Oxygen-Evolution on in-Situ Selective Formation ... - ACS Publications

Subscriber access provided by Lancaster University Library

C: Surfaces, Interfaces, Porous Materials, and Catalysis

Oxygen-Evolution on in-Situ Selective Formation AgO: Plane is the Key Factor Dandan Li, Congcong Wei, Qiang Wang, Lin Liu, Dazhong Zhong, Genyan Hao, Zhijun Zuo, and Qiang Zhao J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b00880 • Publication Date (Web): 11 Apr 2019 Downloaded from http://pubs.acs.org on April 11, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Oxygen-Evolution on in-Situ Selective Formation AgO: Plane is the Key Factor Dandan Li,ab Congcong Wei,ab Qiang Wang,ab Lin Liu,ab Dazhong Zhong,ab Genyan Hao,ab Zhijun Zuoab, Qiang Zhao* ab a Research

Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan

030024, Shanxi, P.R. China. b Shanxi

Key Laboratory of Gas Energy Efficient and Clean Utilization, Taiyuan

030024, Shanxi, P.R. China.

ABSTRACT: In this work, a method of synthesizing AgO exposed with different planes by electrodeposition using an unbuffered solution and a complexing agent as an electrolyte was first proposed. The experimental results indicate that the oxygen-evolution activity of AgO crystal exhibits very obvious facet-dependent properties. AgO crystals with mainly {111} exposed faces yield a superior catalytic activity over those with mainly {202} exposed faces under electrochemical water oxidation conditions, which agrees with the theoretical calculations. The AgO film with dominant {111} facets has a modest overpotential of 418 mV and its catalytic performance is demonstrated by long-term electrolysis at 2.03 V versus a reversible hydrogen electrode in a near-neutral potassium phosphate solution. A stable current density of 3.7 mA cm−2 persist for at least 6 h, and a Faradaic efficiency of 93% is

ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 25

obtained, which is much better than other Ag-based electrodes, especially current densities.

1. INTRODUCTION Splitting water to produce hydrogen and oxygen is a convenient method for energy conversion1-2. The oxygen-evolution reaction (OER) 2H2O→4H++O2 +4e− (in acid) or 4OH−→2H2O+O2+4e− (in base) represents a significant efficiency loss in water-splitting systems with slow kinetics3-4. Research on water-oxidation catalysts has focused on many transition metals, including Co-based catalysts catalysts

8-9,

Cu-based catalysts

10-12

and Fe-based catalysts

13-15.

5-7,

Ni-based

Our research group

has studied novel silver oxygen-evolution catalysts16, followed by a series of studies 17-19.

However, the reported Ag-based oxygen-evolution catalysts (OECs) possess

limited crystal structures and planes, even though the deliberate fabrication of other metallic OECs with special faces

20

has been rarely reported. The morphology and

exposed planes influence the electrocatalytic efficiency significantly

21-25.

We have

devoted significant attention to surface engineering to obtain an increased eletrocatalytic activity of the planes. The controlled synthesis of Ag-based OEC with special exposed facets is the most promising route to improve the catalytic activity and structural stability. Herein, we demonstrate a facile and efficient process for the synthesis of AgO exposed with different planes by potentionstatic deposition in unbuffered potassium nitrate electrolyte solution with different volumes of ammonia that can be complexed


Page 3 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


with silver at room temperature. The good compatibility between ammonia and electrolyte is beneficial to the anodic deposition of Ag+. It is because ammonia can increase the pH of solution and change the patterns of Ag+, and it can also serve as a proton carrier during the deposition process. The electrocatalytic performance studies indicate that these AgO crystals exhibit very obvious facet-dependent properties. The prepared AgO crystals with mainly {111} exposed faces show higher electrocatalytic activities than AgO crystals with mainly {202} exposed faces. Theoretical calculations show that the reaction activity of the AgO {111} surface is larger than that of the AgO {202} surface, which contributes to an enhanced catalytic activity. 2. EXPERIMENTAL SECTION 2.1 Materials and Chemicals Tripotassium phosphate trihydrate (K3PO4·3H2O, 99.0%), silver nitrate (AgNO3, 99.8%), potassium nitrate (KNO3, 99.0%) and iridium oxide (IrO2, 99.9%) were from Aladdin Chemistry Co. Ltd. (Shanghai, China). Ammonia (NH3·H2O, 25%) was from Tianjin Chemical Industrial Co. Ltd. (Tianjin, China). All chemicals were used without further purification. Ultrapure water with a resistivity of 18 MΩ cm−1 or higher was used to prepare all solution. Indium tin oxide-coated (ITO) glass slides (≤ 10 Ω sq−1 surface resistivity) were purchased from Kaivo Optoelectronic Technology Co. Ltd. (Zhuhai, China). 2.2 Preparation of Ag-based catalysts electrode Ag-based catalysts exposed with special planes were prepared by using potentiostatic method. First, 0.33 mmol NH3·H2O was added to 100 mL of 0.1 M



