysis, it can be observed that bubbles are continuously generated on both electrodes, and no precipitation is generated. The current remains stable during the electrolysis process, and the hydrogen evolution efficiency is about 3.23%.

[0127] Example 9

[0128] See also Figure 1 , natural seawater was used as the electrolyte, RuO2@ nickel foam electrodes were used as the two electrodes, and square waveform alternating current ( Figure 2) was used as a power source to electrolyze natural seawater, the voltages Ea (anode voltage) and Ec (cathode voltage) were 1.8 V and -1.8 V respectively, the period T was 0.2 s, and the electrolyte temperature was room temperature (25 °C).

[0129] After 60 minutes of electrolysis, it can be observed that bubbles are continuously generated on both electrodes, and no precipitation is generated. The current remains stable during the electrolysis process, and the hydrogen evolution efficiency is about 5.57%.

[0130] Example 10

[0131] See also Figure 1 , natural seawater was used as the electrolyte, RuO2@ nickel foam electrodes were used as the two electrodes, and square waveform alternating current ( Figure 2 ) was used as a power source to electrolyze natural seawater, the voltages Ea (anode voltage) and Ec (cathode voltage) were 1.8 V and -1.8 V respectively, the period T was 0.8 s, and the electrolyte temperature was room temperature (25 °C).

[0132] After 60 minutes of electrolysis, it can be observed that bubbles are continuously generated on both electrodes, and no precipitation is generated. The current remains stable during the electrolysis process, and the hydrogen evolution efficiency is about 59.74%.

[0133] Embodiment 11

[0134] See also Figure 1 , natural seawater was used as the electrolyte, RuO2@ nickel foam electrodes were used as the two electrodes, and square waveform alternating current ( Figure 2 ) was used as a power source to electrolyze natural seawater, the voltages Ea (anode voltage) and Ec (cathode voltage) were 1.8 V and -1.8 V respectively, the period T was 1.5 s, and the electrolyte temperature was room temperature (25 °C).

[0135] After 60 minutes of electrolysis, it can be observed that bubbles are continuously generated on both electrodes, and no precipitation is generated. The current remains stable during the electrolysis process, and the hydrogen evolution efficiency is about 77.32%.

[0136] Comparative Example 3

[0137] See also Figure 1 , natural seawater was used as the electrolyte, RuO2@ nickel foam electrodes were used as the two electrodes, and square waveform alternating current ( Figure 2 ) was used as a power source to electrolyze natural seawater, the voltages Ea (anode voltage) and Ec (cathode voltage) were 1.8 V and -1.8 V respectively, the period T was 3 s, and the electrolyte temperature was room temperature (25 °C).

[0138] After 60 minutes of electrolysis, bubbles can be observed to be continuously generated on both electrodes, and white precipitate is produced as the reaction proceeds.

[0139] The gas produced by Examples 1-11 was collected by drainage method, and gas chromatography analysis showed that the gas produced by Examples 1-3, 5, 8-11 was pure hydrogen, and the gas produced by Examples 4, 6, and 7 was a mixture of hydrogen and oxygen.

[0140] Table 1: Comparison of the changes in hydrogen evolution efficiency and the effects of inhibiting precipitation in Examples 1-3, 5, 8-11 and Comparative Examples 2 and 3:

[0141] Table 1

[0142]

[0143]

[0144] Conclusion: When the AC cycle is within the range of 0.01-2s, direct seawater electrolysis for hydrogen production does not produce precipitation, and the hydrogen production efficiency increases with the increase of the cycle. When the cycle increases to 3s and 4s, precipitation occurs.

[0145] Example 12

[0146] See also Figure 1 , natural seawater was used as the electrolyte, RuO2@ nickel foam electrodes were used as the two electrodes, and square waveform alternating current ( Figure 2 ) was used as a power source to electrolyze natural seawater. The electrolyte temperature was room temperature (25°C), and the experiment was carried out by changing the voltage Ea (anode voltage), Ec (cathode voltage) and period T.

[0147] The gas produced by the electrolysis of each item 1-8 in Example 12 was collected by drainage method, and the gas product was analyzed by gas chromatography. The experimental results are shown in the following table:

[0148] Table 2

[0149]

[0150]

[0151] As can be seen from Table 2, when the voltage of the alternating current is 1.8-4V and the cycle is 0.01-2s, direct seawater electrolysis to produce hydrogen does not produce precipitation and the hydrogen evolution efficiency is greater than 1%.

