recycling

Article Water Electrolysis Anode Based on 430 Stainless Steel Coated with Cobalt Recycled from Li-Ion Batteries

Eric M. Garcia * and Hosane A. Taroco

Department of Exact and Biological Sciences, University of São João Del Rei—Sete Lagoas Campus, Sete Lagoas 35701-970, Brazil; [email protected] * Correspondence: [email protected]; Tel./Fax: +55-31-3697-2003



Received: 4 August 2018; Accepted: 4 September 2018; Published: 6 September 2018


Abstract: In this paper, a new environmentally-friendly anode for hydrogen production was developed based on 430 stainless steel with an electrodeposited cobalt layer. The novelty of this work is the cobalt source once the electrodeposition bath was obtained from acid dissolution of a spent Li-ion battery cathode. The oxygen evolution reaction on electrodeposited cobalt in 1 M KOH is compatible with the E. Kobussen mechanism. The water discharge is related with reaction determinant step in low overpotential. The cobalt electrodeposition (3 Ccm−2) promotes a significant improvement of 430 stainless steel anodic properties for oxygen evolution reaction. When the overpotential reaches 370 mV, the density current for 430 stainless steel with electrodeposit cobalt is 19 mA·cm−2 against 0.80 mA·cm−2 for 430 stainless steel without cobalt. Thus, the anode construction described in this paper is an excellent option for Li-ion battery recycling.

Keywords: Li-ion batteries; anode; cobalt recycling

1. Introduction Renewable energy source such as hydrogen is considered crucial for a more sustainable future [1]. In fact, since daily processes even space exploration will depend, largely of hydrogen production within few years [2]. The hydrogen is considered environmentally friendly once the reaction between H2 with O2 molecules (forward direction in Equation (1)) has only water molecules as a sub-product, beyond high molar enthalpy value (∆H = 285.8 kJ/mol at 1013 mbar and 298 K) [2]. In this context, the water electrolysis is the most attractive route among the existed processes for very pure hydrogen production (and also O2) in large scale (inverse direction in Equation (1)) [1].

H2(g) +1/2O2(g) → H2O(g) ∆H = 285.8 kJ/mol (1)

In water electrolysis, the overpotential for oxygen evolution reaction (OER) is a limiting factor and responsible for the greatest energy loss source when the electrolysis is performed in alkaline or acid media [3,4]. However, alkaline media is preferred because in this condition the catalysts used in water electrolysis are more active and stable [4]. The OER also is present in others strategic power sources such as aqueous lithium air batteries [5], NiMH [3], and Zn-air [6]. Many papers are dedicated to investigate the alternative anode for OER with high efficiency [7]. The RuO2 and IrO2 are suggested as the benchmark for OER in alkaline solution [8]. However, these oxides have a prohibitive cost for large scale application [8]. Commercial electrodes for water electrolysis at an industrial scale must have important characteristics such as: high conductivity, high corrosion resistance, high catalytic effect for oxygen evolution reaction, and moreover low cost [9]. For Ni foam, the current density for OER is 10 mA·cm−2 in η = 390 mV (vs. NHE) in 0.5 M KOH. When the Ni foam receives a Co layer by electroless deposition (~2.3 µm) the overpotential reduces for 270 mV [10]. This shows that a

