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Scientific Reports Volume 5, Article Number: 16263 (2015) Cite this article

The use of light or electricity to split water for hydrogen production is the most developed "green technology". In order to improve the efficiency of hydrogen production, currently, the most exciting and booming strategy is focused on efficient and inexpensive catalysts. Here, we report an innovative idea of ​​a highly efficient hydrogen evolution reaction (HER) that uses plasma to activate liquid water through thermal electron transfer to reduce the hydrogen bond structure. This strategy is effective for all HER in acidic, alkaline and neutral systems, photocatalytic systems with g-C3N4 (graphite carbon nitride) electrodes, and inert systems with ITO (indium tin oxide) electrodes. Compared with deionized water, the efficiency of HER is increased by 48% based on the ex-situ activated water on the Pt electrode. When the in-situ current on the nano-particle Au electrode is -20 mA, the energy efficiency of activated water is increased by 18%. In addition, the starting potential of -0.023 V relative to RHE is very close to the thermodynamic potential of HER (0 V). The current density measured at the corresponding overpotential of HER in the acidic system is higher than any data previously reported in the literature. This method opens up new prospects for clean and green energy production.

Due to increasingly serious environmental pollution, renewable fuels such as hydrogen are being regarded as clean energy sources. The use of light or electricity to split water for hydrogen production is the most developed "green technology". In order to improve the efficiency of hydrogen production, currently, the most exciting and vigorously developing strategies focus on efficient and inexpensive catalysts 1, 2, 3, 4, 5, and 6. The electrochemical decomposition of water can be carried out using visible light with appropriate energy, while photochemical decomposition generally uses semiconductor-based materials7,8. Importantly, the success of these technologies for hydrogen production energy conversion depends on the development of highly efficient and earth-rich catalysts3,9. Other methods have also been developed, such as the construction of a monolithic photovoltaic photoelectrochemical device 10 and an attempt to use an electronically coupled proton buffer 11 to decouple the evolution of hydrogen and oxygen. Water has a tetrahedral structure with two OH bonds, which enables it to form a flexible dynamic hydrogen bond network. Raman spectroscopy has been successfully used for detection12,13,14,15. Increasing the electrolysis temperature can reduce the electrolysis voltage16 and the fact that water has a more disordered structure and weaker hydrogen bonds12 at the evaluation temperature inspired us to use the prepared small water clusters (SWC) for effective hydrogen evolution at room temperature. Based on this strategy, Au nanoparticles (NPs) with well-defined local surface plasmon resonance (LSPR) are often used in research focused on surface-enhanced Raman scattering (SERS)17 and in clinical settings for tumor photothermal ablation 18. In our previous report, they were used to achieve the hot electron transfer required to break the water-hydrogen bond. The weak/reduced interaction energy in water molecules provides potential applications for the development of efficient catalyst-free hydrogen production by reducing the onset potential. In this work, pure water prepared with SWC was innovatively used for efficient hydrogen evolution reaction (HER). The effect of in-situ preparation of SWC on the correspondingly improved HER efficiency was also demonstrated.

Figure 1a shows that Au NPs loaded in water have an obvious surface plasmon absorption band centered at 538 nm and a wider absorption band in the entire visible light region. The LSPR of Au NPs shows that under full-wavelength visible light irradiation (to generate RHBW based on fluorescent lamps), hot electron transfer can be achieved to destroy the hydrogen bond of a large amount of water, and the wavelength can be further enhanced by using optimized light (to produce highly reduced hydrogen Bond water, HRHBW, based on green light-emitting diodes). Unless otherwise stated, blank water was prepared under deionized (DI) lighting using indoor fluorescent lamps. In the preparation of blank water, Au NPs are not present. Under the illumination of a green light-emitting diode (LED, λmax 530 nm), the process of water treatment with Au NPs is shown in Figure 1b.

The process of preparing highly reduced hydrogen-bonded water (HRHBW) under the resonance illumination of Au NPs.

HRHBW is characterized by Raman spectroscopy. (a) Absorption spectra of supported Au NPs. (b) Under the resonance illumination of LED (λmax 530 nm), the schematic setup of preparing plasma activated liquid water based on the LSPR effect of Au NPs. (c) OH stretched Raman spectra of various waters. (d) Use fluorescent lamps and green LEDs to irradiate the prepared treated water DNHBW over time.