[0152] Further, on the basis of Example 12, in order to verify that the cycle is 0.01-2s and the voltage is electrolyzed in the range of 1.8-4V, other conditions change and affect the technical effect, each time select one of the voltage and cycle ratios in 1-8 of Table 2 of Example 12, and each time only change one of the following experimental conditions for orthogonal experiments: electrolyte temperature (respectively 5°C, 20°C, 50°C, 70°C, 95°C), waveform (square wave, sine wave, triangle wave), electrode material (respectively using nickel foam, nickel sheet, Pt, PtRh alloy, carbon paper, graphite, titanium foam, titanium sheet, RuO2@nickel foam as two electrodes). Through multiple groups of orthogonal experiments, it can be seen that no matter how other conditions change, when the cycle of alternating current is 0.01-2s and the voltage is electrolyzed in the range of 1.8-4V, direct electrolysis of seawater to produce hydrogen can be achieved without precipitation, and the hydrogen evolution efficiency is greater than 1%. Technical effect. The gas products were analyzed by gas chromatography. The gas products produced when RuO2 / nickel foam electrode was used as the electrode were pure hydrogen, and the gas products produced when other materials were used as electrodes were a mixture of hydrogen and oxygen.

[0153] Embodiment 13

[0154] Only the electrode material was changed, and other conditions were the same as in Example 1, and the experiment was carried out (see Figure 1 , using natural seawater as the electrolyte and square wave alternating current ( Figure 2 ) was used as a power source to electrolyze natural seawater. The voltages Ea (anode voltage) and Ec (cathode voltage) were 3V and -3V respectively. The cycle T was 1s and the electrolyte temperature was room temperature (25°C). The generated gas was collected by the drainage method. The electrode materials used were nickel foam, nickel sheet, Pt, PtRh alloy, carbon paper, graphite, titanium foam, titanium sheet, and RuO2@nickel foam as two electrodes):

[0155] Table 3

[0156]

[0157]

[0158] In each experiment 1-9 in Table 3, after 40 min of electrolysis, it can be observed that bubbles are continuously generated on both electrodes and no precipitation is generated.

[0159] The gas produced by the electrolysis of the electrode materials 1-9 in Example 13 was collected by drainage method. Gas chromatography analysis showed that the direct electrolysis of seawater by alternating current to produce hydrogen could be achieved on different electrodes, and hydrogen was continuously produced without precipitation. The gas product produced when RuO2 / nickel foam electrode was used as the electrode was pure hydrogen, and the gas product produced when other materials were used as electrodes was a mixed gas of hydrogen and oxygen.

[0160] Embodiment 14

[0161] Other conditions were the same as in Example 1, except that the electrolyte temperature was changed and maintained by a constant temperature water bath, and the gas generated during the electrolysis was collected. (See Figure 1 , using natural seawater as the electrolyte and square wave alternating current ( Figure 2 ) was used as a power source to electrolyze natural seawater. The voltages Ea (anode voltage) and Ec (cathode voltage) were 1.8 V and -1.8 V, respectively, and the period T was 1 s. The generated gas was collected by the drainage method. The electrolyte temperatures were 5°C, 20°C, 50°C, 70°C, and 95°C).

[0162] Table 4

[0163]

[0164]

[0165] After 40 min of electrolysis, bubbles were continuously generated on both electrodes of each experiment in Table 4, and no precipitation was generated. The gas products were collected by drainage method, and the gas volumes at the end of the reaction are listed in Table 4.

[0166] The direct electrolysis of seawater with alternating current to produce hydrogen at different temperatures within the range of 5-95°C did not produce precipitation for 40 minutes of electrolysis; as the temperature increased, the volume of the collected gas increased, because the increase in temperature accelerated the electrochemical reaction rate, thus producing more gas per unit time. The collected gas products were all pure hydrogen when analyzed by gas chromatography.

[0167] Embodiment 15

[0168] Other conditions were the same as in Example 1, only the voltage was changed, and the gas was collected at the end of the reaction (see Figure 1 , natural seawater was used as the electrolyte, RuO2@ nickel foam electrodes were used as the two electrodes, and square waveform alternating current ( Figure 2 ) was used as the power source to electrolyze natural seawater. The voltages Ea (anode voltage) and Ec (cathode voltage) are shown in Table 5. The cycle T was 1 s and the electrolyte temperature was room temperature (25°C). The generated gas products were collected by the drainage method.