KNO3 solution under stirring to obtain a uniform solution. Second, this solution was transferred to an H-electrochemical cell with glass frit film. In particular, the anode chamber additionally contained 1 mM Ag+, while the cathode did not. Then electrochemically deposited was carried out until the charge reaches 1.5 C and the deposition voltage was 1.105 V vs. Ag/AgCl 26. During potentiostatic deposition, the working electrode was the ITO-coated glass with1 cm  5 cm, which was cleaned in acetone, ethanol and ultrapure water for 5 minutes in turns prior to use. Generally, the area of ITO immersed in the solution is 1 cm2. The auxiliary electrode was a platinum pole (1 mm diameter, 10 mm height) and the reference electrode was a Ag/AgCl (saturated KCl) electrode. After reaction, the ITO electrode was taken out, rinsed with ultrapure water, dried in the air, and then stored for the subsequent experiments. Other Ag-based catalysts were prepared by adjusting the amount of ammonia to 0.495 mmol, 0.660 mmol, and 0.825 mmol, respectively, while other conditions are consistent. 2.3 Characterization All catalysts were characterized by Powder X-ray diffraction (XRD) using a Rigaku Miniflex II diffractometer (Japan) with Cu–Kα radiation at 30 kV and 15 mA. Scanning electron microscopy (SEM) characterizations were carried out with a Hitachi SU8010 scanning electron microscope (Hitachi, Japan). All SEM images were obtained at an acceleration voltage of 3 kV. X-ray photoelectron spectroscopy (XPS) was performed on a WSCAL-ab 220i-XL spectrometer (VG Scientific, Sussex, UK)


Page 4 of 25

Page 5 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


with Al–Kα radiation. High-resolution transmission electron microscopy (HRTEM) images were obtained by using a JEM2010 microscope (Japan) equipped with a fieldemission gun at 200 kV. 2.4 Electrochemical test ITO electrode with catalyst was used as working electrode. Platinum pole and Ag/AgCl (saturated KCl) electrode were used as the counter and reference electrodes, respectively. Cyclic voltammetry (CV) curves were collected at 50 mV s−1 scan rates in the potentials from 0–1.4V vs. Ag/AgCl in 0.1 M K3PO4 solution. Steady-state currents were tested using linear sweep voltammetry (LSV) with a scan rate of 1 mV s-1 and a potential range of 0 to 1.5 V vs. Ag/AgCl. Stability test for oxygen evolution was carried out at an applied potential of 1.105 V vs. Ag/AgCl in 0.1 M K3PO4 solution. Before the data was collected, the solution resistance with a value of 60 Ω was first measured in fresh electrolyte with a clean ITO electrode using potentiostatic EIS, which was used to correct the iR drop of the Tafel plot. The overpotential was obtained with compensated at 1mA cm-2. A Faraday efficiency experiment was carried out in a H-compartment electrochemical cell with 40 mL of 0.1 M K3PO4 electrolyte in the anode and cathode electrode compartments, which was custom-built and well sealed. The oxygen concentration was measured with a GC-2014 gas chromatograph with a thermal-conductivity detector and helium carrier gas, under the chromatographic conditions of oven temperature 60 ° C, detector temperature 150 ° C, and carrier gas flow rate 30 mL min-1. All the measured potentials vs. the Ag/AgCl were converted to RHE by the equation (ERHE = EAg/AgCl + 0.197 + 0.059 × pH).



2.5 Preparation of IrO2 electrode Generally IrO2 was chosen as the benchmark electrocatalyst for the OER. Assuming that all of the charge is used to deposit the silver-based catalysts without any other consumption, up to 1.9 g cm-2 of AgO can be generated. Firstly, 6 mg of catalyst was added to a solution containing 300 μL of ethanol and 15 μL of 5 wt% Nafion solution .The suspension solution was ultrasonicated for 30 min in order to obtain a uniform ink solution. Then 100 µL of the ink solution was droped on the ITO (1 × 1 cm2) with a loading of approximately 1.9 mg cm-2. Finally, the electrode was dried in air. 2.6 Calculation Calculations were performed using the Vienna Ab-initio Simulation Package (VASP)

27-29.

