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Additively manufactured 316L stainless steel: An efficient electrocatalyst
international journal of hydrogen energy xxx (xxxx) xxx
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Short Communication
Additively manufactured 316L stainless steel: An efficient electrocatalyst M.J.K. Lodhi a, K.M. Deen b, Waseem Haider a,* a b
School of Engineering and Technology, Central Michigan University, Mt. Pleasant, MI, 48859, USA Department of Materials Engineering, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
highlights Etched AM 316L stainless steel manifested enhanced catalytic activity for OER. The etched AM 316L manifested 310 mV overpotential at 10 mA/cm2. The effective surface area of the AM sample was increased after etching. The etched AM presented stable OER potential for 100 h at 10 mA/cm2.
article info
abstract
Article history:
In the quest of finding an economical, yet efficient material, the idea of fabricating 316L
Received 15 April 2019
stainless steel using additive manufacturing technology was explored to produce material
Received in revised form
with refined sub-granular structure. The surface of the stainless steel was further chemi-
18 July 2019
cally treated with an etching solution to expose the grain boundaries. The grain boundary
Accepted 29 July 2019
enriched surface resulted in more active sites for the oxygen evolution reaction (OER) in
Available online xxx
additively manufactured treated (AM-T) 316L stainless steel. AM-T sample manifests enhanced catalytic activity for OER with an overpotential of 310 mV to draw a 10 mA/cm2
Keywords:
current density, along with a lower Tafel slope of 42 mV/dec compared to AM and wrought
Additive manufacturing
samples. These features were validated from the increased double-layer capacitance of
Stainless steel
AM-T and approximately 1.5 times larger electrochemically effective surface area of AM-T
OER
due to etching treatment compared to the wrought sample. Furthermore, AM-T also pos-
Overpotential
sesses stable activity retention for 100 h at a current density of 10 mA/cm2. © 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction The global demand for energy is increasing due to rapid industrialization and population growth. The resources available for meeting the energy requirements are mostly
fossil fuels e.g. natural gas, coal, and oil [1]. The replacement of these existing resources and environment-friendly fuel is tantalizing searched. Among the various candidates, hydrogen as a fuel has been the center of attention, because it is environment-friendly and the resources for its production
* Corresponding author. E-mail address: [email protected] (W. Haider). https://doi.org/10.1016/j.ijhydene.2019.07.217 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Lodhi MJK et al., Additively manufactured 316L stainless steel: An efficient electrocatalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.07.217
2
international journal of hydrogen energy xxx (xxxx) xxx
are virtually inexhaustible [2]. Out of the different methods for the production of hydrogen, electrochemical water splitting is considered as the most impressive [3,4]. Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are the two primary half-cell reactions occur during electrochemical water splitting [5,6]. OER is more sluggish in nature, compare to HER due to the requirement of four protons reduction by the transfer of four electrons from the catalytic surface [7,8]. Thus, the search for efficient, stable and economical OER catalyst is the pursuit of water splitting reaction. Recent studies have shown the focus on 3d-transition metal i.e. Fe and Ni-based catalysts with high efficiency and catalytic stability [9e11]. When there is the use of nickel and iron-based catalysts, it is straightforward to think about stainless steel as a candidate material for this purpose. Stainless steel is a low-cost alloy containing iron and nickel, thus possessing intrinsic OER activity, but with mediocre catalytic performance. Literature suggested the use of different chemical, electrochemical and hydrothermal treatments to enhance the catalytic efficiency of stainless steel [12e15]. Various reports also suggest the use of stainless steel foam, as an electrocatalyst for OER, due to its large electrochemically active area [16,17]. However, stainless steel foam produced by conventional processes have limitations of nonuniform fiber discontinuity and the presence of large cavities. Furthermore, the mechanical properties of stainless steel foams are also very inferior that restrict its use in extreme and harsh environments [17]. Additive manufacturing of metals is a very nascent process that provides the flexibility of design and allows the manufacturing of controlled porous structures. In addition to the design flexibility, the very high cooling rate intrinsic to this process develops a very non-conventional microstructure with very refined sub-grains confined within the larger grains [18,19]. In this work, we employed additive manufacturing to fabricate 316L stainless steel electrodes and chemically treated the surface to use as an OER catalyst.
Experimental details
further chemically treated by etching in an acidic solution containing 15 ml hydrochloric acid, 10 ml nitric acid, 10 ml acetic acid and 3 drops of glycerol for 35 s followed by rinsing in deionized water. Due to chemical treatment of the AM samples, the grain and subgrain boundaries were revealed on the surface and that was believed to endow the sample with useful functionalities in terms of OER activity. This chemically treated AM sample will be referred as AM-T in further discussion.
Microstructural characterization Microstructural analysis for both the wrought and AM samples were carried out via scanning electron microscope (SEM) (Hitachi S-3400-II). The samples were ground till 1200 grit size, followed by fine polishing using 3 and 1 mm diamond suspension, sequentially. The samples were etched in a similar manner as mentioned in the above section. For electron backscatter diffraction (EBSD) the samples were ion milled.
Electrochemical characterization A three-electrode electrochemical cell was used for electrochemical characterization in 1 M KOH solution. Wrought, AM and AM-T samples were used as working electrodes with an exposed surface area of 1.26 cm2. Graphite rod and Hg/HgO were used as counter and reference electrodes, respectively. All the potential values reported in this study are with respect to the reversible hydrogen electrode (RHE). Linear sweep voltammetry curves were recorded between 0 and 1 V vs. reference electrode at a scan speed of 5 mV/s, and a positive feedback mode was applied for I-R compensation. Electrochemical impedance spectra were recorded at the onset potential of OER (constant DC potential) as evaluated from the linear sweep voltammetry of all the samples within 100 kHz to 1 Hz frequency range. The chronopotentiometry curve for AMT was obtained at a current density of 10 mA/cm2. The cyclic galvanostatic test was performed at a current density of 10 mA/cm2 for 15 min followed by 15 min delay at OCP. This was one cycle (15 min galvanostatic followed by 15 min OCP) and 100 cycles were performed.