[0169] The effects of direct electrolysis of seawater by alternating current at different AC voltages are compared as follows:

[0170] Table 5

[0171] Serial number Voltage Ea, Ec (V) Gas volume collected (ml) Whether precipitation 1 ±1.8 17.3 no 2 ±2.5 26.7 no 3 ±3.5 39.8 no 4 ±4 45.5 no

[0172] After 40 min of electrolysis, bubbles were observed to be continuously generated on both electrodes, and no precipitation was generated. The gas volume at the end of the reaction is shown in Table 5.

[0173] Conclusion: When direct electrolysis of seawater with AC current was performed at different voltages within the range of 1.8-4V to produce hydrogen, no precipitation was produced during 40 minutes of electrolysis; as the voltage increased, the volume of the collected gas increased, because the increase in voltage accelerated the electrochemical reaction rate, thus producing more gas per unit time. The gas product was analyzed by gas chromatography and was pure hydrogen.

[0174] Example 16

[0175] The electrolysis was carried out using natural seawater as the electrolyte, with Example 1 as the benchmark, and the differences are shown in Table 6. (The natural seawater was used as the electrolyte, and the square waveform AC was used as the power source to electrolyze the natural seawater. The voltage Ea (anode voltage) and Ec (cathode voltage), AC cycle, electrolyte temperature, and electrode materials were all shown in Table 6. The generated gas was collected by the drainage method.

[0176] Among them, the electrode material is divided into RuO2@nickel foam electrode and other electrode materials. Other electrode materials are selected from any one of the following: nickel sheet electrode; or platinum electrode; or platinum-rhodium alloy electrode; or graphite electrode; or titanium electrode; or foam titanium electrode; or carbon paper electrode; or graphene electrode. The definitions of "other electrodes" in the following embodiments are all as described in this embodiment.

[0177] Table 6

[0178]

[0179]

[0180]

[0181]

[0182] On the basis of Table 6, further changing the waveform from square wave to sine wave or triangle wave can also achieve the technical effect of no precipitation and hydrogen evolution efficiency greater than 1%. At the same time, pure H2 is collected when RuO2@nickel foam electrode is used as electrode, and mixed gas of H2 and O2 is collected when other electrode materials are used as electrodes.

[0183] Furthermore, the present invention provides embodiments of sine waves and triangular waves at different periods, and the gas prepared in embodiments 17-24 is collected by drainage method.

[0184] Embodiment 17

[0185] See also Figure 1, using natural seawater as the electrolyte, RuO2@nickel foam as the two electrodes, and sinusoidal alternating current as the power source to electrolyze natural seawater. Ea (anode voltage) and Ec (cathode voltage) are 3V and -3V respectively, the cycle T is 0.2s, and the electrolyte temperature is room temperature (25℃). During the electrolysis process, it can be observed that both electrodes continue to generate bubbles during the electrolysis process, and no precipitation is generated, and the current remains stable during the electrolysis process.

[0186] The changes in hydrogen evolution during 60 minutes of continuous electrolysis were monitored, and the hydrogen evolution efficiency remained stable at around 6.17%.

[0187] Embodiment 18

[0188] See also Figure 1 , using natural seawater as the electrolyte, RuO2@nickel foam as the two electrodes, and sine wave alternating current as the power supply to electrolyze natural seawater. Ea (anode voltage) and Ec (cathode voltage) are 3V and -3V respectively, the cycle T is 0.5s, and the electrolyte temperature is room temperature (25℃). During the electrolysis process, it can be observed that both electrodes continue to generate bubbles during the electrolysis process, and no precipitation is generated, and the current remains stable during the electrolysis process.

[0189] The changes in hydrogen evolution during 60 minutes of continuous electrolysis were monitored, and the hydrogen evolution efficiency remained stable at around 13.03%.

[0190] Embodiment 19

[0191] See also Figure 1 , using natural seawater as the electrolyte, RuO2@nickel foam as the two electrodes, and sine wave alternating current as the power supply to electrolyze natural seawater. Ea (anode voltage) and Ec (cathode voltage) are 3V and -3V respectively, the cycle T is 1s, and the electrolyte temperature is room temperature (25℃). During the electrolysis process, it can be observed that both electrodes continue to generate bubbles during the electrolysis process, and no precipitation is generated, and the current remains stable during the electrolysis process.