Figure 1c shows the OH tensile Raman spectra observed with various pure water samples. Use the preparation conditions similar to the preparation of RHBW to obtain a blank, but without light. According to the methods in documents 15, 17, and 18, these Raman spectra are further deconvolved into five Gaussian subbands. All samples are deconvolved with five Gaussian components with center wave numbers of 3018, 3223, 3393, 3506, and 3624 cm-1. In addition, the full width at half maximum (FWHM) of each component in the five Gaussian fitting is the same for all samples. For the 3018, 3223, 3393, 3506, and 3624 cm-1 bands, the respective values ​​are 234, 201, 176, 154, and 112 cm-1, respectively. The frequency bands on the low-frequency and high-frequency sides are related to the strong and weak hydrogen bonding OH characteristics, respectively. In this work, the three components on the low-frequency side are allocated to hydrogen-bonded water, and the remaining two high-frequency side components are allocated to non-hydrogen-bonded water. The non-hydrogen bonding water (DNHBW) is defined as the ratio of the area of ​​the non-hydrogen bonding OH stretch band to the total stretch band area. As shown in Table S1, the DNHBW values ​​of deionized water, RHBW, blank water and HRHBW are respectively 21.43±0.05% (deionized water stored for 4 weeks is 21.48%), 24.32±0.08%, 21.52±0.17% and ±26.33 0.11% (n = 3). The small difference between fresh and stored deionized water values ​​indicates that 21.43% is a reliable reference value for bulk water used in DNHBW. The similar values ​​of 21.43% and 21.52% of DI and blank water indicate that HRHBW cannot be obtained without the LSPR effect of light irradiating Au NP. Encouragingly, by taking advantage of the LSPR effect of supported Au NPs, DNHBW increased significantly from 21.43% to 24.32%. DNHBW increased by 13%, which can be increased to 23% by green LED lighting, which shows that this light is more effective in reducing the hydrogen bond structure. This effect was also observed in the static preparation of treated water based on fluorescent lamps and green LEDs (Figure 1d and supporting information, SI). In addition, the water treatment confirmed the effect of LSPR on the corresponding RHBW, with different DNHBW (Table S1 and SI). The range of DNHBW values ​​listed in Table S1 is 21% ~ 30%. The energy efficiency η when preparing HRHBW is estimated based on the ratio of the energy required to break the hydrogen bonds in bulk water to the energy provided by the LED light energy, and is defined as follows:

The hydrogen bond energy EHB of 20 kJ mol-1 is used. In order to obtain 75 g (or 75 cm3, using a density of 1 g cm−3) of HRHBW, calculate the number of moles of bulk water in which the hydrogen bond breaks Mwater in deionized water (21.46 %) and HRHBW (26.23%) of DNHBW. The power of the LED used, PLED, is 16 W, and the lighting time t of 75 cm3 deionized water through the glass tube is about 10 watts. 1500 seconds. Therefore, if ignoring the energy loss of LED scattering and light penetrating the glass tube, the energy efficiency of preparing HRHBW is about 4.0 kJ/24 kJ = 17%.

Deionized water, ceramic particle treated (CPT) water, and gold-plated CPT water samples were prepared at a temperature of 50 °C, and compared with deionized water, blank water, and RHBW prepared at room temperature. The measured OH tensile Raman spectra of these samples (prepared at 50°C) after cooling in laboratory ambient air at room temperature are shown in Figure S1. For deionized water, CPT water, and gold-plated CPT water, the corresponding values ​​of DNHBW are 21.37%, 21.36%, and 21.35%, respectively. Comparing the DNHBW values ​​of deionized water, CPT water and HRHBW (prepared at room temperature) are 21.46%, 21.24%, and 26.23%, respectively, indicating that the amount of joule used for heating contributes little to the successful preparation of HRHBW.