Materials Additively manufactured (AM) 316L stainless steel samples were fabricated from gas atomized 316L stainless steel powder (particle size 15e45 mm) using selective laser melting process. Renishaw AM 250 unit was used to fabricate the samples (circular disks of 15.2 mm diameter and 5 mm thickness) at a laser power of 200 W, keeping a layer thickness of 30 mm and a hatch spacing of 100 mm. Wrought 316L stainless steel (circular rod of 15.2 mm diameter) was purchased from “Onlinemetals®” and cut into 5 mm thick disk samples, using a high speed saw.
Surface preparation The surface of both the wrought and AM samples were ground using silicon carbide (SiC) papers from 180 to 1200 grit size under running water stream, followed by ultrasonication in ethanol and rinsing in deionized water. AM samples were
Results & discussion Microstructure The grain distribution and grain orientation of the samples were assessed using electron backscatter diffraction (EBSD) using a scanning electron microscope (Fig. 1). Wrought sample (Fig. 1a) exhibited the typical faceted morphology (polygonal grains), whereas the AM samples exhibited the elongated grains in the build direction (Fig. 1b). The width of the elongated grains in the AM sample is its finest dimension that is comparatively finer than the wrought sample. The elongated structure of the grains in the AM sample is due to the heat removal through the build plate during the solidification process. A continuous change in color within each grain was observed for the AM sample, depicting the continuous variation in the orientation. Furthermore, the AM sample reveled a
Please cite this article as: Lodhi MJK et al., Additively manufactured 316L stainless steel: An efficient electrocatalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.07.217
international journal of hydrogen energy xxx (xxxx) xxx
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Fig. 1 e EBSD IPF color map with inverse pole figure (Red 001, Green 101 and Blue 111) for (a) wrought and (b) AM samples. Scale bars for ‘a’ is 200 mm and ‘b’ is 100 mm. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)
varying grain size distribution. Therefore, the EBSD data suggests that AM sample showed a very non-conventional grain shape, orientation, and size. Furthermore, the SEM micrographs of the mechanically polished and chemically etched surfaces of both the wrought and AM samples are presented in Fig. 2. The wrought sample showed sharp grain boundaries with an equiaxed grain structure (Fig. 2a) [20]. Twin bands were also evident in the wrought sample, possibly associated with prior mechanical processing. However, AM sample revealed a very nonconventional and heterogeneous microstructure due to rapid solidification, under anisotropic heat removal (Fig. 2b and c). Of all the different features, cellular structure (Fig. 2c) present in the AM samples is of particular interest. The average size of the cellular structure present in the AM sample was approximately 800 nm. The development and size of these cellular structures are associated with the rapid solidification (inherited to additive manufacturing process). Therefore, the geometry of this cellular subgranular structure is related to the laser processing parameters. The earlier report proved the boundaries of these cellular structures to be concentrated with dislocations [21]. The development of these high dislocation densities in AM sample is because of the thermal contraction stresses, because of rapid solidification. The dislocation densities, corresponds to large stored energies, resulting in active areas in the material [22].
conversion devices with 10% efficiency [23]. AM-T required an overpotential (ɳ) of only 310 mV to achieve the current density of 10 mA/cm2, however, wrought and AM samples demonstrated a comparatively higher overpotential of 367 and
Electrocatalytic properties The electrocatalytic activity of the chemically treated additively manufactured (AM-T) 316L stainless steel was investigated in 1 M KOH solution. For comparison purpose, AM and wrought 316L stainless steel (mechanically polished up to 1200 grit size) were also studied. Fig. 3a shows the linear sweep voltammetry (LSV) curves of the samples for OER. In comparison with wrought (1550 mV vs. RHE) and AM (1540 mV vs. RHE), AM-T exhibited a noticeable lower onset potential (1490 mV vs. RHE), suggesting its remarkable electrocatalytic activity and being more desirable for OER. The current density of 10 mA/cm2 has been envisioned as a standard to study the electrocatalytic efficiency of the electrocatalyst, as this is the amount of current density expected for solar to fuel
Fig. 2 e SEM image for etched (a) wrought and (b, c) AM samples.
Please cite this article as: Lodhi MJK et al., Additively manufactured 316L stainless steel: An efficient electrocatalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.07.217
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Fig. 3 e (a) Linear sweep voltammetry (Polarization curves) of AM-T, AM and wrought samples (b) Tafel plots for OER over AM-T, AM and wrought samples, (c) Electrochemical impedance spectroscopy curves for AM-T, AM and wrought samples, (d) Chronopotentiometric curve for AM-T at a current density of 10 mA/cm2.
340 mV respectively, to draw the same amount of current density. The value of overpotential for wrought 316L stainless steel confirmed the values reported in the literature [24]. This overpotential needed for AM-T is also comparable or lower than the NiFeOx (310 mV), CoFeOx (370 mV), NiCoOx (380 mV) and CuxCoyO4 (390 mV) multi-metal electrocatalysts under similar conditions [23,25]. However, the overpotential for AMT is comparable to IrO2 based catalysts (310 mV) [26], which is considered as a benchmark electrocatalyst for OER in alkaline solution. This clearly confirmed the value-added transformation to the stainless steel using additive manufacturing approach and subsequent chemical treatment, making it comparable to precious metal-based electrocatalysts. It is worth mentioning here that the perspective of revealing the grain and subgranular structure in AM material through chemical etching phenomenon, proved worthy of enhanced catalytic activity. The superior catalytic activity of the AM-T sample has been attributed to its microstructure, constituting the subgranular structure. Such subgrain boundaries are concentrated with dislocations, which provides more active sites for OER to happen. In order to further evaluate the kinetics of OER on AM-T surface, Tafel plots were also obtained, as shown in Fig. 3-b. AM-T showed a lower Tafel slope (42 mV/dec) than that of AM (51 mV/dec) and wrought (56 mV/dec) stainless steel. The lower Tafel slope for AM-T indicated a rapidly increased