Calculations were conducted with the generalized gradient

approximation with the PBE exchange–correlation functional 30. A plane-wave energy cutoff of 415 eV was used for all geometry optimizations. The K point was sampled by using a 3 × 3 × 1 Monkhorst–Pack mesh. The transition state (TS) was derived by using the nudged-elastic-band method 31. The equilibrium lattice constants of AgO were a = 5.758, b = 3.476 and c = 5.585 Å, which was consistent with the experimental value of a = 5.86, b = 3.48 and c = 5.50 Å, aAu = 4.078 and aMoC = 4.278 Å32. AgO (111) (1 × 2) (40 AgO units in a cell) and AgO (202) (2 × 2) (48 AgO units in a cell) surfaces were modeled using a fifteen- and six-layered slab, in which the vacuum region was 15 Å. During the calculations, the bottom three layers of the AgO (111) surface and the two layers of the AgO (202)


Page 6 of 25

Page 7 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


surface were fixed at bulk positions, whereas the other layers with the adsorbates were allowed to relax, and the volume was maintained constant. Other calculation details see the supplement. 3. RESULTS AND DISCUSSION After potentionstatic deposition, a layer of grey black material covered the surface of ITO, which showed that Ag-based catalysts were produced in 0.1 M potassium nitrate with different ammonia concentrations, which contain 1 mM Ag+ at 1.105 V (vs. Ag/AgCl). Figure 1 shows the scanning electron microscopy (SEM) images and XRD patterns of the as-prepared Ag-based catalysts, which were prepared by altering the concentration of ammonia, and maintaining the molar ratio of AgNO3 to KNO3 at 1:100. The SEM image of as-prepared Ag-based catalysts with 3.30 mM NH3·H2O indicates that truncated cubes formed on the ITO surfaces (Figure 1a). As the NH3·H2O concentration increased from 3.30 mM to 4.95 mM, 6.60 mM and 8.25 mM, the truncated cubes structures are etched increasingly. The Ag-based particles prepared with 8.25 mM NH3 H2O were found to be triangular prisms, as shown in Figure 1d, with an average size of 200 nm. The diffraction peaks can be indexed well to AgO (JCPDS PDF-# 43-1038) except for the five peaks at 21.27°, 30.15°, 35.17°, 50.77° and 60.40°, which are characteristic of ITO. The (202) peak is remarkably strong in intensity for the truncated cubes prepared with 3.30 mM ammonia, which confirms that the truncated cubes are bound mainly by the {202} facets. With



Figure 1. SEM images and XRD patterns of Ag-based catalysts obtained at 1.105 V (vs. Ag/AgCl) from different concentrations of NH3·H2O on the ITO electrode: (a) 3.30 mM, (b) 4.95 mM, (c) 6.6 mM, (d) 8.25 mM.

ammonia addition, the intensity of the (111) peak increases relative to that of the (2 02) peak in the triangular prisms. For the AgO prepared with 8.25mM ammonia, the (


Page 8 of 25

Page 9 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


111) becomes strong compared with the (202) peak because of the substantial presence of {111} faces. Figure 2a-2b shows SEM images and corresponding schematic drawings of the AgO monoclinic crystal synthesized with 3.30 mM and 8.25 mM ammonia. Different crystal facets of a truncated cube and a triangular prism are also labeled. SEM images show the AgO crystals viewed along the [202] direction of a truncated cube and the [ 111] direction of a triangular prism. The reason for the formation of AgO with different morphologies may be that the crystal growth rate in different crystal directions will change slightly as the concentration of ammonia in solution increases. At lower ammonia concentrations, the growth rate along the [202] directions may be slower than that along the [111] directions. At a higher ammonia concentration, the growth rates along the [111] directions are reduced, which lead to the formation of a triangular prism. Detailed structural information of the synthesized AgO crystals synthesized with (a) 3.3 mM and (b) 8.25 mM ammonia was investigated by HRTEM. Figures 2c and 2d show a large number of two kinds of lattice fringes with interplane distances of 0.23 and 0.28 nm, which can be attributed to the (202) and (111) facets, respectively. Based on the above analysis, the surfaces of the two AgO particles are enclosed by many independent (202) and (111) facets. XPS studies show that the AgO produced with 8.25 mM ammonia was divalent. The Ag 3d spectrum exhibits two contributions, 3d5/2 and 3d3/2 (that result from the