As recently shown20, the electrochemical properties of phenol and quinone in organic solvents are strongly affected by hydrogen bonds. As shown in Figure 2a, the first (Epred(1)) and second (Epred(2)) reduction peaks of benzoquinone (BQ) move to a lower negative potential, and when deionized water, one of them The potential difference between (ΔEp) drops and joins CH3CN to form hydrogen bond species. These phenomena are more significant for treated water, especially HRHBW prepared under LED lighting. For example, for H2O (0.69 M), using RHBW and HRHBW (see Table S2 for reduction peak shift), the reduction in ΔEp was enhanced by 6.3% and 11%, respectively (compared to deionized water). This indicates that there is more "free water" in the treated water, and the hydrogen bond is weaker, and it can interact strongly with BQ through the hydrogen bond. Further evidence of more "free water" by mixing with ethanol. Dissolve 10 wt% deionized water and HRHBW in two ethanol samples. The water content of deionized water and HRHBW measured by the volumetric Karl Fischer titration method (Metrohm 870 KF Titrino plus) were 10.87 and 10.34 wt%, respectively 21. Since HRHBW with weaker hydrogen bonds can form more hydrogen bonds with ethanol, compared with deionized water, the measured effective water content is reduced by 4.8%. In addition, use the Randles-Sevcik equation to calculate the diffusion coefficient of K3Fe(CN)6 in water from cyclic voltammetry data to check the new characteristics of HRHBW22:

The chemical behavior of BQ and K3Fe(CN)6 in different water.

(a) The volt-ampere data record of BQ in CH3CN, where CH3CN contains 0.2 M n-Bu4NPF6 as supporting electrolyte and 0.69 M H2O of different water at room temperature. (b) Voltammetric data recorded in various solutions with 50 mM K3Fe(CN)6 and 3 mm diameter flat Pt electrodes.

Where A is the area of ​​the electrode (the Pt electrode used is 0.07 cm2), n is the number of electrons involved in the reaction, equal to 1, and C is the concentration of probe molecules in the solution. When using RHBW instead of traditional deionized water, the calculated diffusion coefficient increased from 6.5 × 10-6 to 8.4 × 10-6 cm s-1, an increase of 29% (Figure 2b). In addition, when HRHBW (12 × 10−6 cm s−1) is used, the diffusion coefficient is increased by 85%. In addition, the reduced ΔV (potential difference between a pair of anode and cathode peaks) observed in the treated water indicates that the redox reaction of K3Fe(CN)6 in the treated water is more easily reversible.

In addition, in the presence of Ch, compared with steam generated from DI water, the chemical activity of steam generated by HRHBW was examined at room temperature to reduce Au-containing complexes to Au NPs. The results show that the steam generated from HRHBW acts as a weak reducing agent (Figure S2, S3, SI). This discovery opened up a new green way for chemical reduction.

Weak hydrogen-bonded water encourages us to evaluate its effective hydrogen evolution reaction, because the electrolysis of HRHBW requires less energy. As shown in Figure 3a about the CV in the second scan, the two pairs of nearly reversible peaks related to hydrogen desorption-adsorption of <0.1 V are not clearly defined in deionized water, but are clearly defined in RHBW23, 24. is DI Similar CV data recorded with blank water shows once again that lack of lighting does not change the characteristics of the water (Figure S4, S5, SI). After the 10th scan, in the experiment using deionized water and RHBW, both pairs of peaks were clearly defined; however, the area related to hydrogen desorption-adsorption in RHBW is much larger. After the 20th scan, the ΔV of hydrogen desorption-adsorption (1 and 1') observed in RHBW decreased from 0.019 to 0.009 V, and during the underpotential deposition period (2 and 2'), the hydrogen desorption-adsorption was ΔV decreased from 0.024 to 0.005 V, which indicates that the hydrogen desorption-adsorption reaction in RHBW is more easily reversible23,24. The apex of the anode shows that the corresponding oxygen evolution onset potential in RHBW is relatively low, especially in the second scan.

Voltammetric data of hydrogen evolution in various types of water with H2SO4 as the supporting electrolyte and planar Pt electrodes.