current density with a small change in the overpotential that proves it to be more electrochemically active. In AM and wrought stainless steel the OER is considered to be controlled by electron/proton reaction, i.e. adsorption and surmount of activation energy by the OH species to interact with the active sites on the catalyst surface, (S þ OH / SeOH þ e together with S OH / S OH*, where S represents the catalytic active sites). This can be estimated from the Tafel slope of around 60 mV/dec [27]. The relatively high Tafel slopes of AM and wrought samples indicate the slow kinetics of OH species adsorption on the electrocatalytic active sites. In case of AM-T, the electrocatalytic behavior towards oxygen evolution can be determined from the first and second electron/proton transfer reaction (S OH þ OH / S O þ H2O þ e), which is highlighted by the typical Tafel slop of nearly 40 mV/dec [28]. The abovementioned reactions on the surface of wrought, AM and AMT samples, during OER, suggested that the kinetics of OER is enhanced on the surface of AM-T, because of the more grain boundaries. These grain boundaries helps in the activation of the reactants and adsorption process [29,30]. This, once again reflects the enhanced electrocatalytic efficiency of AM-T as that of wrought stainless steel. To gain more insight into the electrocatalytic efficiency of the AM-T, electrochemical impedance spectra were also obtained as represented in Fig. 3-c. Charge transport resistance (Rct) and adsorption resistance (Rads) were calculated from
Please cite this article as: Lodhi MJK et al., Additively manufactured 316L stainless steel: An efficient electrocatalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.07.217
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Table 1 e Kinetic parameters and electrochemically active surface area obtained from the impedance spectra. Samples
R1 (U * cm2)
R2 (U * cm2)
R3 (U * cm2)
Rct (R2R1) (U * cm2)
Rads (R3R1) (U * cm2)
Cdl (mF/cm2)
Effective surface area (cm2)
AM-T AM Wrought
1.27 1.68 1.82
18.30 42.69 66.10
15.72 36.06 60.26
17.03 41.01 64.28
14.45 34.38 58.44
425.7 275.5 273.1
30.1 19.9 19.8
impedance spectra and reported in Table 1. AM-T possess smaller Rct (17.03 U*cm2) compared to AM (41.01 U*cm2) and wrought (64.28 U*cm2) samples, that is indicative of faster charge transport characteristic during electrochemical reaction for AM-T sample [31]. AM-T also showed lower Rads (14.45 U*cm2) than that of AM (34.38 U*cm2) and wrought (58.44 U*cm2) samples, suggesting the enhanced surface activity of AM-T sample. The lower Rct and Rads offered by AM-T also supports its facile kinetic behavior, as predicted from lower Tafel slope. The double-layer capacitance Cdl and electrochemically effective surface area (EESA) was measured from the Nyquist plots according to equation (C ¼ εεοA/d) and the calculated values are given in Table 1. The AM and Wrought samples represented almost similar Cdl values (275 mF/cm2). However, relatively large Cdl of AM-T (425.7 mF/ cm2) compared to AM and wrought stainless steel indicated the effectively increased catalytic activity of AM-T for OER after etching treatment. Similarly, the AM-T sample presented almost 1.5 times larger EESA compared to AM and Wrought samples. For the calculation of EESA from Cdl, the dielectric constant (Ɛ) of the passive film present on the stainless steel
and double layer thickness (d) at the interface were assumed to be 15.6 and 0.1 nm, respectively [9,24,31e33]. Besides, electrocatalytic activity of the AM-T, the electrocatalytic stability of the AM-T was also assessed using chronopotentiometry as demonstrated in Fig. 3-d. AM-T showed very good stability over 100 h for driving a current density of 10 mA/cm2. The variation in the potential to drive a constant current during this period was negligible which proved the stable catalytic efficiency of the AM-T sample for extended use. To further estimate the cyclic stability of the AM-T sample at a current density of 10 mA/cm2, the sequence of constant current (galvanostatic polarization) and a delay (15 min) at OCP were repeated 100 times. The total time for the test was approximately 50 h as shown in Fig. 4. The results showed that catalytic performance did not deteriorate, as the fluctuation in the OER potential during the repeated consecutive tests remained constant. Furthermore, the total change in the potential from the first cycle until the last cycle at the aforementioned potential was highly negligible (14 mV). These results again proved that AM-T can retain its stable catalytic activity and does not undergo any degradation during repeated cycles.
Fig. 4 e Cyclic galvanostatic polarization of AM-T stainless steel sample to estimate the OER potential stability. Magnified images (a) cycle 1e5, (b) cycle 21e25, (c) cycle 51e55, (d) cycle 96e100 were also presented. Please cite this article as: Lodhi MJK et al., Additively manufactured 316L stainless steel: An efficient electrocatalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.07.217
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The above-mentioned comparative electrocatalytic oxidation study clearly demonstrates the higher activity registered by the AM-T sample compared to AM and wrought samples. The key point for this enhanced electrocatalytic efficiency registered by AM-T sample has been attributed to the refined microstructural features (sub-grain enriched surface) related to the manufacturing process. Interestingly, the chemical etching process contributed in exposing the subgranular boundary structure at the AM sample. It is considered that these sub-grain boundaries provide a higher degree of active sites for OER and proved to be beneficial for active electrochemical reactions. This suggested the improved catalytic efficiency of AM-T samples, resulting from a combined effect of microstructure evolved during additive manufacturing and exposed grain structure during chemical etching. These results highlighted the beneficial effects of chemical treatment of AM samples towards OER, which is considered an economical material.
Conclusions This work illustrates the merits of performing chemical treatment on an additively manufactured 316L stainless steel, which is an economical catalytic material for OER. We reported that additive manufacturing in combination with post chemical treatment of 316L stainless steel could present lower overpotential (310 mV) towards OER compared to the existing materials. The relatively smaller Tafel slope (42 mV/dec) of AM-T compared to AM and wrought sample indicated the improved kinetics of OER, which is associated with its exposed fine sub-granular structure, which possibly acts as the catalytic sites. This was evident from the ~1.5 times larger EESA of AM-T sample than AM and wrought samples after etching as calculated from the Cdl values obtained from Nyquist plots. The AM-T sample presented considerably enhanced activity and electrocatalytic stability (minor change in potential approximately 14 mV at which OER occurs) during operation for 50 h at 10 mA/cm2 applied current density. The reason for the enhanced catalytic efficiency of AM-T is the exposure of sub-grain structure which, offered active sites for OER.
references
[1] Chu S, Cui Y, Liu N. The path towards sustainable energy. Nat Mater Jan. 2017;16(1):16e22. [2] Demirdoven N, Deutch J, Golden DM. Hybrid cars now, fuel cell cars later. Science Aug. 2004;305(5686):974e6. [3] Zou X, Zhang Y. Noble metal-free hydrogen evolution catalysts for water splitting. Chem Soc Rev 2015;44(15):5148e80. [4] She ZW, Kibsgaard J, Dickens CF, Chorkendorff I, Nørskov JK, Jaramillo TF. Combining theory and experiment in electrocatalysis: insights into materials design. Science 2017;355:6321. [5] Kim JS, Kim B, Kim H, Kang K. Recent progress on multimetal oxide catalysts for the oxygen evolution reaction. Adv Energy Mater 2018;8:11.