Figure 2. SEM images, corresponding schematic drawings and HRTEM images of AgO crystals synthesized with (a,c) 3.3 mM, (b,d) 8.25 mM ammonia.

spin–orbit splitting), located at 368.2 and 374.2 eV, respectively (Figure 3a) and that were in the range for Ag (II) bound to O. O1s peaks (Figure 3b) at a binding energy of 528.8, 530.9 and 533 eV that correspond to the O-Ag(II), chemisorbed surface OH on Ag and adsorbed molecule water, respectively 33-36. The ability to synthesize AgO crystals with mainly {202} and {111} exposed faces enables the investigation of their surface properties. The oxygen-evolution activity of four AgO anodes was measured in 0.1 M K3PO4. Figure 4a shows the cyclic voltammetrys (CVs) curves of AgO electrodes covered on ITO in 0.1 M K3PO4. Compared with the noble-metal IrO2/ITO catalysts, the four AgO samples showed excellent OER activity during CVs scans from 0.92–2.32 V (vs. RHE). For convenience, we defined the four AgO catalysts prepared with 3.30 mM, 4.95 mM,


Page 10 of 25

Page 11 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. X-ray photoelectron spectra of AgO crystals synthesized with 8.25 mM on ITO substrates.

6.60 mM and 8.25 mM ammonia as AgO-OEC1, AgO-OEC2, AgO-OEC3 and AgO-OEC4, respectively. The black plot was the control experiment in a clean K3PO4 solution with bare ITO as the working electrode, and which demonstrated no appreciable OER activity under the same conditions. The plots of AgO-OECs showed appreciable catalytic waves, which indicated that the existence of AgO were essential for the catalytic reaction. Under an identical potential (2.03 V vs. RHE) for OER based on the CVs data, the catalytic current density of AgO-OEgC4 was the highest in the four AgO samples. Bulk electrolysis experiments for oxygen evolution were performed in the same electrolyte. The chronoamperometry curves are the average currents obtained by testing three times to reduce the test deviation (Figure 4b), and these results are consistent with their CVs data.

As shown in Figure S8, the average current density

curves with the error bars show a maximum deviation of 13%, indicating good repeatability of the catalysts. At an applied potential of 2.03 V (vs. RHE), the AgO-OEgC4 electrode was stably catalyzed for 6 hours at a current density of ~ 3.7



mA cm-2 (kelly line). Furthermore, there is a slight current enhancement in the initial of electrolysis, which may be due to the cracking of catalyst that yielded a larger surface area (Figure S9). Catalyst AgO-OEC1 showed a low catalytic stability and catalytic activity (blue line) during water oxidation. The different catalytic properties toward OER may result from their dissimilar particle size and exposed crystal plane. In order to determine the crystal plane is the main factor affecting its performance, the influence of catalyst size should be excluded first. The AgO with mainly exposed {-111} crystal planes, which particle size was similar to that of the mainly exposed {-202} crystal planes made in the potassium nitrate, was prepared in a solution of potassium acetate and ammonia as an electrolyte, but its catalytic performance was obviously superior

26

(see Figures S10−S12 for additional XRD, SEM images and

current-density plots of samples discussed in this work). In addition, after 6h of stability testing, the XRD spectra of AgO were performed to determine their electrochemical stability. Figure S13 shows that there is no significant change except for the decrease in the intensity of the diffraction peak, indicating the better electrochemical stability of AgO. The conclusion that these AgO crystals exhibited obvious facet-dependent properties was underpinned by experimental findings. The electrochemical performance of AgO film was further studied, as shown in Figure 4c, the Tafel plots of AgO-OEC4 derived from the OER polarization curves was obtained in 0.1 M potassium phosphate. It shows that the Tafel slope of AgO-OEC4 is 77 mV dec-1. Extrapolation from the linear equation, y = 0.077x + 0.649, shows that the overpotential at a current density of 1 mA cm−2 is 418 mV,