(a) Cyclic voltammograms of the second, 10th, and 20th scans in 0.5 M H2SO4 at a scan rate of 0.5 V s-1; the illustration shows the comparison of deionized water and blank (no light) The 10th scan of the experiment performed for comparison. (b) Linear sweep voltammogram (LSV) of different concentrations of H2SO4 at a scan rate of 0.05 V s-1; the inset shows the hydrogen evolution current of -0.4 V and Ag/AgCl in various waters with different concentrations of H2SO4. (c) Preparation 0, 1, 3, 5 and 7 days (in 0.5 M H2SO4, the scan rate is 0.05 V s-1). The hydrogen evolution reaction is carried out on the inert catalytic electrode (ITO) and the photocatalytic (g-C3N4/ITO) electrode. (d) Deionized water containing 0.5 M H2SO4 based on ITO electrode and LSV of hydrogen evolution in HRHBW. (e) The efficiency of HER based on HRHBW is improved, and the applied potential is shown in Figure 3d. (f) Based on g-C3N4/ITO electrode, with and without white LED lighting, LSV for hydrogen evolution reaction in deionized water containing 0.5 M Na2SO4 and HRHBW.

As shown in Figure 3b, regarding the linear sweep voltammogram (LSV) of deionized water, RHBW and HRHBW, the onset potential of the cathode HER is more positive in RHBW, especially in HRHBW, indicating that HER needs Energy can be reduced by weakening the hydrogen bond. Record and compare the HER current at -0.4 V (see the inset in Figure 3b) to avoid the interference of the generated hydrogen bubbles. As expected, the absolute value of the current increases as the electrolyte concentration increases. It is encouraging that HER has been significantly improved in the treated water. Compared with deionized water, the hydrogen evolution efficiency is increased by about 17% and 48%, respectively. Using RHBW and HRHBW [in 0.5 M H2SO4 at -0.4 V (Table S3)]. In addition, the efficiency of metastable water treatment depends on the storage time (Figure 3c). In addition, for the DI water and HRHBW systems, the calculated Faraday hydrogen production efficiency is 84.0 ± 5.4% and 86.2 ± 3.5%, respectively (see SI).

Pt electrode is considered to be an excellent catalyst for the electrolysis of water. The above results show that compared with deionized water based on Pt electrode system, HRHBW has a highly efficient hydrogen evolution reaction. In order to eliminate the influence of Pt during the electrolysis process, indium tin oxide (ITO) electrodes are used instead of Pt electrodes. As shown in Figure 3d, compared with the Pt electrode, the current at -0.6 V is much smaller, indicating that the ITO electrode is not conducive to the electrolysis of water. In addition, the efficiency of HER at –0.2, –0.3, –0.4, –0.5, and –0.6 V potentials increased by 204%, 374%, 424%, 200%, and 36.2%, respectively (Figure 3e). The continuous improvement in cathodic scanning efficiency from –0.2 to –0.4 V is attributed to the lower initial potential required for HER using HRHBW instead of DI water. At a lower cathode potential, the difference in HER efficiency is mainly determined by the difference in the interaction of water molecules. However, as the cathode potential further increases from –0.4 V to –0.6 V, this advantage decreases. This indicates that as the applied cathode overpotential increases, along with overcoming the difference in water molecular interactions between HRHBW and DI water, a more effective water split is sufficiently high. In contrast, the discussion about overpotential is based on the same reference electrode in this work. These results show that even with inert ITO electrodes, high-efficiency HER can be performed in HRHBW-based systems.

In addition, the well-known g-C3N4 HER catalyst was deposited on the ITO electrode to evaluate the effect of using HRHBW on the improvement of HER efficiency in 0.5 M Na2SO4. In recent years, g-C3N4 has attracted widespread attention due to its catalytic activity in visible light photocatalytic decomposition of water25,26. It is a visible light active polymer semiconductor with a band gap of about 2.7 eV and a corresponding light wavelength of about 460 nm27. This suitable belt structure makes it useful for effective water reduction and oxidation. As shown in Figure 3f, the current density recorded on the g-C3N4/ITO electrode in the HRHBW system is higher than that in the deionized water system from 0 to –0.6 V in the cathodic scan. Under no light conditions, the current density is -3.79 μA cm-2 at -0.6 V HRHBW system. Compared with the deionized water system (-3.38 μA cm-2), the HER efficiency has increased by 12.1%. In addition, under the irradiation of white light LED, the current density obtained by deionized water and HRHBW under no light conditions increased by 5.6% and 3.4%, respectively. Compared with the deionized water system, the lower current density increase obtained in the HRHBW system can be attributed to the lower charge transfer effect from the g-C3N4 photocatalyst to water under light. In the preparation of HRHBW, this similar charge transfer occurs in treated deionized water from hot electron transfer. Therefore, the charge transfer from g-C3N4 to HRHBW contributes less to HER in electrolysis water decomposition. Under the illumination of the white LED, the current density of the HRHBW system at -0.6 V is -3.92 μA cm-2. Compared with the deionized water system (-3.57 μA cm-2), the efficiency of HER is increased by 9.8%. In summary, these results indicate that the use of HRHBW to improve HER can be used for all types of electrodes, including active (Pt), photocatalytic (g-C3N4) and inert (ITO) electrodes. Further inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that the concentration of slightly dissolved Au metal in the RHBW is about approx. 0.62 ppb (HRHBW is approximately 0.65 ppb). The dissolved Au ions may be deposited on the Pt electrode, which may help increase the current in the HER. The influence of slightly dissolved Au ions in the RHBW on the corresponding effective HER is excluded, as shown in Figure S7 (similar to the experiment carried out in Figure 3). After performing the first HER on the polished platinum electrode based on deionized water, in subsequent experiments based on deionized water, HRHBW, deionized water and HRHBW, the used Pt electrode was only rinsed with deionized water without further Polished. The first and third experiments based on deionized water are similar to HER. The second and fourth experiments based on HRHBW are similar to HER. Therefore, the influence of slightly dissolved gold ions on the effective HER in HRHBW is excluded.