[6] Tahir M, et al. Electrocatalytic oxygen evolution reaction for energy conversion and storage: a comprehensive review. Nano Energy 2017;37:136e57. [7] Hunter BM, Gray HB, Mu¨ller AM. Earth-abundant heterogeneous water oxidation catalysts. Chem Rev 2016;116(22):14120e36. [8] Suen NT, Hung SF, Quan Q, Zhang N, Xu YJ, Chen HM. Electrocatalysis for the oxygen evolution reaction: recent development and future perspectives. Chem Soc Rev 2017;46(2):337e65. [9] Gong M, Dai H. A mini review of NiFe-based materials as highly active oxygen evolution reaction electrocatalysts. Nano Res 2015;8(1):23e39. [10] Kim JS, et al. Amorphous cobalt phyllosilicate with layered crystalline motifs as water oxidation catalyst. Adv Mater 2017;29(21). € fer H, Chatenet M. Steel: the resurrection of a forgotten [11] Scha water-splitting catalyst. ACS Energy Lett 2018;3(3):574e91. € fer H, et al. Stainless steel made to rust: a robust water[12] Scha splitting catalyst with benchmark characteristics. Energy Environ Sci 2015;8(9):2685e97. € fer H, et al. Surface oxidation of stainless steel: oxygen [13] Scha evolution electrocatalysts with high catalytic activity. ACS Catal 2015;5(4):2671e80. [14] Anantharaj S, Venkatesh M, Salunke AS, Simha TVSV, Prabu V, Kundu S. High-performance oxygen evolution anode from stainless steel via controlled surface oxidation and Cr removal. ACS Sustain Chem Eng 2017;5(11):10072e83. [15] Moureaux F, Stevens P, Toussaint G, Chatenet M. Development of an oxygen-evolution electrode from 316L stainless steel: application to the oxygen evolution reaction in aqueous lithium-air batteries. J Power Sources 2013;229:123e32. [16] Anantharaj S, et al. Stainless steel scrubber: a cost efficient catalytic electrode for full water splitting in alkaline medium. ACS Sustain Chem Eng 2018;6(2):2498e509. [17] Huang X, Chang S, Lee WSV, Ding J, Xue JM. Threedimensional printed cellular stainless steel as a high-activity catalytic electrode for oxygen evolution. J Mater Chem A 2017;5(34):18176e82. € nnar LE, Koptyug A, Olse n J, Saeidi K, Shen Z. Hierarchical [18] Ra structures of stainless steel 316L manufactured by Electron Beam Melting. Addit Manuf Oct. 2017;17:106e12. [19] Lodhi MJK, Deen KM, Haider W. Corrosion behavior of additively manufactured 316L stainless steel in acidic media. Materialia Oct. 2018;2:111e21. [20] Lodhi MJK, Deen KM, Greenlee-wacker MC, Haider W. Additively manufactured 316L stainless steel with improved corrosion resistance and biological response for biomedical applications. Addit Manuf 2019;27(January):8e19. [21] Wang YM, et al. Additively manufactured hierarchical stainless steels with high strength and ductility. Nat Mater 2017. M. Additive manufacturing of [22] Gorsse S, Hutchinson C, Goune metals : a brief review of the characteristic microstructures and properties of steels, Ti-6Al-4V and high-entropy alloys. Sci Technol Adv Mater 2017;18(1):584e610. [23] McCrory CCL, Jung S, Peters JC, Jaramillo TF. Benchmarking heterogeneous electrocatalysts for the oxygen evolution reaction. J Am Chem Soc 2013;135(45):16977e87. [24] Yu F, Li F, Sun L. Stainless steel as an efficient electrocatalyst for water oxidation in alkaline solution. Int J Hydrogen Energy 2016;41(10):5230e3. [25] Grewe T, Deng X, Weidenthaler C, Schu¨th F, Tu¨ysu¨z H. Design of ordered mesoporous composite materials and their electrocatalytic activities for water oxidation. Chem Mater 2013;25(24):4926e35.
Please cite this article as: Lodhi MJK et al., Additively manufactured 316L stainless steel: An efficient electrocatalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.07.217
international journal of hydrogen energy xxx (xxxx) xxx
[26] Liu Y, et al. Corrosion engineering towards efficient oxygen evolution electrodes with stable catalytic activity for over 6000 hours. Nat Commun 2018;9(1). [27] Park J, Sa YJ, Baik H, Kwon T, Joo SH, Lee K. Iridium-based multimetallic Nanoframe@Nanoframe structure: an efficient and robust electrocatalyst toward oxygen evolution reaction. ACS Nano 2017;11(6):5500e9. [28] Burke MS, Kast MG, Trotochaud L, Smith AM, Boettcher SW. Cobalt-iron (Oxy)hydroxide oxygen evolution electrocatalysts: the role of structure and composition on activity, stability, and mechanism. J Am Chem Soc 2015;137(10):3638e48. [29] Song F, Hu X. Exfoliation of layered double hydroxides for enhanced oxygen evolution catalysis. Nat Commun 2014;5. [30] Tang C, et al. Spatially confined hybridization of nanometersized NiFe hydroxides into nitrogen-doped graphene
7
frameworks leading to superior oxygen evolution reactivity. Adv Mater 2015;27(30):4516e22. [31] Wang T, et al. Enhanced electrocatalytic activity for hydrogen evolution reaction from self-assembled mono dispersed molybdenum sulfide nanoparticles on an Au electrode. Energy Environ Sci 2013;6(2):625e33. [32] Mohammadi M, et al. Electrochemical and passive layer characterizations of 304L, 316L, and duplex 2205 stainless steels in thiosulfate gold leaching solutions. J Electrochem Soc 2016;163(14):C883e94. [33] Zhang K, et al. Three-dimensional interconnected MoS2 nanosheets on industrial 316L stainless steel mesh as an efficient hydrogen evolution electrode. Int J Hydrogen Energy 2019;44(3):1555e64.