[0192] The changes in hydrogen evolution during 60 minutes of continuous electrolysis were monitored, and the hydrogen evolution efficiency remained stable at around 18.60%.

[0193] Embodiment 20

[0194] See also Figure 1 , using natural seawater as the electrolyte, RuO2@nickel foam as the two electrodes, and sine wave alternating current as the power supply to electrolyze natural seawater. Ea (anode voltage) and Ec (cathode voltage) are 3V and -3V respectively, the cycle T is 2s, and the electrolyte temperature is room temperature (25℃). During the electrolysis process, it can be observed that both electrodes continue to generate bubbles during the electrolysis process, and no precipitation is generated, and the current remains stable during the electrolysis process.

[0195] The changes in hydrogen evolution during continuous electrolysis for 60 min were monitored, and the hydrogen evolution efficiency was stabilized at around 33.78%.

[0196] Embodiment 21

[0197] See also Figure 1 , using natural seawater as the electrolyte, RuO2@nickel foam as the two electrodes, and triangular wave alternating current as the power source to electrolyze natural seawater. Ea (anode voltage) and Ec (cathode voltage) are 3V and -3V respectively, the cycle T is 0.2s, and the electrolyte temperature is room temperature (25℃). During the electrolysis process, it can be observed that both electrodes continue to generate bubbles during the electrolysis process, and no precipitation is generated, and the current remains stable during the electrolysis process.

[0198] The changes in hydrogen evolution during continuous electrolysis for 60 minutes were monitored, and the hydrogen evolution efficiency remained stable at around 3.04%.

[0199] Embodiment 22

[0200] See also Figure 1 , using natural seawater as the electrolyte, RuO2@nickel foam as the two electrodes, and triangular wave alternating current as the power source to electrolyze natural seawater. Ea (anode voltage) and Ec (cathode voltage) are 3V and -3V respectively, the cycle T is 0.5s, and the electrolyte temperature is room temperature (25℃). During the electrolysis process, it can be observed that both electrodes continue to generate bubbles during the electrolysis process, and no precipitation is generated, and the current remains stable during the electrolysis process.

[0201] The changes in hydrogen evolution during continuous electrolysis for 60 minutes were monitored, and the hydrogen evolution efficiency remained stable at around 5.48%.

[0202] Embodiment 23

[0203] See also Figure 1 , using natural seawater as the electrolyte, RuO2@nickel foam as the two electrodes, and triangular wave alternating current as the power source to electrolyze natural seawater. Ea (anode voltage) and Ec (cathode voltage) are 3V and -3V respectively, the cycle T is 1s, and the electrolyte temperature is room temperature (25℃). During the electrolysis process, it can be observed that both electrodes continue to generate bubbles during the electrolysis process, and no precipitation is generated, and the current remains stable during the electrolysis process.

[0204] The changes in hydrogen evolution during continuous electrolysis for 60 minutes were monitored, and the hydrogen evolution efficiency remained stable at around 7.05%.

[0205] Embodiment 24

[0206] See also Figure 1, using natural seawater as the electrolyte, RuO2@nickel foam as the two electrodes, and triangular wave alternating current as the power supply to electrolyze natural seawater. Ea (anode voltage) and Ec (cathode voltage) are 3V and -3V respectively, the cycle T is 2s, and the electrolyte temperature is room temperature (25℃). During the electrolysis process, it can be observed that both electrodes continue to generate bubbles during the electrolysis process, and no precipitation is generated, and the current remains stable during the electrolysis process.

[0207] The changes in hydrogen evolution during continuous electrolysis for 60 min were monitored, and the hydrogen evolution efficiency was stabilized at around 20.42%.

[0208] The gas products prepared in Examples 17-24 were analyzed by gas chromatography and all were found to be pure hydrogen.

[0209] The present invention also provides a method for producing hydrogen by electrolysis of a solution that generates a precipitate under alkaline conditions, wherein a solution that generates a precipitate under alkaline conditions other than natural seawater is used as an electrolyte, an alternating current is applied to an electrode, and the polarity of the electrode is periodically switched between a cathode state and an anode state by utilizing the periodic change of the voltage of the alternating current. When the electrode is in the anode state, OH generated by the hydrogen evolution reaction in the cathode state is consumed. - To inhibit precipitation and the decrease of electrode catalytic activity; the other solution that generates precipitation under alkaline conditions includes a solution containing ions that can be precipitated under alkaline conditions.