Recycling 2018, 3, 42; doi:10.3390/recycling3030042 www.mdpi.com/journal/recycling Recycling 2018, 3, 42 2 of 10 cobalt layer around 2.3 µm is enough to decrease the overvoltage for OER approximately in 100 mV. Although the Ni anode has a good anodic behavior in OER, its cost is still high compared to the other substrates such as stainless steels. The Ni price is 8.66 US$/Kg against 1.64 US$/Kg and 0.450 US$/Kg for 316SS and 430SS, respectively [11]. In this context, a special interest is devoted to stainless steel as anode for OER in alkaline solutions [9]. The literature revels that the 316 stainless steel (316SS) shows a density current of 10 mA·cm−2 in η = 370 mV in 1.0 mol·L−1 KOH [12]. This value is similar to that found for Ni Foam in the same conditions [12]. This is expected since the 316 has 12% of Ni in its composition [13]. The 430SS has little more than 0.75% of Ni in its composition and approximately the same percentage of others alloys elements [13]. The low Ni content makes the 430SS cheaper, however, it is also less active for OER. [13]. Nevertheless, is possible improve the 430SS anodic properties with cobalt electrodeposition. The great advantage of this method is the possibility of cobalt recovery from Li-ion battery recycling [14]. Many papers describe the cobalt recycling from spent Li-ion batteries as a valuable and environmentally-friendly method [14–16]. Moreover, very pure cobalt can be obtained by acidic dissolution of lithium cobalt oxide (LiCoO2) present in spent Li-ion battery cathode [16]. The recycling of LiCoO2 is important, both economically and environmentally [16]. In this paper, we studied the application of 430SS, coated with recycled cobalt, as anode for OER in 1 M KOH solution. The cobalt used was obtained through dissolution of spent cathode of cell phones Li-ion batteries. The electrochemical characterization of this anode was accomplished through cyclic and linear voltammetry and electrochemical impedance spectroscopy (EIS).

2. Material and Methods

2.1. Preparation of Cobalt Electrodeposition Bath

The Li-ion battery used in this paper was chosen based on the LiCoO2 presence as cathodic material [16]. The Li-battery used was of SAMSUNG® model SM-G530 (SANSUNG®, China). The Li-ion battery was manually dismantled and physically separated into their different parts: anode, cathode, steel, separators, and current collectors. The cathode powder was washed with distilled water under agitation to facilitate the detachment of the active material from current collector. The Li-ion battery electrolyte is a nonaqueous solution composed of lithium salts, such as 1 M LiPF6, in alkyl organic carbonates (ethylene, propylene, and dimethyl carbonates) [17]. Thus, the spent cathode was heated at 200 ◦C for 5 h for eliminate the organic carbonates [17]. The active material was filtered and washed with distilled water to remove possible lithium salts such as LiPF6 and LiClO4. The temperature of 40 ◦C degrees was maintained through a thermostatic bath. The recycled powder was dried in air for 24 h. A mass of 250.10 g of positive electrodes was dissolved in an aqueous solution −1 containing 470.00 mL of 3.00 mol·L H2SO4 and 30.00 mL of 30% (v/v)H2O2. The LiCoO2 acidic 3+ dissolution efficiency increases with acid concentration [17–19]. The H2O2 reduces the Co , insoluble in water, to the Co2+, soluble in aqueous solution. This behavior is represented by the chemical equation of the dissolution process (Equation (2)) [18].

2LiCoO2(s) + 2H2O2(aq) + 3H2SO4(aq) → 2CoSO4(aq) + 3/2O2(g) + Li2SO4(aq) + 5H2O(l) (2)

In order to obtain the cobalt electrodeposition bath, the system was maintained under constant magnetic agitation at 80 ◦C for 2 h. The filtration was performed for separation of carbonaceous material and for obtention of cobalt electrodeposition bath. The concentrations of Mn, Ni, and Cu were analyzed with atomic absorption spectrophotometry (AAS) on a Hitachi-Z 8200 and the values were below of detection limit (10−5 mol·L−1). The concentration of Co2+ was adjusted for 1 mol·L−1 and the solid NaOH was used for adjust the pH = 3 [20]. The pH of electrodeposition bath was maintained equal to 3.0 and the cobalt concentration was 1.00 mol·L−1. This high concentration was chosen to increase the electrodeposition efficiency [16–20]. Recycling 2018, 3, 42 3 of 10