Please cite this article as: Lodhi MJK et al., Additively manufactured 316L stainless steel: An efficient electrocatalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.07.217
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Short Communication
Additively manufactured 316L stainless steel: An efficient electrocatalyst M.J.K. Lodhi a, K.M. Deen b, Waseem Haider a,* a b
School of Engineering and Technology, Central Michigan University, Mt. Pleasant, MI, 48859, USA Department of Materials Engineering, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
highlights Etched AM 316L stainless steel manifested enhanced catalytic activity for OER. The etched AM 316L manifested 310 mV overpotential at 10 mA/cm2. The effective surface area of the AM sample was increased after etching. The etched AM presented stable OER potential for 100 h at 10 mA/cm2.
article info
abstract
Article history:
In the quest of finding an economical, yet efficient material, the idea of fabricating 316L
Received 15 April 2019
stainless steel using additive manufacturing technology was explored to produce material
Received in revised form
with refined sub-granular structure. The surface of the stainless steel was further chemi-
18 July 2019
cally treated with an etching solution to expose the grain boundaries. The grain boundary
Accepted 29 July 2019
enriched surface resulted in more active sites for the oxygen evolution reaction (OER) in
Available online xxx
additively manufactured treated (AM-T) 316L stainless steel. AM-T sample manifests enhanced catalytic activity for OER with an overpotential of 310 mV to draw a 10 mA/cm2
Keywords:
current density, along with a lower Tafel slope of 42 mV/dec compared to AM and wrought
Additive manufacturing
samples. These features were validated from the increased double-layer capacitance of
Stainless steel
AM-T and approximately 1.5 times larger electrochemically effective surface area of AM-T
OER
due to etching treatment compared to the wrought sample. Furthermore, AM-T also pos-
Overpotential
sesses stable activity retention for 100 h at a current density of 10 mA/cm2. © 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction The global demand for energy is increasing due to rapid industrialization and population growth. The resources available for meeting the energy requirements are mostly
fossil fuels e.g. natural gas, coal, and oil [1]. The replacement of these existing resources and environment-friendly fuel is tantalizing searched. Among the various candidates, hydrogen as a fuel has been the center of attention, because it is environment-friendly and the resources for its production
* Corresponding author. E-mail address: [email protected] (W. Haider). https://doi.org/10.1016/j.ijhydene.2019.07.217 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Lodhi MJK et al., Additively manufactured 316L stainless steel: An efficient electrocatalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.07.217
2
international journal of hydrogen energy xxx (xxxx) xxx
are virtually inexhaustible [2]. Out of the different methods for the production of hydrogen, electrochemical water splitting is considered as the most impressive [3,4]. Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are the two primary half-cell reactions occur during electrochemical water splitting [5,6]. OER is more sluggish in nature, compare to HER due to the requirement of four protons reduction by the transfer of four electrons from the catalytic surface [7,8]. Thus, the search for efficient, stable and economical OER catalyst is the pursuit of water splitting reaction. Recent studies have shown the focus on 3d-transition metal i.e. Fe and Ni-based catalysts with high efficiency and catalytic stability [9e11]. When there is the use of nickel and iron-based catalysts, it is straightforward to think about stainless steel as a candidate material for this purpose. Stainless steel is a low-cost alloy containing iron and nickel, thus possessing intrinsic OER activity, but with mediocre catalytic performance. Literature suggested the use of different chemical, electrochemical and hydrothermal treatments to enhance the catalytic efficiency of stainless steel [12e15]. Various reports also suggest the use of stainless steel foam, as an electrocatalyst for OER, due to its large electrochemically active area [16,17]. However, stainless steel foam produced by conventional processes have limitations of nonuniform fiber discontinuity and the presence of large cavities. Furthermore, the mechanical properties of stainless steel foams are also very inferior that restrict its use in extreme and harsh environments [17]. Additive manufacturing of metals is a very nascent process that provides the flexibility of design and allows the manufacturing of controlled porous structures. In addition to the design flexibility, the very high cooling rate intrinsic to this process develops a very non-conventional microstructure with very refined sub-grains confined within the larger grains [18,19]. In this work, we employed additive manufacturing to fabricate 316L stainless steel electrodes and chemically treated the surface to use as an OER catalyst.
Experimental details
further chemically treated by etching in an acidic solution containing 15 ml hydrochloric acid, 10 ml nitric acid, 10 ml acetic acid and 3 drops of glycerol for 35 s followed by rinsing in deionized water. Due to chemical treatment of the AM samples, the grain and subgrain boundaries were revealed on the surface and that was believed to endow the sample with useful functionalities in terms of OER activity. This chemically treated AM sample will be referred as AM-T in further discussion.
Microstructural characterization Microstructural analysis for both the wrought and AM samples were carried out via scanning electron microscope (SEM) (Hitachi S-3400-II). The samples were ground till 1200 grit size, followed by fine polishing using 3 and 1 mm diamond suspension, sequentially. The samples were etched in a similar manner as mentioned in the above section. For electron backscatter diffraction (EBSD) the samples were ion milled.
Electrochemical characterization A three-electrode electrochemical cell was used for electrochemical characterization in 1 M KOH solution. Wrought, AM and AM-T samples were used as working electrodes with an exposed surface area of 1.26 cm2. Graphite rod and Hg/HgO were used as counter and reference electrodes, respectively. All the potential values reported in this study are with respect to the reversible hydrogen electrode (RHE). Linear sweep voltammetry curves were recorded between 0 and 1 V vs. reference electrode at a scan speed of 5 mV/s, and a positive feedback mode was applied for I-R compensation. Electrochemical impedance spectra were recorded at the onset potential of OER (constant DC potential) as evaluated from the linear sweep voltammetry of all the samples within 100 kHz to 1 Hz frequency range. The chronopotentiometry curve for AMT was obtained at a current density of 10 mA/cm2. The cyclic galvanostatic test was performed at a current density of 10 mA/cm2 for 15 min followed by 15 min delay at OCP. This was one cycle (15 min galvanostatic followed by 15 min OCP) and 100 cycles were performed.