[0210] By adopting the method of the present invention, river water, salt lake water, mine water, industrial waste water, domestic sewage, etc. can be directly used to prepare hydrogen, achieving the technical effects of abundant electrolyte sources, low cost, simple preparation method and high efficiency.

[0211] Preferably, the other solution that generates a precipitate under alkaline conditions is selected from a solution containing Ca 2+ Solutions and / or containing Mg 2+ of solution.

[0212] Preferably, the other solution that generates precipitation under alkaline conditions is selected from any one or more of the following: river water, salt lake water, mine water, industrial wastewater, and domestic sewage.

[0213] Preferably, the Ca 2+ and / or Mg 2+ The solution is selected from any one or more of the following: river water, salt lake water, mine water, industrial waste water, and domestic sewage.

[0214] Preferably, the cycle of the alternating current is 0.001-2s.

[0215] Preferably, the period of the alternating current is 0.001-0.01s.

[0216] Preferably, the cycle of the alternating current is 0.01-2s.

[0217] Preferably, the voltage of the alternating current is 1.2-380V.

[0218] Preferably, the voltage of the alternating current is 1.2-1.8V.

[0219] Preferably, the voltage of the alternating current is 1.8-4V.

[0220] Preferably, the voltage of the alternating current is 4-380V.

[0221] Preferably, the waveform of the alternating current is selected from a square wave, a sine wave or a triangle wave.

[0222] Preferably, the electrode is selected from one of RuO2@nickel foam electrode, nickel foam electrode, nickel sheet electrode, platinum electrode, platinum-rhodium alloy electrode, graphite electrode, titanium electrode, titanium foam electrode, carbon paper electrode and graphene electrode.

[0223] Furthermore, the type of electrolyte is changed to produce hydrogen, and the following embodiments are provided:

[0224] Embodiment 25

[0225] The seawater was replaced with salt lake water, and the salt lake water was used as the electrolyte. RuO2@nickel foam was used as the two electrodes, and square waveform alternating current was used as the power source to electrolyze the salt lake water. The voltage Ea (anode voltage) and Ec (cathode voltage) were 1.8V and -1.8V respectively, the cycle T was 1s, and the electrolyte temperature was room temperature (25°C). The generated gas was collected by the drainage method.

[0226] After 60 minutes of electrolysis, bubbles were observed to be continuously generated on both electrodes, and no precipitation was generated. The hydrogen evolution efficiency was greater than 1%. The gas product prepared in this embodiment was analyzed by gas chromatography, and it was pure hydrogen.

[0227] The present invention does not specifically limit the source of the salt lake water, and the salt lake water from any region on the earth can be used. The selected lake water will not affect the effect of the present invention.

[0228] Embodiment 26

[0229] The experimental methods of Example 26 are the same as those of Example 25, and the differences are shown in Table 7. (Brine water is used as the electrolyte, square wave AC is used as the power source to electrolyze the salt lake water, and the voltage Ea (anode voltage) and Ec (cathode voltage), AC cycle, electrolyte temperature, and electrode materials are all shown in Table 7).

[0230] Table 7

[0231]

[0232]

[0233]

[0234]

[0235] The experimental results of items 1 to 10 in Example 26 show that no precipitation is produced when the alternating current cycle is within the range of 0.01-2s; the hydrogen evolution efficiency is greater than 1%. When the gas product is analyzed by gas chromatography, when RuO2@ nickel foam electrode is selected as the electrode material, the gas product is pure hydrogen; when other electrode materials (nickel sheet electrode; or platinum electrode; or platinum-rhodium alloy electrode; or graphite electrode; or titanium electrode; or titanium foam electrode; or carbon paper electrode; or graphene electrode) are used as electrodes, the gas product is a mixture of hydrogen and oxygen.

[0236] On the basis of Examples 1-10 in Table 7, further changing the waveform from a square wave to a sine wave or a triangle wave can also achieve the technical effect of no precipitation; the hydrogen evolution efficiency is greater than 1%, and pure H2 is collected when the RuO2@nickel foam electrode is used as the electrode, and a mixed gas of H2 and O2 is collected when other electrode materials are used as electrodes.