In addition, the influence of HRHBW with weak hydrogen bonds on the corresponding hydrogen evolution reactions in neutral and alkaline systems was further evaluated. As shown in Figure 4a, in the HRHBW-based system, the overpotential (10 mA cm-2) at pH -0.3 is 0.24 V, which is a decrease of 0.03 V compared to the DI water-based system. In addition, in the HRHBW-based system, the overpotential at 1 mA cm-2 is 0.21 V, which is a decrease of 0.01 V compared to the DI water-based system. In addition, it has a small Tafel slope (43.0 mV decimal -1) (Figure 4d).

Hydrogen evolution reaction on an inert catalytic electrode (ITO) in electrolytes with different pH values.

Record the LSV curve on the Pt electrode in (a) 1 M H2SO4 (pH -0.3), (b) 0.2 M KCl (pH 7) and (c) 2 M KOH (pH 14.3). (d) The corresponding Tafel chart is at pH 0.3, 7.0 and 14.3. Black line: electrolyte solution based on deionized water. Pink line: electrolyte solution based on HRHBW water.

Similarly, a decrease in the overpotential and a decrease in the Tafel slope of the HRHBW-based system were also observed at pH 7.0 and 14.3 (Figure 4b-d, Table S4). It is worth noting that, unlike acidic electrolytes, achieving efficient hydrogen evolution reactions in neutral and alkaline systems is considered a daunting challenge. For example, HER in acidic media is about 2 to 3 orders of magnitude higher than HER in alkaline media. Nevertheless, compared to the DI water-based system, the HRHBW-based system reduces the Tafel slope by nearly 5% at all pH values. This clearly shows that the interaction within water molecules is one of the main factors to improve efficiency and will be applicable to all pH systems. In addition, as discussed in SI, the hydrogen bonds in water molecules can be broken directly on the electrochemically rough Au substrate under fluorescent irradiation.

Therefore, the in-situ reduction of the water-hydrogen bond binding to HER was evaluated on the Au electrode deposited with Au NP under light. The SEM image showed that a large amount of Au NP was deposited on the Au electrode by the electrochemical oxidation-reduction cycle (ORC) method (Figure 5a). In addition, a mechanism for improving HER through simultaneous formation and electrolysis of HRHBW was proposed (Figure 5b). It can be observed that when the rough Au electrode is irradiated with a fluorescent lamp, the onset potential of the cathode HER is corrected, especially under the irradiation of a green LED (Figure 5c). As expected, HER was significantly promoted when Au electrodes were illuminated with fluorescent lamps (compared to non-light conditions) or green LEDs. Compared with non-light conditions, the hydrogen evolution efficiency is significantly improved by approx. 31% and 59% are based on experiments conducted under lamp and LED lighting, respectively (Table S5, SI). When deionized water is further replaced by HRHBW, based on the use of green LEDs to form HRHBW in situ, this increase increases to 84% (Figure S6). In addition, at specific current yields of -20, -30, and -40 mA, the energy efficiency of HRHBW is increased by 18%, 16%, and 14%, respectively, compared to bulk water (see SI).