Page 12 of 25

Page 13 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


which is less than most of the reported in-situ formation of transition metal catalysts (Table S1). These results strongly demonstrate that the AgO crystals with mainly {1 11} exposed faces is a highly efficient OER catalyst, especially for high current densities. Subsequently, the oxygen concentration in the sealed space was measured by gas chromatography to determine the amount of oxygen in the product under constant potential electrolysis in 0.1 M potassium phosphate (pH 12.3) (Figure 4d). But first ensure that the oxygen in the confined space has been removed before the start of the experiment. Since the dissolved oxygen consumes some oxygen, the oxygen release rate is slightly lower during the initial stage of oxygen evolution. After 4 hours of the

Figure 4. (a) CVs and (b) current-density plots obtained by using AgO-OECs as the working electrode for the water-oxidation reaction in 0.1 M KPi solution at pH 12.3. (c) Tafel plot, η = (Vappl – iR – EpH), for the AgO-OEC4 in a 0.1 M KPi buffer at pH 12.3, where η is the overpotential, iR indicates the uncompensated solution resistance and EpH is the thermodynamic potential for water splitting at the corresponding pH. The Tafel slope of the AgO-OEC4 is 77 mV dec−1. (d) Change in O2 concentration showing oxygen production for AgO-OEC4 at 2.03 V vs. RHE.



experiment, the Faradaic efficiency was 93%. According to the above results, it is found that the increase of ammonia concentration is benefit to the exposed planes of the AgO(111) surface, and then the surface is favor of OER. In order to explain the two results, the surface energy of AgO(hkl) surface and the reaction of OER on AgO(hkl) surface are studied by using DFT. XRD result shows that AgO (111) and AgO (202) surfaces are mainly exposed planes, so only both surfaces are considered. For clean AgO (111) and AgO (202) surfaces, the surface energies are 475 and 764 J/m2 (Figure 5a-5b), which indicates that the AgO (111) surface area is larger than that of the AgO (202) surface. Originally, the electrolyte pH is lower and the surface is covered mainly by H2O. The first H2O adsorbs on AgO (111) and AgO (202) surfaces which is dissociative adsorption, and the surface energies are lower than that of the corresponding clean surface. The stability of both surfaces increases because of the H2O adsorption. With an increase in adsorption numbers of H2O, both surface energies increase. Therefore, the AgO (111) and AgO (202) surfaces are covered by one H2O at 298 K in KNO3 with added ammonia solution, and the corresponding surface energies are 169 and 116 J/m2. The result indicates that the AgO (202) surface area is larger than that of the AgO (111) surface at lower electrolyte pH, which is accordance with our XRD result. OH adsorption on AgO (111) and AgO (202) surfaces is similar to H2O adsorption. When one OH adsorbs on AgO (111) and AgO (202) surfaces, the surface energies are least at 298 K, and the corresponding surface energies are 86 and 97 J/m2,


Page 14 of 25

Page 15 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


respectively. The surface area of the AgO (202) surface is smaller than that of the AgO (111) surface. In addition, the surface energies for OH adsorption on the AgO (1 11) and AgO (202) surfaces (86 and 97 J/m2) are smaller than for H2O adsorption on both surfaces (169 and 116J/m2). Thus, the probability of OH adsorption increases with an increase in ammonia. As a result, the AgO (111) surface area is larger than that of the AgO (202) surface with increasing pH. These results agree with our XRD results. The co-adsorption behavior of OH and H2O on the AgO (111) and AgO (202) surfaces is also calculated. The surface energies of one OH and one H2O that co-adsorb on the AgO (111) and AgO (202) surfaces are 263 and 190 J/m2, respectively, which are larger than that the corresponding single OH or H2O adsorption on both surfaces. Therefore, the probability of OH and H2O co-adsorption is small. Bronsted, Evans and Polanyi was combined with linear scaling relations to estimate the activation energy by reaction-energy changes of the elementary reaction on the corresponding catalytic processes without calculating the corresponding transition states

37.

That is, a more endothermic reaction yields a higher corresponding

activation energy, which is used in previous studies

38-41.

DFT studies show that one

water or OH adsorbs AgO (111) and AgO (202) surfaces are the most stable adsorption structure, so OER is only considered on one H2O or OH precovered surface. Differences in reaction energies for the same pathways on OH or H2O precovered AgO (111) and AgO (202) surfaces are only ~0.1–0.19 eV, which indicates that OH or H2O adsorption is not key to the reaction activity, as shown in



一

Figure 5. Surface energy for different numbers of H2O or OH adsorption on AgO ( 1 11) (a) and AgO (202) (b) surfaces at 298 K (Blue and red lines represent H2O and OH adsorption). Reaction energy of OER on one H2O (c) and OH (d) precovered AgO (111) and AgO (202) surfaces at pH 12.8 and 298 K (Black and red lines represent AgO (111) and AgO (202) surfaces).