2.2. Electrochemical Measurements Electrochemical measurements were made using an IVIUM power supply (Ivium Technologies BV, De Zaale, The Netherlands). The working electrode was made of commercial ferritic stainless steel 430 (430SS). The steel samples were prepared as rectangular foils with a geometric area of 1.00 cm2. Recycling 2018, 3, x 3 of 10 The auxiliary electrode, with an area of 3.75 cm2, was made of platinum. A saturated calomel electrode (SCE)electrode reference (SCE) electrode reference was electrode used. Thewas AC-impedance used. The AC-impedance measurements measurements were carried were out carried over the out 4 −2 frequencyover the rangefrequency of 10 rangeto 10 of 10Hz4 to at the10−2 restHz at potentials. the rest potentials. The Nyqusit The diagrams Nyqusitwere diagrams adjusted were with adjusted the IVIUMSOFT.with the IVIUMSOFT. The conversion The forconversion reversible for hydrogen reversib electrodele hydrogen (RHE) electrode was made (RHE) using was the made Equation using (3) the andEquation the overpotential (3) and the ( ηoverpotential) was calculated (η) was using calculated Equation using (4) [9 ].Equation (4) [9]. E() =E() + (0.059pH + 0.042) (3) E(RHE) = E(SCE) + (0.059pH + 0.042) (3) η=E() + (0.059pH + 0.042) − 1.23V (4) The working electrodes were sanded with 600-grit sandpaper before each measurement and η = E(SCE) + (0.059pH + 0.042) − 1.23V (4) washed with distilled water. All the electrochemical measurements were performed without solution agitation,The working at 25 °C. electrodes The bath were used sanded in cobalt with electrodeposition 600-grit sandpaper was beforeobtained each by measurementacidic dissolution and of washedspent withcathode distilled of Li-ion water. batteries. All the electrochemicalThe potential used measurements for electrodeposition were performed of cobalt without onto 430SS solution was ◦ agitation,−1.0 V. The at 25 chargeC. The density bath usedwas controlled in cobalt electrodepositionin 3 Ccm−2 [9]. The was scanning obtained elec bytron acidic microscope dissolution JEOL ofJXAmodel spent cathode 8900of RL Li-ion (JEOL, batteries. Peabody, The MA, potential USA) was used used for for electrodeposition surface morphology of cobalt observations. onto 430SS The −2 wascobalt−1.0 electrodeposit V. The charge was density characterized was controlled by X-ray in 3 Ccmdiffraction[9]. on The a scanning200 B Rotaflex-Rigaku electron microscope (Rigaku, JEOLTokyo, JXAmodel Japan) 8900with RLCu (JEOL,Kα irradiation, Peabody, a MA,Cu filter, USA) and was scanning used for speed surface of morphology 2°·min−1. observations. The cobalt electrodeposit was characterized by X-ray diffraction on a 200 B Rotaflex-Rigaku (Rigaku, Tokyo,3. Results Japan) and with Discussion Cu Kα irradiation, a Cu filter, and scanning speed of 2◦·min−1.

3.3.1. Results Characterization and Discussion of Electrodeposited Cobalt onto 430SS

3.1. CharacterizationFigure 1 shows of Electrodeposited the cyclic voltammetry Cobalt onto obtained 430SS by electrodeposition of cobalt on 430SS. The starting potential was −0.5 V (rest potential). Sweeping in the direct direction is observed an increase Figure1 shows the cyclic voltammetry obtained by electrodeposition of cobalt on 430SS. of the cathodic current from −1 V. Some studies of cobalt electrodeposition in pH ≥ 4, proposes that The starting potential was −0.5 V (rest potential). Sweeping in the direct direction is observed the mechanism involves the formation of Co(OH)2 and the subsequent reduction of cobalt hydroxide an increase of the cathodic current from −1 V. Some studies of cobalt electrodeposition in pH ≥ 4, to metallic cobalt [17–20]. Considering the pH used in this study (pH = 3), the presence of other proposes that the mechanism involves the formation of Co(OH)2 and the subsequent reduction of cobalt phases, such as Co(OH)2, in the cobalt electrodeposit was not expected [20]. hydroxide to metallic cobalt [17–20]. Considering the pH used in this study (pH = 3), the presence of Figure 2 shows the scanning electron microscopy (SEM) of electrodeposited cobalt. The other phases, such as Co(OH) , in the cobalt electrodeposit was not expected [20]. morphology of electrodeposited2 cobalt is commonly observed in other papers [15,16]. Figure2 shows the scanning electron microscopy (SEM) of electrodeposited cobalt. The morphology of electrodeposited cobalt is commonly observed in other papers [15,16].