The linear scanning voltammogram of the electrochemically rough Au electrode hydrogen evolution in deionized water containing 0.5 M H2SO4 under different light sources.

(a) SEM image of rough Au electrode (0.283 cm2) prepared using electrochemical oxidation-reduction cycle (ORC). (b) The draft reveals a combination of in-situ production and splitting (H)RHBW. (c) LSV of hydrogen evolution on electrochemically rough Au electrodes with different illumination sources (lamp and green LED) in deionized water containing 0.5 M H2SO4.

In recent literature reports on improving the efficiency of HER in water splitting, the focus of research is to reduce the cost of HER. In water electrolysis, two strategies are usually used to improve efficiency: reducing the cathode overpotential and increasing the specific surface area of ​​the electrode. Although Pt-based electrodes are widely considered to be useful as catalysts in water electrolysis, the high cost of this precious metal is worrying. Therefore, scientists are trying to develop cheaper but novel materials to make efficient electrodes 28, 29, 30, 31, 32, 33. However, on the other hand, the research on the internal water molecule interaction that affects the efficiency of electrolysis is usually neglected. Our experimental results show that the onset potential (defined as cathode current) rises rapidly as more negative potentials are applied, and it is -0.268 (-0.046) on Pt cathodes using DI water, RHBW and HRHBW-based electrolytes,- 0.253 (-0.031) and -0.245 (-0.023) V vs AgCl (vs RHE). These onset potentials of RHBW and HRHBW-based electrolytes are very close to the thermodynamic potential of HER (ie 0 V and RHE). As far as we know, the current density of the HER of the HRHBW-based electrolyte under the corresponding overpotential is higher than any current density reported in the literature for the Pt or Au catalyst system in the acid electrolyte (Table 1) 31, 32, 33, 34, 35 , 36. However, it should be remembered that unlike the reported Pt modified electrode with high surface area in DI water-based electrolyte, even with the smooth Pt electrode used in this work, the HRHBW-based electrolyte exhibits the highest HER efficiency.

Experimental results show that water molecules with reduced hydrogen bonding can easily be electrolyzed. These results are consistent with the facts revealed by density functional theory (DFT), where the interaction energy of H3O -OH− is 46.9 kJ mol-1; this energy increases ca. When H3O binds to the other four water molecules through hydrogen bonds, it is 2.5 times 37. In this work, we proposed a basic but important relationship between the interaction of water molecules and the efficiency of HER on Pt and Au electrodes. Obviously, it is feasible to reduce the onset and overpotential of HER by reducing the hydrogen bonds of water molecules. This innovative method may be applicable to currently developed catalysts to further improve its HER efficiency.

In short, we innovatively use the LSPR of Au NPs to prepare water with reduced hydrogen bonds. Reduced hydrogen-bonded water has many new properties, including high-efficiency HER in water splitting. This opens up new prospects for clean and green energy production. We believe that these new methods based on prepared RHBW will lead to various applications in the fields of medicine, biology and chemistry.

Sodium chloride, tetra-n-butylammonium hexafluorophosphate (n-Bu4NPF6, 98%), sulfuric acid and hydroquinone were purchased from Sigma-Aldrich Organics. Acetonitrile was purchased from Tedia. All reagents are used as is, no further purification is required. 40-mesh sieving ceramic particles for filtering deionization (DI) (molar composition: 92% SiO2, 3.0% Na2O and K2O, 2.0% Fe2O3, 1.5% Al2O3, 0.5% CaO, 0.5% MgO and other rare metal oxide ) Water was purchased from Chyuan-Bang Enterprise, Taiwan. Commercial chitosan (Ch) powder with a degree of deacetylation of 0.82 was purchased from Taiwan's No. 1 Chemical Factory. All solutions were prepared using deionized water (18.2 MΩ cm) provided by the Milli-Q system. All experiments were performed in an air-conditioned room for approximately 1 hour. 24°C. The water temperature is approx. 23.5°C.