Materials Additively manufactured (AM) 316L stainless steel samples were fabricated from gas atomized 316L stainless steel powder (particle size 15e45 mm) using selective laser melting process. Renishaw AM 250 unit was used to fabricate the samples (circular disks of 15.2 mm diameter and 5 mm thickness) at a laser power of 200 W, keeping a layer thickness of 30 mm and a hatch spacing of 100 mm. Wrought 316L stainless steel (circular rod of 15.2 mm diameter) was purchased from “Onlinemetals®” and cut into 5 mm thick disk samples, using a high speed saw.
Surface preparation The surface of both the wrought and AM samples were ground using silicon carbide (SiC) papers from 180 to 1200 grit size under running water stream, followed by ultrasonication in ethanol and rinsing in deionized water. AM samples were
Results & discussion Microstructure The grain distribution and grain orientation of the samples were assessed using electron backscatter diffraction (EBSD) using a scanning electron microscope (Fig. 1). Wrought sample (Fig. 1a) exhibited the typical faceted morphology (polygonal grains), whereas the AM samples exhibited the elongated grains in the build direction (Fig. 1b). The width of the elongated grains in the AM sample is its finest dimension that is comparatively finer than the wrought sample. The elongated structure of the grains in the AM sample is due to the heat removal through the build plate during the solidification process. A continuous change in color within each grain was observed for the AM sample, depicting the continuous variation in the orientation. Furthermore, the AM sample reveled a
Please cite this article as: Lodhi MJK et al., Additively manufactured 316L stainless steel: An efficient electrocatalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.07.217
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Fig. 1 e EBSD IPF color map with inverse pole figure (Red 001, Green 101 and Blue 111) for (a) wrought and (b) AM samples. Scale bars for ‘a’ is 200 mm and ‘b’ is 100 mm. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)
varying grain size distribution. Therefore, the EBSD data suggests that AM sample showed a very non-conventional grain shape, orientation, and size. Furthermore, the SEM micrographs of the mechanically polished and chemically etched surfaces of both the wrought and AM samples are presented in Fig. 2. The wrought sample showed sharp grain boundaries with an equiaxed grain structure (Fig. 2a) [20]. Twin bands were also evident in the wrought sample, possibly associated with prior mechanical processing. However, AM sample revealed a very nonconventional and heterogeneous microstructure due to rapid solidification, under anisotropic heat removal (Fig. 2b and c). Of all the different features, cellular structure (Fig. 2c) present in the AM samples is of particular interest. The average size of the cellular structure present in the AM sample was approximately 800 nm. The development and size of these cellular structures are associated with the rapid solidification (inherited to additive manufacturing process). Therefore, the geometry of this cellular subgranular structure is related to the laser processing parameters. The earlier report proved the boundaries of these cellular structures to be concentrated with dislocations [21]. The development of these high dislocation densities in AM sample is because of the thermal contraction stresses, because of rapid solidification. The dislocation densities, corresponds to large stored energies, resulting in active areas in the material [22].
conversion devices with 10% efficiency [23]. AM-T required an overpotential (ɳ) of only 310 mV to achieve the current density of 10 mA/cm2, however, wrought and AM samples demonstrated a comparatively higher overpotential of 367 and
Electrocatalytic properties The electrocatalytic activity of the chemically treated additively manufactured (AM-T) 316L stainless steel was investigated in 1 M KOH solution. For comparison purpose, AM and wrought 316L stainless steel (mechanically polished up to 1200 grit size) were also studied. Fig. 3a shows the linear sweep voltammetry (LSV) curves of the samples for OER. In comparison with wrought (1550 mV vs. RHE) and AM (1540 mV vs. RHE), AM-T exhibited a noticeable lower onset potential (1490 mV vs. RHE), suggesting its remarkable electrocatalytic activity and being more desirable for OER. The current density of 10 mA/cm2 has been envisioned as a standard to study the electrocatalytic efficiency of the electrocatalyst, as this is the amount of current density expected for solar to fuel
Fig. 2 e SEM image for etched (a) wrought and (b, c) AM samples.
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Fig. 3 e (a) Linear sweep voltammetry (Polarization curves) of AM-T, AM and wrought samples (b) Tafel plots for OER over AM-T, AM and wrought samples, (c) Electrochemical impedance spectroscopy curves for AM-T, AM and wrought samples, (d) Chronopotentiometric curve for AM-T at a current density of 10 mA/cm2.
340 mV respectively, to draw the same amount of current density. The value of overpotential for wrought 316L stainless steel confirmed the values reported in the literature [24]. This overpotential needed for AM-T is also comparable or lower than the NiFeOx (310 mV), CoFeOx (370 mV), NiCoOx (380 mV) and CuxCoyO4 (390 mV) multi-metal electrocatalysts under similar conditions [23,25]. However, the overpotential for AMT is comparable to IrO2 based catalysts (310 mV) [26], which is considered as a benchmark electrocatalyst for OER in alkaline solution. This clearly confirmed the value-added transformation to the stainless steel using additive manufacturing approach and subsequent chemical treatment, making it comparable to precious metal-based electrocatalysts. It is worth mentioning here that the perspective of revealing the grain and subgranular structure in AM material through chemical etching phenomenon, proved worthy of enhanced catalytic activity. The superior catalytic activity of the AM-T sample has been attributed to its microstructure, constituting the subgranular structure. Such subgrain boundaries are concentrated with dislocations, which provides more active sites for OER to happen. In order to further evaluate the kinetics of OER on AM-T surface, Tafel plots were also obtained, as shown in Fig. 3-b. AM-T showed a lower Tafel slope (42 mV/dec) than that of AM (51 mV/dec) and wrought (56 mV/dec) stainless steel. The lower Tafel slope for AM-T indicated a rapidly increased