150

100 )

-2 50

0 i (mAcm -50

-100

-150 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 E Vs. Hg/HgO (V) sat Figure 1. Figure Cyclic1. Cyclic voltammetry voltammetry of 430SS of 430SS in a in with a with (black (black line) line) and and without without (red (red line) line) electrodeposited electrodeposited cobalt (scan rate 10 mV·s−1). cobalt (scan rate 10 mV·s−1). Recycling 2018, 3, x 4 of 10 Recycling 2018, 3, 42 4 of 10 Recycling 2018, 3, x 4 of 10

Figure 2. SEM of electrodeposited cobalt onto 430SS with magnification 15,000×.

The FigureFigure 3 shows 2. SEM of the electrodeposited X-ray diffraction cobalt of onto 430SS 430SS with with (black magnificationmagnification line) and 15,00015,000×. without×. (red line) electrodeposited cobalt. The XDR was compared with the JCPDS card for cobalt in hexagonal compactThe Figure phase 3(hcp)3 showsshows (no. the the05-0727) X-rayX-ray and diffractiondiffraction face centered ofof 430SS430SS cubic withwith phase (black(black (fcc) line)line)(no. 15 andand-0806). withoutwithout The presence (red(red line)line) of electrodepositedboth hcp and fcc cobalt. cobalt.phases The Thein electrodeposited XDR XDR was was compared compared cobalt with alsowi theth described JCPDSthe JCPDS card in forthecard cobalt liter forature incobalt hexagonal [16–20]. in hexagonal No compact peaks compactphaserelated (hcp) phaseto (no.the (hcp) 05-0727)Co(OH) (no. 2 and05-0727) phase face centeredandwere face observed, centered cubic phase whichcubic (fcc) phasemay (no. (fcc) 15-0806).be an (no. indication 15 The-0806). presence Thethat presence ofthe both cobalt hcp of bothandelectrodeposition fcchcp phases and fcc in phases electrodepositedmechanism in electrodeposited does cobaltnot involves also cobalt described this also intermediate described in the literature in [20]. the liter [16ature–20]. [16–20]. No peaks No related peaks relatedto the Co(OH) to the2 phaseCo(OH) were2 phase observed, were whichobserved, may bewhich an indication may be thatan theindication cobalt electrodepositionthat the cobalt electrodepositionmechanism does notmechanism involves does this intermediatenot involves [this20]. intermediate [20]. fcc[111] hcp [110] fcc[111] hcp [200] hcp [110]

intensity fcc [200] hcp [200] hcp [101] hcp

intensity fcc [200] hcp [101] hcp

20 25 30 35 40 45 50 55 60 65 70 75 80 (2θ) degrees 20 25 30 35 40 45 50 55 60 65 70 75 80 FigureFigure 3.3. X-rayX-ray diffraction (DRX) (DRX) of of 430SS 430SS with with (2 θ(black) (black degrees line line)) and and without without (red (red line) line) electrodeposited electrodeposited cobalt. cobalt.