[0237] Embodiment 27

[0238] See also Figure 1 , seawater was replaced with mine water, filtered mine water was used as electrolyte, RuO2@ nickel foam was used as two electrodes, and square waveform alternating current ( Figure 2 ) was used as the power source to electrolyze mine water, the voltage Ea (anode voltage) and Ec (cathode voltage) were 1.8 V and -1.8 V respectively, the cycle T was 1 s, and the electrolyte temperature was room temperature (25°C). The generated gas was collected by the drainage method.

[0239] After 60 minutes of electrolysis, bubbles were observed to be continuously generated on both electrodes, and no precipitation was generated. The hydrogen evolution efficiency was greater than 1%. The gas product was analyzed by gas chromatography and was pure hydrogen.

[0240] The purpose of filtering mine water is to filter out large particles such as sand, sand, algae, garbage and other impurities in the mine water to avoid adverse effects on electrolytic hydrogen production. The filtering method includes filtering the solution with ordinary filter paper.

[0241] The present invention does not specifically limit the source of the mine water, and the mine water can be from any region on the earth. The selected mine water will not affect the effect of the present invention.

[0242] Embodiment 28

[0243] The experimental methods of Example 28 are the same as those of Example 27, except for the differences shown in Table 8:

[0244] Table 8

[0245]

[0246]

[0247]

[0248]

[0249] The experimental results of items 1 to 10 in Example 28 show that no precipitation occurs when the alternating current cycle is within the range of 0.01-2s, and the hydrogen evolution efficiency is greater than 1%. It can also be seen that when RuO2@ nickel foam electrode is selected as the electrode material, pure hydrogen can be collected, and when other electrode materials (nickel sheet electrode; or platinum electrode; or platinum-rhodium alloy electrode; or graphite electrode; or titanium electrode; or titanium foam electrode; or carbon paper electrode; or graphene electrode) are used as electrodes, a mixed gas of hydrogen and oxygen is collected.

[0250] On the basis of Table 8, the waveform is further changed from square wave to sine wave or triangle wave for experiment. It can be seen from the experimental results that the same technical effect as that in Table 8 can be obtained. The technical effect of no precipitation and hydrogen evolution efficiency greater than 1% is achieved. At the same time, pure H2 is collected when RuO2@nickel foam electrode is used as electrode, and mixed gas of H2 and O2 is collected when other electrode materials are used as electrodes.

[0251] Embodiment 29

[0252] See also Figure 1 , the seawater was replaced by industrial wastewater, the filtered industrial wastewater was used as the electrolyte, RuO2@ nickel foam was used as the two electrodes, and a square waveform alternating current ( Figure 2 ) was used as the power source to electrolyze industrial wastewater, the voltage Ea (anode voltage) and Ec (cathode voltage) were 1.8 V and -1.8 V respectively, the cycle T was 1 s, and the electrolyte temperature was room temperature (25°C). The generated gas was collected by the drainage method.

[0253] After 60 minutes of electrolysis, bubbles were observed to be continuously generated on both electrodes, and no precipitation was generated. The hydrogen evolution efficiency was greater than 1%. The gas product was analyzed by gas chromatography and was pure hydrogen.

[0254] The present invention does not specifically limit the source of industrial wastewater, and the wastewater may be any industrial wastewater containing high concentrations of calcium ions, magnesium ions, and other metal ions that are easily precipitated under alkaline conditions. The effect of the present invention will not be affected by the different industrial wastewaters selected.

[0255] Embodiment 30

[0256] The experimental methods of Example 30 are the same as those of Example 29, except for the differences shown in Table 9:

[0257] Table 9

[0258]

[0259]

[0260]

[0261] The experimental results of items 1 to 10 in Example 30 show that no precipitation is generated when the alternating current cycle is within the range of 0.01-2s; the hydrogen evolution efficiency is greater than 1%. When the gas product is analyzed by gas chromatography, when RuO2@ nickel foam electrode is selected as the electrode material, the gas product is pure hydrogen; when other electrode materials (nickel sheet electrode; or platinum electrode; or platinum-rhodium alloy electrode; or graphite electrode; or titanium electrode; or titanium foam electrode; or carbon paper electrode; or graphene electrode) are used as electrodes, the gas product is a mixture of hydrogen and oxygen.