current density with a small change in the overpotential that proves it to be more electrochemically active. In AM and wrought stainless steel the OER is considered to be controlled by electron/proton reaction, i.e. adsorption and surmount of activation energy by the OH species to interact with the active sites on the catalyst surface, (S þ OH / SeOH þ e together with S OH / S OH*, where S represents the catalytic active sites). This can be estimated from the Tafel slope of around 60 mV/dec [27]. The relatively high Tafel slopes of AM and wrought samples indicate the slow kinetics of OH species adsorption on the electrocatalytic active sites. In case of AM-T, the electrocatalytic behavior towards oxygen evolution can be determined from the first and second electron/proton transfer reaction (S OH þ OH / S O þ H2O þ e), which is highlighted by the typical Tafel slop of nearly 40 mV/dec [28]. The abovementioned reactions on the surface of wrought, AM and AMT samples, during OER, suggested that the kinetics of OER is enhanced on the surface of AM-T, because of the more grain boundaries. These grain boundaries helps in the activation of the reactants and adsorption process [29,30]. This, once again reflects the enhanced electrocatalytic efficiency of AM-T as that of wrought stainless steel. To gain more insight into the electrocatalytic efficiency of the AM-T, electrochemical impedance spectra were also obtained as represented in Fig. 3-c. Charge transport resistance (Rct) and adsorption resistance (Rads) were calculated from
Please cite this article as: Lodhi MJK et al., Additively manufactured 316L stainless steel: An efficient electrocatalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.07.217
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Table 1 e Kinetic parameters and electrochemically active surface area obtained from the impedance spectra. Samples
R1 (U * cm2)
R2 (U * cm2)
R3 (U * cm2)
Rct (R2R1) (U * cm2)
Rads (R3R1) (U * cm2)
Cdl (mF/cm2)
Effective surface area (cm2)
AM-T AM Wrought
1.27 1.68 1.82
18.30 42.69 66.10
15.72 36.06 60.26
17.03 41.01 64.28
14.45 34.38 58.44
425.7 275.5 273.1
30.1 19.9 19.8
impedance spectra and reported in Table 1. AM-T possess smaller Rct (17.03 U*cm2) compared to AM (41.01 U*cm2) and wrought (64.28 U*cm2) samples, that is indicative of faster charge transport characteristic during electrochemical reaction for AM-T sample [31]. AM-T also showed lower Rads (14.45 U*cm2) than that of AM (34.38 U*cm2) and wrought (58.44 U*cm2) samples, suggesting the enhanced surface activity of AM-T sample. The lower Rct and Rads offered by AM-T also supports its facile kinetic behavior, as predicted from lower Tafel slope. The double-layer capacitance Cdl and electrochemically effective surface area (EESA) was measured from the Nyquist plots according to equation (C ¼ εεοA/d) and the calculated values are given in Table 1. The AM and Wrought samples represented almost similar Cdl values (275 mF/cm2). However, relatively large Cdl of AM-T (425.7 mF/ cm2) compared to AM and wrought stainless steel indicated the effectively increased catalytic activity of AM-T for OER after etching treatment. Similarly, the AM-T sample presented almost 1.5 times larger EESA compared to AM and Wrought samples. For the calculation of EESA from Cdl, the dielectric constant (Ɛ) of the passive film present on the stainless steel
and double layer thickness (d) at the interface were assumed to be 15.6 and 0.1 nm, respectively [9,24,31e33]. Besides, electrocatalytic activity of the AM-T, the electrocatalytic stability of the AM-T was also assessed using chronopotentiometry as demonstrated in Fig. 3-d. AM-T showed very good stability over 100 h for driving a current density of 10 mA/cm2. The variation in the potential to drive a constant current during this period was negligible which proved the stable catalytic efficiency of the AM-T sample for extended use. To further estimate the cyclic stability of the AM-T sample at a current density of 10 mA/cm2, the sequence of constant current (galvanostatic polarization) and a delay (15 min) at OCP were repeated 100 times. The total time for the test was approximately 50 h as shown in Fig. 4. The results showed that catalytic performance did not deteriorate, as the fluctuation in the OER potential during the repeated consecutive tests remained constant. Furthermore, the total change in the potential from the first cycle until the last cycle at the aforementioned potential was highly negligible (14 mV). These results again proved that AM-T can retain its stable catalytic activity and does not undergo any degradation during repeated cycles.
Fig. 4 e Cyclic galvanostatic polarization of AM-T stainless steel sample to estimate the OER potential stability. Magnified images (a) cycle 1e5, (b) cycle 21e25, (c) cycle 51e55, (d) cycle 96e100 were also presented. Please cite this article as: Lodhi MJK et al., Additively manufactured 316L stainless steel: An efficient electrocatalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.07.217
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The above-mentioned comparative electrocatalytic oxidation study clearly demonstrates the higher activity registered by the AM-T sample compared to AM and wrought samples. The key point for this enhanced electrocatalytic efficiency registered by AM-T sample has been attributed to the refined microstructural features (sub-grain enriched surface) related to the manufacturing process. Interestingly, the chemical etching process contributed in exposing the subgranular boundary structure at the AM sample. It is considered that these sub-grain boundaries provide a higher degree of active sites for OER and proved to be beneficial for active electrochemical reactions. This suggested the improved catalytic efficiency of AM-T samples, resulting from a combined effect of microstructure evolved during additive manufacturing and exposed grain structure during chemical etching. These results highlighted the beneficial effects of chemical treatment of AM samples towards OER, which is considered an economical material.
Conclusions This work illustrates the merits of performing chemical treatment on an additively manufactured 316L stainless steel, which is an economical catalytic material for OER. We reported that additive manufacturing in combination with post chemical treatment of 316L stainless steel could present lower overpotential (310 mV) towards OER compared to the existing materials. The relatively smaller Tafel slope (42 mV/dec) of AM-T compared to AM and wrought sample indicated the improved kinetics of OER, which is associated with its exposed fine sub-granular structure, which possibly acts as the catalytic sites. This was evident from the ~1.5 times larger EESA of AM-T sample than AM and wrought samples after etching as calculated from the Cdl values obtained from Nyquist plots. The AM-T sample presented considerably enhanced activity and electrocatalytic stability (minor change in potential approximately 14 mV at which OER occurs) during operation for 50 h at 10 mA/cm2 applied current density. The reason for the enhanced catalytic efficiency of AM-T is the exposure of sub-grain structure which, offered active sites for OER.
references
[1] Chu S, Cui Y, Liu N. The path towards sustainable energy. Nat Mater Jan. 2017;16(1):16e22. [2] Demirdoven N, Deutch J, Golden DM. Hybrid cars now, fuel cell cars later. Science Aug. 2004;305(5686):974e6. [3] Zou X, Zhang Y. Noble metal-free hydrogen evolution catalysts for water splitting. Chem Soc Rev 2015;44(15):5148e80. [4] She ZW, Kibsgaard J, Dickens CF, Chorkendorff I, Nørskov JK, Jaramillo TF. Combining theory and experiment in electrocatalysis: insights into materials design. Science 2017;355:6321. [5] Kim JS, Kim B, Kim H, Kang K. Recent progress on multimetal oxide catalysts for the oxygen evolution reaction. Adv Energy Mater 2018;8:11.