Figure 5c-5d. The activation energy of 3OH− + OH* + e− → 2OH− + O* + H2O (l) +2e− on OH or H2O precovered AgO (111) and AgO (202) surfaces are largest among


Page 16 of 25

Page 17 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the four pathways, which is the highest energy consumption step. The reaction energies of 3OH− + OH* + e- → 2OH− + O* + H2O (l) + 2e− on the H2O and OH precovered AgO (111) surfaces are smaller than on the H2O and OH precovered AgO (111) surfaces by 0.89 and 1.17 eV. Therefore, the reaction activity of the AgO (111) surface is larger than that of the AgO (202) surface regardless of H2O or OH precovering. Therefore, the activity improves with an increase in AgO (111) surface area, which is accordance with our experiment results. 4. CONCLUSIONS We present, for the first time, a facile and efficient process for the synthesis of AgO exposed with different planes by potentionstatic deposition. The oxygen evolution performance of the AgO is largely related to the crystal plane. A superior performance of the AgO crystals with mainly {111} exposed faces is observed in electrochemical water oxidation compared with AgO crystals with mainly {202} exposed faces. And the catalytic activity of the AgO crystals with mainly {111} exposed faces can rival the state-of-art Ag-based catalysts, reaching 3.7 mA cm−2 for OER with Tafel slopes of 77 mV dec−1. The reaction mechanism is investigated and the computational results are consistent with our experiment results. This work provides the first study on how to adjust metal-oxide faces in situ for the electrochemical evolution of oxygen. We believe that this study could be adapted to prepare other semiconductor materials with special planes, which may have promising applications in electrocatalytic water splitting.



ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI:xxx. The calculation detail of surface energy and free energy; The mean current density curves with error bars; XRD patterns of AgO after electrolysis; XRD, SEM images and current-density plots of AgO prepared in KNO3 and CH3COOK; Comparison of the OER performance of the AgO with other reported electrocatalysts prepared in situ. AUTHOR INFORMATION Corresponding Author Qiang Zhao; E-mail address: [email protected](Q. Zhao). Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS The authors gratefully acknowledge financial support from the National Natural Science Foundation of China (No. 21878202, 21476153), the Research Project Supported by Shanxi Scholarship Council of China (No. 2017-041), the Natural Science Foundation of Shanxi Province (No. 201801D121052), and the Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi. REFERENCE


Page 18 of 25

Page 19 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(1) Eisenberg, R. Rethinking water splitting. Science 2009, 324, 44-45. (2) Indra, A.; Menezes, P. W.; Sahraie, N. R.; Bergmann, A.; Das, C.; Tallarida, M.; Schmeisser, D.; Strasser, P.; Driess, M. Unification of catalytic water oxidation and oxygen reduction reactions: amorphous beat crystalline cobalt iron oxides. J. Am. Chem. Soc. 2014, 136, 17530-6. (3) Cook, T. R.; Dogutan, D. K.; Reece, S. Y.; Surendranath, Y.; Teets, T. S.; Nocera, D. G. Solar energy supply and storage for the legacy and nonlegacy worlds. Chem. Rev. 2010, 110, 6474-6502. (4) Trotochaud, L.; Young, S. L.; Ranney, J. K.; Boettcher, S. W. Nickel-iron oxyhydroxide oxygen-evolution electrocatalysts: the role of intentional and incidental iron incorporation. J. Am. Chem. Soc. 2014, 136, 6744-53. (5) Kanan, M. W.; Nocera, D. G. In situ formation of an oxygen-evolving catalyst in neutral water containing phosphate and Co2+. Science 2008, 321, 1072-5. (6) Irshad, A.; Munichandraiah, N. An oxygen evolution Co-Ac catalyst--the synergistic effect of phosphate ions. Phy. Chem. Chem. Phys. 2014, 16, 5412-22. (7) Wang, X.; Zhuang, L.; He, T.; Jia, Y.; Zhang, L.; Yan, X.; Gao, M.; Du, A.; Zhu, Z.; Yao, X.; Yu, S. H. Grafting cobalt diselenide on defective graphene for enhanced oxygen evolution reaction. iScience 2018, 7, 145-153. (8) Dinca, M.; Surendranath, Y.; Nocera, D. G. Nickel-borate oxygen-evolving catalyst that functions under benign conditions. P. Natl. Acad. Sci. Usa. 2010, 107, 10337-10341.