[0262] The purpose of filtering industrial wastewater is to filter out large particles of impurities in the industrial wastewater to improve efficiency.

[0263] On the basis of Table 9, the waveform is further changed from square wave to sine wave or triangle wave for experiment. From the experimental results, it can be seen that the technical effect of no precipitation and hydrogen evolution efficiency greater than 1% can also be achieved. At the same time, pure H2 is collected when RuO2@nickel foam electrode is used as electrode, and mixed gas of H2 and O2 is collected when other electrode materials are used as electrodes.

[0264] By adopting the method of the present invention, river water, domestic sewage, etc. are used as the electrolyte to prepare hydrogen, and the same technical effects as those of Examples 25-30 can also be achieved.

[0265] Embodiment 31

[0266] The electrolysis was carried out using natural seawater as the electrolyte, with Example 1 as the reference, and the differences are shown in the parentheses and Table 10. (The natural seawater was used as the electrolyte, and square wave AC was used as the power source to electrolyze the natural seawater, the voltage Ea (anode voltage) and Ec (cathode voltage) were 3V and -3V respectively, the electrode material was a platinum-rhodium alloy electrode, and the AC cycle and electrolyte temperature were as shown in Table 10). The generated gas was collected by the drainage method.

[0267] Table 10

[0268]

[0269]

[0270]

[0271] On the basis of the embodiments in Table 10, the waveform is further changed from a square wave to a sine wave or a triangle wave, or the electrolyte is changed to river water, salt lake water, mine water, industrial waste water, domestic sewage and other solutions that generate precipitates under alkaline conditions. The technical effect of collecting a mixed gas of H2 and O2 and not generating precipitation during the electrolysis process can also be achieved.

[0272] When RuO2@nickel foam electrode is used as an electrode, the technical effect of collecting H2 can be achieved. However, when other electrodes are used as electrodes, a mixed gas of H2 and O2 is collected.

[0273] In combination with other embodiments of the present invention, it can be known that when the alternating current cycle ranges from 0.001 to 2s, even if other conditions change, the technical effect of not generating precipitation and producing hydrogen can be achieved.

[0274] Embodiment 32

[0275] The electrolysis was carried out using natural seawater as the electrolyte, with Example 1 as the reference, and the differences are shown in the parentheses and Table 11. (Natural seawater was used as the electrolyte, square wave AC was used as the power source for electrolysis of natural seawater, the AC cycle was 1 s, the electrode material was a platinum-rhodium alloy electrode, the voltage Ea (anode voltage) and Ec (cathode voltage), and the electrolyte temperature were as shown in Table 11). The generated gas was collected by the drainage method.

[0276] Table 11

[0277]

[0278]

[0279]

[0280] On the basis of Table 11, the waveform can be further changed from a square wave to a sine wave or a triangle wave, or the electrolyte can be changed to river water, salt lake water, mine water, industrial waste water, domestic sewage and other solutions that generate precipitation under alkaline conditions. The technical effect of collecting a mixed gas of H2 and O2 and not generating precipitation during the electrolysis process can also be achieved.

[0281] When RuO2@nickel foam electrode is used as an electrode, the technical effect of collecting H2 can be achieved. However, when other electrodes are used as electrodes, a mixed gas of H2 and O2 is collected.

[0282] In combination with other embodiments of the present invention, it can be known that when the voltage range is 1.2-380V, even if other conditions change, the technical effect of not generating precipitation and producing hydrogen can be achieved.

[0283] Embodiment 33

[0284] The experimental methods of Example 33 are the same as those of Example 32, with the differences shown in parentheses and in Table 12. (Natural seawater is used as the electrolyte, square wave AC is used as the power source to electrolyze natural seawater, and the voltage Ea (anode voltage) and Ec (cathode voltage), AC cycle, electrolyte temperature, and electrode materials are all as shown in Table 12).

[0285] Table 12

[0286]

[0287]

[0288]

[0289]

[0290]

[0291]

[0292] It can be seen from Table 12 in combination with other embodiments of the present invention that when the voltage of the alternating current is 1.2-380V and the period is 0.001-2s, direct seawater electrolysis to produce hydrogen does not produce precipitation and hydrogen can be collected.