[6] Tahir M, et al. Electrocatalytic oxygen evolution reaction for energy conversion and storage: a comprehensive review. Nano Energy 2017;37:136e57. [7] Hunter BM, Gray HB, Mu¨ller AM. Earth-abundant heterogeneous water oxidation catalysts. Chem Rev 2016;116(22):14120e36. [8] Suen NT, Hung SF, Quan Q, Zhang N, Xu YJ, Chen HM. Electrocatalysis for the oxygen evolution reaction: recent development and future perspectives. Chem Soc Rev 2017;46(2):337e65. [9] Gong M, Dai H. A mini review of NiFe-based materials as highly active oxygen evolution reaction electrocatalysts. Nano Res 2015;8(1):23e39. [10] Kim JS, et al. Amorphous cobalt phyllosilicate with layered crystalline motifs as water oxidation catalyst. Adv Mater 2017;29(21). € fer H, Chatenet M. Steel: the resurrection of a forgotten [11] Scha water-splitting catalyst. ACS Energy Lett 2018;3(3):574e91. € fer H, et al. Stainless steel made to rust: a robust water[12] Scha splitting catalyst with benchmark characteristics. Energy Environ Sci 2015;8(9):2685e97. € fer H, et al. Surface oxidation of stainless steel: oxygen [13] Scha evolution electrocatalysts with high catalytic activity. ACS Catal 2015;5(4):2671e80. [14] Anantharaj S, Venkatesh M, Salunke AS, Simha TVSV, Prabu V, Kundu S. High-performance oxygen evolution anode from stainless steel via controlled surface oxidation and Cr removal. ACS Sustain Chem Eng 2017;5(11):10072e83. [15] Moureaux F, Stevens P, Toussaint G, Chatenet M. Development of an oxygen-evolution electrode from 316L stainless steel: application to the oxygen evolution reaction in aqueous lithium-air batteries. J Power Sources 2013;229:123e32. [16] Anantharaj S, et al. Stainless steel scrubber: a cost efficient catalytic electrode for full water splitting in alkaline medium. ACS Sustain Chem Eng 2018;6(2):2498e509. [17] Huang X, Chang S, Lee WSV, Ding J, Xue JM. Threedimensional printed cellular stainless steel as a high-activity catalytic electrode for oxygen evolution. J Mater Chem A 2017;5(34):18176e82. € nnar LE, Koptyug A, Olse n J, Saeidi K, Shen Z. Hierarchical [18] Ra structures of stainless steel 316L manufactured by Electron Beam Melting. Addit Manuf Oct. 2017;17:106e12. [19] Lodhi MJK, Deen KM, Haider W. Corrosion behavior of additively manufactured 316L stainless steel in acidic media. Materialia Oct. 2018;2:111e21. [20] Lodhi MJK, Deen KM, Greenlee-wacker MC, Haider W. Additively manufactured 316L stainless steel with improved corrosion resistance and biological response for biomedical applications. Addit Manuf 2019;27(January):8e19. [21] Wang YM, et al. Additively manufactured hierarchical stainless steels with high strength and ductility. Nat Mater 2017. M. Additive manufacturing of [22] Gorsse S, Hutchinson C, Goune metals : a brief review of the characteristic microstructures and properties of steels, Ti-6Al-4V and high-entropy alloys. Sci Technol Adv Mater 2017;18(1):584e610. [23] McCrory CCL, Jung S, Peters JC, Jaramillo TF. Benchmarking heterogeneous electrocatalysts for the oxygen evolution reaction. J Am Chem Soc 2013;135(45):16977e87. [24] Yu F, Li F, Sun L. Stainless steel as an efficient electrocatalyst for water oxidation in alkaline solution. Int J Hydrogen Energy 2016;41(10):5230e3. [25] Grewe T, Deng X, Weidenthaler C, Schu¨th F, Tu¨ysu¨z H. Design of ordered mesoporous composite materials and their electrocatalytic activities for water oxidation. Chem Mater 2013;25(24):4926e35.
Please cite this article as: Lodhi MJK et al., Additively manufactured 316L stainless steel: An efficient electrocatalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.07.217
international journal of hydrogen energy xxx (xxxx) xxx
[26] Liu Y, et al. Corrosion engineering towards efficient oxygen evolution electrodes with stable catalytic activity for over 6000 hours. Nat Commun 2018;9(1). [27] Park J, Sa YJ, Baik H, Kwon T, Joo SH, Lee K. Iridium-based multimetallic Nanoframe@Nanoframe structure: an efficient and robust electrocatalyst toward oxygen evolution reaction. ACS Nano 2017;11(6):5500e9. [28] Burke MS, Kast MG, Trotochaud L, Smith AM, Boettcher SW. Cobalt-iron (Oxy)hydroxide oxygen evolution electrocatalysts: the role of structure and composition on activity, stability, and mechanism. J Am Chem Soc 2015;137(10):3638e48. [29] Song F, Hu X. Exfoliation of layered double hydroxides for enhanced oxygen evolution catalysis. Nat Commun 2014;5. [30] Tang C, et al. Spatially confined hybridization of nanometersized NiFe hydroxides into nitrogen-doped graphene
7
frameworks leading to superior oxygen evolution reactivity. Adv Mater 2015;27(30):4516e22. [31] Wang T, et al. Enhanced electrocatalytic activity for hydrogen evolution reaction from self-assembled mono dispersed molybdenum sulfide nanoparticles on an Au electrode. Energy Environ Sci 2013;6(2):625e33. [32] Mohammadi M, et al. Electrochemical and passive layer characterizations of 304L, 316L, and duplex 2205 stainless steels in thiosulfate gold leaching solutions. J Electrochem Soc 2016;163(14):C883e94. [33] Zhang K, et al. Three-dimensional interconnected MoS2 nanosheets on industrial 316L stainless steel mesh as an efficient hydrogen evolution electrode. Int J Hydrogen Energy 2019;44(3):1555e64.
Please cite this article as: Lodhi MJK et al., Additively manufactured 316L stainless steel: An efficient electrocatalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.07.217