(9) Risch, M.; Klingan, K.; Heidkamp, J.; Ehrenberg, D.; Chernev, P.; Zaharieva, I.; Dau, H. Nickel-oxido structure of a water-oxidizing catalyst film. Chemi. Commun. 2011, 47, 11912-11914. (10) Chen, Z.; Meyer, T. J. Copper(II) catalysis of water oxidation. Angew. Chem. 2013, 52, 700-3. (11) Du, J.; Chen, Z.; Ye, S.; Wiley, B. J.; Meyer, T. J. Copper as a robust and transparent electrocatalyst for water oxidation. Angew. Chem. 2015, 54, 2073-8. (12) Zhao, Q.; Hao, G.; Yuan, W.; Ma, N.; Li, J. Novel copper oxides oxygen evolving catalyst in situ for electrocatalytic water splitting. Electrochim. Acta 2015, 152, 280-285. (13) Wu, Y.; Chen, M.; Han, Y.; Luo, H.; Su, X.; Zhang, M. T.; Lin, X.; Sun, J.; Wang, L.; Deng, L. Fast and simple preparation of iron-based thin films as highly efficient water-oxidation catalysts in neutral aqueous solution. Angew. Chem., Int. Ed. 2015, 54, 4870-4875. (14) Zhao, Q.; Li, D.; Gao, G.; Yuan, W.; Hao, G.; Li, J. Nanostructured Fe(III) catalysts for water oxidation assembled with the aid of organic acid salt electrolytes. Appl. Surf. Sci. 2016, 387, 1274-1280. (15) Zhao, Q.; Li, D.; Gao, G.; Yuan, W.; Hao, G.; Li, J. Nanostructured iron(III) oxide catalyst electrodeposited from Fe(II) triflate for electrocatalytic water oxidation. Int. J. Hydrogen Energ 2016, 41, 17193-17198. (16) Wang, W.; Zhao, Q.; Dong, J.; Li, J. A novel silver oxides oxygen evolving catalyst for water splitting. Int. J. Hydrogen Energ 2011, 36, 7374-7380.


Page 20 of 25

Page 21 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(17) Zhao, Q.; Yu, Z.; Yuan, W.; Li, J. Metal-Ci oxygen-evolving catalysts generated in situ in a mild H2O/CO2 environment. Int. J. Hydrogen Energ 2013, 38, 5251-5258. (18) Zhao, Q.; Yu, Z.; Yuan, W.; Li, J. A WO3/Ag–Bi oxygen-evolution catalyst for splitting water under mild conditions. Int. J. Hydrogen Energ 2012, 37, 13249-13255. (19) Zhao, Q.; Yu, Z.; Hao, G.; Yuan, W.; Li, J. Modulated crystalline Ag-Ci oxygen-evolving catalysts for electrocatalytic water oxidation. Int. J. Hydrogen Energ 2014, 39, 1364-1370. (20) Feng, L. L.; Yu, G.; Wu, Y.; Li, G. D.; Li, H.; Sun, Y.; Asefa, T.; Chen, W.; Zou, X. High-index faceted Ni3S2 nanosheet arrays as highly active and ultrastable electrocatalysts for water splitting. J. Am. Chem. Soc. 2015, 137, 14023-6. (21) Chen, L.; Su, Y.; Chen, S.; Li, N.; Bao, L.; Li, W.; Wang, Z.; Wang, M.; Wu, F. Hierarchical

Li1.2Ni0.2Mn0.6O2

nanoplates

with

exposed

{010}

planes

as

high-performance cathode material for lithium-ion batteries. Adv. Mater. 2014, 26, 6756-60. (22) Su, D.; Dou, S.; Wang, G. Single crystalline Co3O4 nanocrystals exposed with different crystal planes for Li-O2 batteries. Sci. Rep. 2014, 4, 5767. (23) Bu, L.; Zhang, N.; Guo, S.; Zhang, X.; Li, J.; Yao, J.; Wu, T.; Lu, G.; Ma, J.-Y.; Su, D. Biaxially strained PtPb/Pt core/shell nanoplate boosts oxygen reduction catalysis. Science 2016, 354, 1410-1414. (24) Liu, G.; Yang, H. G.; Pan, J.; Yang, Y. Q.; Lu, G. Q.; Cheng, H. M. Titanium dioxide crystals with tailored facets. Chem. Rev. 2014, 114, 9559-612.