−1 FigureFigure 3.4 showsX-ray4 shows diffraction the the cyclic cyclic (DRX) voltammetry voltammetry of 430SS with of 430SS (black of 430SS with line) cobaltandwith without cobalt coating (red coating (430SS/Co) line) electrodeposited (430SS/Co) in 1.0 mol in cobalt. ·1.0L mol·L KOH.−1 TheKOH. first The peak first (A1) ispeak due the(A1 formation) is due ofthe Co(OH) formation2 layer ontoof Co(OH) cobalt previously2 layer onto electrodeposited cobalt previously [14,21]. 2+ 3+ −1 Theelectrodeposited peakFigure A 24 isshows related [14,21]. the to cyclic oxidationThe voltammetrypeak of A Co2 is related toof Co430SS todue withoxidation formation cobalt ofcoating ofCo monometallic2+ to(430SS/Co) Co3+ due layered in formation 1.0 mol·L double of 1 2 KOH.hydroxidesmonometallic The (LDH)first layered ontopeak electrodeposited double(A ) is hydroxides due cobaltthe (LDHformation [21].) The onto A 2electrodepositedofcan Co(OH) also is related layer cobalt with onto Co [21].3 Ocobalt4 Theformation Apreviously2 can [ 22also,23 ].is 3+ 4+ electrodeposited [14,21]. The peak A2 is related to oxidation of Co2+ to Co3+ due formation of Therelated peak with A3 is Co relative3O4 formation to electrochemical [22,23]. reactionThe peak related A3 is to relative conversion to electrochemical of Co to Co [reaction14]. The formationrelated to 4+ − monometallicofconversion Co is important of layered Co3+ to because Codouble4+ [14]. in hydroxides alkaline The formation media (LDH theof) ontoCo OER4+ iselectrodeposited generally important involves because cobalt the inOH alkaline[21]. Theadsorption media A2 can the asalso firstOER is relatedstepgenerally (Equation with involves Co (5)).3O4 formation Thus,the OH a−transition adsorption [22,23]. metalThe as peakfirst ion step withA3 is (Equation multiplerelative valencesto (5 )).electrochemical Thus, and a strongtransition reaction bonding metal related power ion with to is 3+ 4+ 4+ conversionmultiple valences of Co toand Co strong [14]. bonding The formation power ofis necessaryCo is important [21]. Equation because (5) in represents alkaline media the adsorption the OER − generallyof OH- by involves charged the transition OH adsorption metal (M n+as) infirst the step hydroxide/oxide (Equation (5)). crystalline Thus, a transition net. metal ion with multiple valences and strong bondingMn+(net) power + OH− (aq)is necessary → MOHn+ [21].(ads) + Equation e− (5) represents the adsorption(5) of OH- by charged transition metal (Mn+) in the hydroxide/oxide crystalline net. Mn+(net) + OH−(aq) → MOHn+(ads) + e− (5) Recycling 2018, 3, 42 5 of 10 necessary [21]. Equation (5) represents the adsorption of OH- by charged transition metal (Mn+) in the hydroxide/oxide crystalline net.

n+ − n+ − M (net) + OH (aq) → MOH (ads) + e (5) Recycling 2018, 3, x 5 of 10

−1 FigureFigure 4. 4.Cyclic Cyclic voltammetry voltammetry of of 430SS 430SS and and 430SS/Co 430SS/Co in in 1 1 mol mol·L·L −1 KOH with different scanscan rates.rates. 3.2. Mechanism of Oxygen Evolution 3.2. Mechanism of Oxygen Evolution Before study the electrochemical behavior of 430SS coated with recycled cobalt as an anode in Before study the electrochemical behavior of 430SS coated with recycled cobalt as an anode in water electrolysis, some theoretical considerations need to be performed [24,25]. The most commonly water electrolysis, some theoretical considerations need to be performed [24,25]. The most commonly proposed OER pathway for Co oxides is due to the E. Kobussen mechanism [24]. For this mechanism, proposed OER pathway for Co oxides is due to the E. Kobussen mechanism [24]. For this mechanism, only the first two steps have significant importance [24,25]. Initially, the hydroxyl ions are absorbed in only the first two steps have significant importance [24,25]. Initially, the hydroxyl ions are absorbed the active sites, where ‘S’ is the non-occupied active sites (Equation (6)). The reaction determining step in the active sites, where ‘S’ is the non-occupied active sites (Equation (6)). The reaction determining (rds) is the water discharge, where ‘SOH’ is the occupied active sites (Equation (7)). If water discharge step (rds) is the water discharge, where ‘SOH’ is the occupied active sites (Equation (7)). If water (Equation (7)) is the rds, the first step (Equation (6)) is in quasi-equilibrium conditions. The anodic and discharge (Equation (7)) is the rds, the first step (Equation (6)) is in quasi-equilibrium conditions. The cathodic current are approximately equals, thus the Nerstian equilibrium can be considered in terms anodic and cathodic current are approximately equals, thus the Nerstian equilibrium can be of occupied (SOH = θ) and non-occupied (S = 1 − θ) sites. The total current (i1) for first step can be considered in terms of occupied (SOH = θ) and non-occupied (S = 1 − θ) sites. The total current (i) represented by Equation (8) where: for first step can be represented by Equation (8) where: F: The Faraday constant. F: The Faraday constant. η: the overpotential. η: the overpotential. k1 and k−1: The direct and inverse velocity constant rate, respectively, for the first step. k1 and k−1: The direct and inverse velocity constant rate, respectively, for the first step. R: The ideal gas constant (8.314 J·mol−1). R: The ideal gas constant (8.314 J·mol−1). T: The absolute temperature (K). T: The absolute temperature (K). α: The symmetry coefficient of charge transfer barrier. α: The symmetry coefficient of charge transfer barrier. → S+OH SOH + e– (6) −←→ − S + OH→ SOH + e (6) SOH + OH SO← + e +H O ← (7) ()η η − → − (8) i =FkSOHθOH+OHe −FkSO +e(1+ − Hθ)eO (7) ← 2 Since the current represented by the Equation (8) is approximately zero, one can obtain the  − [ (1−α)Fη ] −[ αFη ] relation of non-occupied iand1 = occupiedFk1θ OH sitese onRT the electrode− Fk−1(1 surface− θ)e (EquationRT (9)). (8) η  k = OHe (9) (1 − ) k When the ΔH of adsorption varies with surface covered, the Temkin isotherm more appropriately describes the electrochemical interface. To represent coverage-dependent deviations in adsorption free energy from Langmuir conditions (Equation (9)), the covering dependent function rθ is added where r is a coefficient of increase in adsorption energy (Equation (10)) [24,25]. η ∆  = K OHe e (10) (1−) Recycling 2018, 3, 42 6 of 10