[0293] When RuO2@nickel foam electrode is used as an electrode, the technical effect of collecting H2 can be achieved. However, when other electrodes are used as electrodes, a mixed gas of H2 and O2 is collected.

[0294] On the basis of Table 12, the waveform can be further changed from a square wave to a sine wave or a triangle wave, or the electrolyte can be changed to river water, salt lake water, mine water, industrial waste water, domestic sewage and other solutions that generate precipitates under alkaline conditions. The technical effect of collecting H2 and not generating precipitation during the electrolysis process can also be achieved.

[0295] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A method for producing hydrogen by direct electrolysis of seawater with effective suppression of precipitation, characterized in that: Using natural seawater as the electrolyte, alternating current is applied to the electrodes. The polarity of the electrodes is periodically switched between the cathode state and the anode state by utilizing the periodic change of the alternating current voltage. When the electrodes are in the anode state, the OH generated by the hydrogen evolution reaction in the cathode state is consumed. - To inhibit precipitation and the decrease of electrode catalytic activity.

2. The method according to claim 1, characterized in that The waveform of the alternating current is selected from a square wave, a sine wave or a triangle wave.

3. The method according to claim 1, characterized in that The waveform of the alternating current is a square wave.

4. The method according to claim 1, characterized in that: The voltage of the alternating current is 1.8-4V.

5. The method according to claim 1, characterized in that: The cycle of the alternating current is 0.01-2s.

6. The method according to claim 1, characterized in that The electrode is selected from one of RuO2@nickel foam electrode, nickel foam electrode, nickel sheet electrode, platinum electrode, platinum-rhodium alloy electrode, graphite electrode, titanium electrode, titanium foam electrode, carbon paper electrode and graphene electrode.

7. The method according to claim 1, characterized in that The precipitate is Ca(OH)2 and Mg(OH)2.

8. The method according to claim 1, characterized in that The temperature of the electrolyte is 5-95°C.

9. The method according to claim 1, characterized in that: The electrolyte is derived from natural seawater from any region on Earth.

10. The method according to claim 1, characterized in that The specific working mode of the method is: When the electrode is in the cathode state, a hydrogen evolution reaction occurs near the electrode, producing hydrogen and OH. - When the electrode is converted to the anode state, oxygen evolution reaction and / or chlorine oxidation reaction occur near the electrode, consuming the OH generated in the cathode state. - .

11. The method according to claim 1, characterized in that The voltage of the alternating current is 1.2-380V.

12. The method according to claim 1, characterized in that The cycle of the alternating current is 0.001-2s.

13. A method for producing hydrogen by electrolysis of a solution in which a precipitate is generated under alkaline conditions, characterized in that: A solution other than natural seawater that generates precipitation under alkaline conditions is used as the electrolyte. Alternating current is applied to the electrodes. The polarity of the electrodes is periodically switched between the cathode state and the anode state by utilizing the periodic change of the alternating current voltage. When the electrode is in the anode state, the OH generated by the hydrogen evolution reaction in the cathode state is consumed. - To inhibit precipitation and decrease in electrode catalytic activity; The other solutions that generate precipitates under alkaline conditions include solutions containing ions that can be precipitated under alkaline conditions.

14. The method according to claim 13, characterized in that The other solution that generates precipitation under alkaline conditions is selected from any one or more of the following: river water, salt lake water, mine water, industrial wastewater, domestic sewage; preferably, the other solution that generates precipitation under alkaline conditions is selected from Ca 2+ Solutions and / or containing Mg 2+ of solution.

15. The method according to claim 13, characterized in that The cycle of the alternating current is 0.01-2s.

16. The method according to claim 13, characterized in that The voltage of the alternating current is 1.8-4V.

17. The method according to claim 13, characterized in that The cycle of the alternating current is 0.001-2s.

18. The method according to claim 13, characterized in that The voltage of the alternating current is 1.2-380V.

19. The method according to claim 13, characterized in that The waveform of the alternating current is selected from a square wave, a sine wave or a triangle wave.

20. The method according to claim 13, characterized in that The electrode is selected from one of RuO2@nickel foam electrode, nickel foam electrode, nickel sheet electrode, platinum electrode, platinum-rhodium alloy electrode, graphite electrode, titanium electrode, titanium foam electrode, carbon paper electrode and graphene electrode.

21. The method according to any one of claims 13 to 20, characterized in that: The temperature of the electrolyte is 5-95°C.

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