The Au NPs in the aqueous solution are obtained from Au flakes (purity 0.9999) using electrochemical and thermal reduction methods. Generally, the gold electrode is circulated 200 times in a deoxygenated aqueous solution (40 mL) containing 0.1 N NaCl and 1 g L-1 chitosan (Ch) from -0.28 to 1.22 V vs Ag/AgCl at 500 mV s-1 Scan and stir gently. The duration of the apex of the cathode and anode is 10 and 5 seconds, respectively. Immediately, without changing the electrolyte, heat the solution in air from room temperature to boiling at a heating rate of 6 °C min-1. After cooling, the clear Au NP-containing solution is separated from the precipitated Ch. The solution containing Au NP was then placed in an ultrasonic bath for 30 minutes and centrifuged at 3600 rpm for a further 2 minutes to remove any Ch to prepare pure Au NP in the solution.

Immerse the washed ceramic particles in a solution containing 30 ppm AuNP for 1 day. Then thoroughly rinse the ceramic particles adsorbing AuNPs with deionized water, and finally dry them in an oven at 100°C for 1 day. Subsequently, the prepared AuNPs adsorbed ceramic particles were put into a glass tube (ID: 30 mm, L: 300 mm) equipped with a valve. Before the water is treated, the AuNPs adsorbed ceramic particles in the glass tube are rinsed with deionized water for several cycles until the pH value is constant (about pH 7.23 and water temperature about 23.5 °C).

Ultraviolet-visible absorption measurement of Au NPs supported by ceramic particles was carried out by using Perkin-Elmer Lambda 800/900 spectrophotometer. In order to measure the spectra of Au NPs loaded with solid ceramic particles based on the reflection model, the spectrophotometer is equipped with an integrating sphere collector. The wetted ceramic particles were used as a background reference in the experiment.

Deionized water (pH 7.23, T = 23.5 °C) is passed through a glass tube containing AuNPs to adsorb ceramic particles under light. The water treated under fluorescent light is called RHBW, and the water treated under green light-emitting diodes (LED) is called HRHBW. Then, collect the treated water (pH 7.25, T = 23.3 °C) in a glass sample bottle for subsequent testing as soon as possible. In order to check the purity of the prepared RHBW, further inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that the concentration of slightly dissolved metals in RHBW was approximately Au 0.62 ppb, Na 43 ppb, K 25 ppb, Al 23 ppb, Mg 13 ppb , Ca 4.5 ppb, Fe 0.41 ppb. Excluding gold, the total equivalent molar concentration of these dissolved metals is equal to approx. 6.9 × 10-6 N. The measured value of dissolved metals in deionized water is approx. 2.4 × 10−7 N is used as a reference. In addition, the total equivalent molar concentrations of slightly dissolved gold and other dissolved metals in the blank water are 0.57 ppb and 5.2 × 10-6 N, respectively.

Seal the prepared water in a 0.5 mL cell with a glass window. A confocal microscope was used to obtain Raman spectra (mini-Raman spectrometer, UniRAM-Raman type). The microscope used a diode laser operating at 532 nm and the output power on the sample was 1 mW. Use a 50x, 0.36 NA Olympus objective lens (working distance of 10 mm) to focus the laser on the sample. The laser spot size is approximately. 2.5 microns. A 1024 × 128 pixel thermoelectric cooling Andor iDus charge-coupled device (CCD) operating at -40°C is used as a detector with 1-cm-1 resolution. All spectra are calibrated relative to a 520 cm-1 silicon wafer. In the measurement, a 180° geometry is used to collect scattered radiation. A 325 notch filter is used to filter the excitation line from the collected light. The acquisition time for each measurement is 1 second. Thirty consecutive measurements were collected for each sample.

Add two samples of deionized water (20 mL) to a sealed glass sample cell (50-mL), place them together on the platform of the orbital shaker and run at 150 rpm. The bottom of each cell contains Au NP (approximately 20 ml) supported by ceramic particles, which is used to treat water under fluorescent light (RHBW) or green LED (HRHBW) lighting. The treated water samples are collected at specific times and their corresponding Raman spectra are measured. The value of non-hydrogen bond water (DNHBW) is calculated according to the aforementioned method and definition, and displayed in the text.