Since the current represented by the Equation (8) is approximately zero, one can obtain the relation of non-occupied and occupied sites on the electrode surface (Equation (9)).

θ k1  − [ Fη ] = OH e RT (9) (1 − θ) k−1

When the ∆H of adsorption varies with surface covered, the Temkin isotherm more appropriately describes the electrochemical interface. To represent coverage-dependent deviations in adsorption free energy from Langmuir conditions (Equation (9)), the covering dependent function rθ is added where r is a coefficient of increase in adsorption energy (Equation (10)) [24,25].

0 θ  − [ Fη ] [ −∆G +r ] = K OH e RT e RT (10) (1 − θ) 2

 θ  If one considers a region in which 0.2 < θ < 0.8 the variation of ln 1−θ is much less than that of the term erθ/RT, thus the term in parenthesis in the Equation (10) is practically constant. The function rθ can be given as a function of the overpotential and the concentration of hydroxyl ions (Equations (11) and (12)).

  θ   rθ = ln RT + RTln − ∆G0 + RTlnOH− + Fη (11) (1 − θ)

rθ = K3 + Fη (12)   θ   K = ln RT + RTln − ∆G0 + RTlnOH− 3 (1 − θ) The equation for the rate determining step (rds) can be written as shown in the Equation (13) where δ is a symmetry factor (0 < δ < 1) for the adsorption process, which depends in magnitude and form of the activation energy barrier. Replacing Equation (12) in Equation (13), the Tafel coefficient is obtained for rds considering a possible situation where α = 0.5 and δ = 0.5 (Equation (14)).

 − [ (1−α)Fη ] [ (1−δ)r ] i2Fk2θ OH e RT e RT (13)

 dlni  Fη 2 = (14) dη RT Figure5 compares the linear voltammetry of 430SS and 430SS/Co in a 1.0 mol ·L−1 KOH. The cobalt electrodeposition significantly reduces the onset potential for oxygen evolution reaction (OER). The onset potential for OER onto 430SS occurs around η = 380 mV. By other hand, for 430SS/co the onset potential is around η = 280 mV. The onset potential was compatible with that obtained in the literature for metallic  dlni  cobalt [25]. The Tafel coefficient dη was calculed for both electrode and for 430SS. Only one distinct dlni −1 −1 region was found with dη = 38.94 V (~59 mV·dec ). Considering T = 298 K, this Tafel coefficient agree with rds related with water discharge (Equation (14)). For 430SS/Co, two distinct regions are found in linear voltammetry. The first region agrees with water discharge as rds (59 mV·dec−1). The second region has a Tafel coefficient around 118 mV·dec−1. In this region there is a high degree of coverage of adsorbed species [25]. Thus, the rds for the OER is mainly due to the step described by Equation (6). One can observe that the cobalt electrodeposition (3 Ccm−2) promotes a significant improvement of 430SS anodic properties for OER. When the overpotential reaches 370 mV, the density current for 430SS/Co is 19 mA·cm−2 against 0.80 mA·cm−2 for 430SS. The 430SS/Co exhibits the double of density current to OER if compared with 316SS [9] or Ni foam [12]. Considering the linear voltammetry of metallic cobalt in 1 M KOH, the literature describes a value around 10 mA·cm−2 of density current of OER when the overpotential is around 370 mV [25]. Probably due to a surface area effect, the density current found in this work is approximately double. This shows the advantage of working with cobalt electrodeposition. Recycling 2018, 3, x 7 of 10 Recycling 2018, 3, x 7 of 10 Recycling 2018, 3, 42 7 of 10