(25) Wang, X.; Zhuang, L.; Jia, Y.; Liu, H.; Yan, X.; Zhang, L.; Yang, D.; Zhu, Z.; Yao, X. Plasma-triggered synergy of exfoliation, phase transformation, and surface engineering in cobalt diselenide for enhanced water oxidation. Angew. Chem. 2018, 57, 16421-16425. (26) Li, D.; Wei, C.; Wang, Q.; Liu, L.; Zhong, D.; Hao, G.; Li, J.; Zhao, Q. In-situ ammonia-modulated silver oxide as efficient oxygen evolution catalyst in neutral organic carboxylate buffer. Int. J. Hydrogen Energ 2018, 43, 14379-14387. (27) Kresse, G.; Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 1996, 54, 11169-11186. (28) Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 1994, 50, 17953-17979. (29) Kresse, G.; Hafner, J. Ab initio molecular dynamics for liquid metals. Phys. Rev. B 1993, 47, 558-561. (30) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 1996, 77, 3865. (31) Henkelman, G.; Uberuaga, B. P.; Jónsson, H. A climbing image nudged elastic band method for finding saddle points and minimum energy paths. J. Chem. Phys. 2000, 113, 9901-9904. (32) Scatturin, V.; Bellon, P. L.; Salkind, A. J. The Structure of Silver Oxide Determined by Means of Neutron Diffraction. J. Electrochem. Soc. 1961, 108, 819-822.


Page 22 of 25

Page 23 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(33) Mikhlin, Y. L.; Vishnyakova, E. A.; Romanchenko, A. S.; Saikova, S. V.; Likhatski, M. N.; Larichev, Y. V.; Tuzikov, F. V.; Zaikovskii, V. I.; Zharkov, S. M. Oxidation of Ag nanoparticles in aqueous media: Effect of particle size and capping. Appl. Surf. Sci. 2014, 297, 75-83. (34) Parayil, S. K.; Razzaq, A.; Park, S.-M.; Kim, H. R.; Grimes, C. A.; In, S.-I. Photocatalytic conversion of CO2 to hydrocarbon fuel using carbon and nitrogen co-doped sodium titanate nanotubes. Appl. Catal. A-Gen. 2015, 498, 205-213. (35) Wang, H.; Li, J.; Huo, P.; Yan, Y.; Guan, Q. Preparation of Ag2O/Ag2CO3/MWNTs composite photocatalysts for enhancement of ciprofloxacin degradation. Appl. Surf. Sci. 2016, 366, 1-8. (36) Kumar, R. Mixed phase lamellar titania-titanate anchored with Ag2O and polypyrrole for enhanced adsorption and photocatalytic activity. J. Colloid Interf. Sci. 2016, 477, 83-93. (37) Evans, M. G.; Polanyi, M. Inertia and driving force of chemical reactions. T. Faraday Soc. 1938, 34, 11-24. (38) Liu, S.; White, M. G.; Liu, P. Mechanism of oxygen reduction reaction on pt(111) in alkaline solution: importance of chemisorbed water on surface. J. Phys. Chem. C 2016, 120, 15288-15298. (39) Liu, S.; White, M. G.; Liu, P. Oxygen reduction reaction on Ag(111) in alkaline solution: a combined density functional theory and kinetic monte carlo study. ChemCatChem 2018, 10, 540-549.



(40) Jia, Y.; Zhang, L.; Du, A.; Gao, G.; Chen, J.; Yan, X.; Brown, C. L.; Yao, X. Defect graphene as a trifunctional catalyst for electrochemical reactions. Adv. Mater. 2016, 28, 9532-9538. (41) Valdés, Á.; Qu, Z. W.; Kroes, G. J.; Rossmeisl, J.; Nørskov, J. K. Oxidation and photo-oxidation of water on TiO2 surface. J. Phys. Chem. C 2008, 112, 9872-9879.


Page 24 of 25

Page 25 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC Graphic


Oxygen-Evolution on in-Situ Selective Formation ... - ACS Publications

Recommend Documents