First, the gold-containing complex (approximately 250 ppm) was electrochemically prepared in deionized water using a method similar to that described in the previous report. Generally, when preparing a composite containing Au, the Au electrode is scanned 500 times at 500 mV s-1 from -0.28 V (holding for 10 seconds) to 1.22 V (holding for 5 seconds) in a deoxygenated aqueous solution containing 1 M NaCl . Subsequently, 2 g of L-1 Ch was added to the Au complex-containing solution and gently stirred for 10 minutes to prepare a stock solution as the precursor of Au NPs. Then 10 mL of stock solution was dropped on qualitative filter paper (pore size 11 μm, diameter 90 mm, lot number 10809161, Toyo Roshi Kaisha, Japan). Immediately place the wetted paper on the openings of two glass sample cells (50 mL), each sample cell containing deionized water and 40 mL of high RHBW (HRHBW), placed in the laboratory ambient air for 3 days. Use high-resolution X-ray photoelectron spectroscopy (HRXPS) to check the oxidation state of Au NPs and Au salts (precursors of Au NPs). In the measurement, a ULVAC PHI Quantera SXM spectrometer with monochromatic Al Kα radiation, 15 kV and 25 W, and 0.1 eV energy resolution was used. In order to compensate for the surface charging effect, all HRXPS spectra refer to the C 1 s neutral carbon peak at 284.8 eV.

The electrochemical behavior of K3Fe(CN)6 was evaluated in a three-electrode system consisting of a Pt electrode (0.07 cm2), a Pt sheet, and Ag/AgCl as the working electrode, counter electrode, and reference electrode, respectively. The measured value is obtained in water containing 50 mM K3Fe(CN)6 at a scan rate of 0.1 V s-1.

The hydrogen evolution reaction (HER) is measured by linear sweep voltammetry (LSV) in a three-electrode system, which consists of polished Pt electrodes (0.07 cm2) or ITO electrodes (0.28 cm2), Pt chips and Ag/AgCl, respectively It is the counter electrode and the reference electrode. The corresponding electrochemical measurement was performed in a 50 mL solution containing 0.5 M H2SO4 at a scan rate of 0.05 V s-1. Prior to HER, the aqueous solution had been carefully deoxygenated by bubbling highly purified nitrogen for 30 minutes.

The graphite carbonitride (g-C3N4) catalyst was synthesized by heat-treating urea (30 g) in an alumina crucible with a lid in a muffle furnace at 550°C for 3 hours. The resulting powder was rinsed with deionized water and ethanol to remove any remaining alkaline substances, and then collected by filtration before drying. Mix 10 μL of g-C3N4 (0.5 g mL-1) with 10 μL of dimethyl sulfoxide. The mixture was then dropped on indium tin oxide (ITO) glass (1 cm2), and then heated at 200 °C for 1 hour to improve the adhesion of the catalyst on the ITO electrode.

How to cite this article: Hwang, B.-J. etc. An innovative strategy for hydrogen evolution reaction using active liquid water. science. Rep. 5, 16263; doi: 10.1038/srep16263 (2015).

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The author thanks the Ministry of Science and Technology of the Republic of China and Taipei Medical University for financial support.

Hwang Bing-Joe and Chen Hsiao-Chien made the same contribution to this work.

Department of Chemical Engineering, National Taiwan University of Science and Technology, No. 43, Section 2, Keelung Rd., 10607, Taipei, Taiwan

Bing-Joe Hwang & John Rick

Department of Biochemistry and Molecular Cell Biology, School of Medicine, Taipei Medical University, 250 Wuxing Street, Taipei 11031, Taiwan

Hsiao-Chien Chen, Fu-Der Mai, Hui-Yen Tsai & Yu-Chuan Liu

Biomedical Imaging Research Center, Taipei Medical University, 250 Wuxing Street, Taipei 11031, Taiwan

Mai Fude and Liu Yuchuan

Graduate School of School of Medicine, Taipei Medical University, 250 Wuxing Street, Taipei 11031, Taiwan

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YCL conceived the idea of ​​the project and wrote the manuscript. BJH and HCC designed experiments. HCC, HYT and CPY conducted experiments. BJH, HCC and FDM analyzed the experimental data. YCL, BJH, HCC, FDM and JR discussed the results and commented on the paper.

The author declares that there are no competing economic interests.

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Hwang, BJ., Chen, HC., Mai, FD. etc. An innovative strategy for hydrogen evolution reaction using active liquid water. Scientific Report 5, 16263 (2015). https://doi.org/10.1038/srep16263

DOI: https://doi.org/10.1038/srep16263

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