118mVdec-1 -3500 430SS -1 -3500 430SS/Co 118mVdec -4000 430SS 430SS/Co -2 -4000 i= 19mAcm -4500 i= 19mAcm-2 ) -450038.94V-1= 59mVdec-1 -2 -5000 ) 38.94V-1= 59mVdec-1 -2 -5000 -5500 -5500 -6000

ln i (mAcm i ln -6000 -6500 ln i (mAcm i ln -6500 -7000 i= 0.8mAcm-2 -7000 370mV -7500 i= 0.8mAcm-2 -7500 370mV 0.26 0.28 0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.26 0.28 0.30 0.32 0.34 0.36 0.38 0.40 0.42 η (V) η (V) Figure 5. Linear voltammetry of 430SS and 430SS/Co in 1 mol·L−1 KOH with scan rate equal to 1 mV·s −1. Figure 5. Linear voltammetry of 430SS and 430SS/Co in 1 mol·L−1 KOH with scan rate equal to 1 mV·s−1. Figure 5. Linear voltammetry of 430SS and 430SS/Co in 1 mol·L−1 KOH with scan rate equal to 1 mV·s−1. 3.3.3.3. ElectrochemicalElectrochemical Performance Performance 3.3. Electrochemical Performance TheThe electrochemical electrochemical interfacialinterfacial processprocess is is better better investigated investigated using using electrochemical electrochemical impedance impedance spectroscopyspectroscopyThe electrochemical (EIS).(EIS). FiguresFigures6 6 and interfacialand7 7 compares compares process thethe is EISEIS better measuresmeasures investigated of 430 430 usingstainless stainless electrochemical steel steel (430SS) (430SS) andimpedance and 430 430stainless stainlessspectroscopy steel steel with with(EIS). recycled recycled Figures metallic metallic6 and 7 cobaltcompares cobalt coating coating the EIS (430SS/Co) measures in of aa 430 1.01.0 molstainlessmol·L·L−−11 KOHsteel (430SS) afterafter cycliccyclic and 430 voltammetrystainless steelstudy. with The recycled R1 is related metallic with cobaltthe resistance coating of (430SS/Co) ionic motion in ain 1.0 the mol·Lsolution−1 KOH bulk, after R2 and cyclic voltammetry study. The R1 is related with the resistance of ionic motion in the solution bulk, R2 and R3 arevoltammetry the polarization study. resistances The R1 is related and Cdl with is a non-ideal the resistance capacitance of ionic of motion double in layer. the solution For EIS bulk,of 430SS R2 and R3 are the polarization resistances and Cdl is a non-ideal capacitance of double layer. For EIS of 430SS (Figure(FigureR3 6are )6) the thethe interface polarizationinterface is is compatiblecompatible resistances withwith and C RandlesRandlesdl is a non-ideal circuit [24]. [ capacitance24]. However, However, of for double for 430SS/Co 430SS/Co layer. (Figure For (Figure EIS 7) of 7the )430SS theLDH LDH(Figure formed formed 6) theonto onto interface electrodeposited electrodeposited is compatible cobalt cobalt with behave behavesRandless as ascircuit a a supercapacitor, [24]. However, thusthus for two two430SS/Co constant-phaseconstant-phase (Figure 7) the elementselementsLDH must mustformed be be taken ontotaken intoelectrodeposited into account account as as shown shown cobalt in in behave Figure Figure7s [721as [21].]. a supercapacitor, thus two constant-phase elements must be taken into account as shown in Figure 7 [21].

Figure 6. Cont. Recycling 2018, 3, 42 8 of 10 Recycling 2018, 3, x 8 of 10 Recycling 2018, 3, x 8 of 10

Figure 6. Electrochemical impedance spectroscopy for 430SS in 1 M KOH and the adjusted electrical circuit. FigureFigure 6. ElectrochemicalElectrochemical impedance spectroscopy for 430SS in 1 M KOH and the adjusted electrical circuit.

FigureFigure 7. Electrochemical 7. Electrochemical impedance impedance spectroscopy spectroscopy for 430SS/Co for 430SS/Co in 1 M KOH in and1 M the KOH adjusted and electricalthe adjusted circuit. Figure 7. Electrochemical impedance spectroscopy for 430SS/Co in 1 M KOH and the adjusted electrical circuit. 4. Conclusionselectrical circuit.

4.4. Conclusions ConclusionsIn this paper, a new anode for hydrogen production was developed based on 430 stainless steel with an electrodeposited cobalt layer. The novelty of this work is the cobalt source once the electrodeposition In this paper, a new anode for hydrogen production was developed based on 430 stainless steel bath isInobtained this paper, of acida new dissolution anode for of hydrogen Li-ion batteries produc spenttion was cathode. developed The electrodeposited based on 430 stainless cobalt in steel 1 M with an electrodeposited cobalt layer. The novelty of this work is the cobalt source once the KOHwith behavesan electrodeposited as supercapacitor. cobalt Considering layer. The the novelt lineary voltammetry of this work in 1 is M KOH,the cobalt when source the overpotential once the electrodeposition bath is obtained of acid dissolution of Li-ion batteries spent cathode. The reacheselectrodeposition 370 mV, the bath anodic is densityobtained current of foracid 430SS/Co dissolution is 19 of mA Li-ion·cm−2 againstbatteries 0.80 spent mA· cmcathode.−2 for 430SS. The electrodeposited cobalt in 1 M KOH behaves as supercapacitor. Considering the linear voltammetry Thus,electrodeposited the anode construction cobalt in 1 M described KOH behaves in this as paper supercapacitor. is an excellent Considering option for Li-ionthe linear battery voltammetry recycling. in 1 M KOH, when the overpotential reaches 370 mV, the anodic density current for 430SS/Co is 19 Futurein 1 M workKOH, must when be the performed overpotential to study reaches the reproducibility 370 mV, the anodic of the OER density catalytic current performance for 430SS/Co once is the 19 mA·cm−2 against 0.80 mA·cm−2 for 430SS. Thus, the anode construction described in this paper is an materialsmA·cm−2 collectedagainst 0.80 from mA·cm spent batteries−2 for 430SS. vary Thus, in composition. the anode construction described in this paper is an excellentexcellent optionoption forfor Li-ionLi-ion batterybattery recycling.recycling. FutureFuture workwork mustmust bebe performedperformed toto studystudy thethe Authorreproducibilityreproducibility Contributions: ofof thetheH.A.T. OEROER and catalyticcatalytic E.M.G. performanceperformance analyzed the data ononcece and thethe prepared materialsmaterials the collected manuscript.collected fromfrom spentspent batteriesbatteries vary in composition. Funding:vary in composition.This work was supported by CNPq, Federal University of São João Del Rei UFSJ/Sete Lagoas/DECEB, UFSJ/DCNAT, Programa de Pós-Graduação Multicêntrico em Química (PPGMQ), and Rede Mineira de Química. Author Contributions: H.A.T. and E.M.G. analyzed the data and prepared the manuscript. ConflictsAuthor Contributions: of Interest: The H.A.T. authors and declare E.M.G. no analyzed conflict ofthe interest. data and prepared the manuscript. Funding: This work was supported by CNPq, Federal University of São João Del Rei UFSJ/Sete Lagoas/DECEB, Funding: This work was supported by CNPq, Federal University of São João Del Rei UFSJ/Sete Lagoas/DECEB, UFSJ/DCNAT, Programa de Pós-Graduação Multicêntrico em Química (PPGMQ), and Rede Mineira de UFSJ/DCNAT, Programa de Pós-Graduação Multicêntrico em Química (PPGMQ), and Rede Mineira de Química. Química. Recycling 2018, 3, 42 9 of 10

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