Gold Doping in a Layered Co‐Ni Hydroxide System via Galvanic Replacement for Overall Electrochemical Water Splitting

Abstract

The development of active yet stable bifunctional materials to produce hydrogen and oxygen via electrochemical water splitting is an ongoing challenge. Here, a system based on electrodeposited Ni(OH) 2 and Co(OH) 2 containing highly distributed gold nanoparticles at less than 0.25 at% to facilitate the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under alkaline conditions is developed. The key aspect is using galvanic replacement to deposit gold on a layer of electrodeposited Co(OH) 2 prior to electrodepositing Ni(OH) 2 . The fabrication of a composite system based on Co(OH) 2 -Au-Ni(OH) 2 is required for optimal activity for both the HER and OER. The composite is characterized with helium ion microscopy, transmission electron microscopy, depth profiling X-ray photoelectron microscopy, and a variety of electrochemical techniques. This material exceeds the activity of Pt for the HER at current densities greater than 40 mA cm −2 and is stable for both reactions for prolonged periods of electrolysis. In a two-electrode configuration, current densities greater than 175 mA cm −2 for overall water splitting could be readily achieved at an applied voltage of 1.90 V in a commercially relevant electrolyte of 6 m NaOH.

Electrochemically Fabricated Ni−P, Ni−S and Ni−Se Materials for Overall Water Splitting: Investigating the Concept of Bifunctional Electrocatalysis

“…[36] In the case of pristine NiSe x some metallic Ni is evident from the peak at 853 eV (Figure 7b1), though the intensity is less than that observed for the NiP x film (Figure 6b1). The multicomponent peaks seen over the range of 855 to 865 eV are consistent with Ni in the + 2 oxidation state (Ni(OH) 2 and NiO as seen for the previous examples and the presence of NiSe x material. [37] For Se the doublet is comprised of peaks at 53.6 and 54.4 eV which correspond to Se 3d 5/2 and Se 3d 3/2 respectively.…”

“…The Ni 2p and O 1s spectra are consistent with the presence of Ni in a + 2 and + 3 oxidation state such as NiO, Ni(OH) 2 and NiOOH [27] with also some evidence in the O 1s spectrum of surface bound H 2 O groups as evidenced by the peak at higher binding energy. The surface morphology of NiS x , was then investigated by SEM (Figure 5a) to get another insight into the change in the HER performance after the OER.…”

Electrochemically Fabricated Ni−P, Ni−S and Ni−Se Materials for Overall Water Splitting: Investigating the Concept of Bifunctional Electrocatalysis

“…[36] In the case of pristine NiSe x some metallic Ni is evident from the peak at 853 eV (Figure 7b1), though the intensity is less than that observed for the NiP x film (Figure 6b1). The multicomponent peaks seen over the range of 855 to 865 eV are consistent with Ni in the + 2 oxidation state (Ni(OH) 2 and NiO as seen for the previous examples and the presence of NiSe x material. [37] For Se the doublet is comprised of peaks at 53.6 and 54.4 eV which correspond to Se 3d 5/2 and Se 3d 3/2 respectively.…”

“…The Ni 2p and O 1s spectra are consistent with the presence of Ni in a + 2 and + 3 oxidation state such as NiO, Ni(OH) 2 and NiOOH [27] with also some evidence in the O 1s spectrum of surface bound H 2 O groups as evidenced by the peak at higher binding energy. The surface morphology of NiS x , was then investigated by SEM (Figure 5a) to get another insight into the change in the HER performance after the OER.…”

Harnessing Native Iron Ore as an Efficient Electrocatalyst for Overall Water Splitting

“…The optimised mass loading of the catalyst onto the glassy carbon electrode was initially investigated for the best OER performance (Figure a). As with many metal oxide catalysts the performance improved with potential cycling . Notably however, only 5 cycles were required to activate the catalyst for the best OER performance (Figure S2) which is significantly less when compared to a previous study on a Gibeon meteorite that required 20 h of ageing for optimal performance .…”

Metallic Gold-Incorporated Ni(OH)2 for Enhanced Water Oxidation in an Alkaline Medium: A Simple Wet-Chemical Approach

“…Similar types of spin–orbit coupling peaks are observed for Au-Ni­(OH) 2 (2) with binding energies of 529.85, 531.08, and 533.18 eV, which are ascribed to the metal oxide, oxygen from hydroxyl groups, and surface-adsorbed water molecules, respectively. Au XPS spectra given in Figure S1 reveal the presence of one maximum at a binding energy of 87.2 eV, which implies the presence of gold in the metallic state . Further confirmation of Ni 3+ in metallic gold-incorporated Ni­(OH) 2 was made via electron paramagnetic resonance (EPR) spectroscopy (Figure ), and it can be observed that the intensity of a peak at a g value of 2.05 increased abruptly in the case of Au-Ni­(OH) 2 compared to Ni­(OH) 2 , inferring the increase of Ni 3+ concentration after gold incorporation …”

Electrochemically Fabricated Ni−P, Ni−S and Ni−Se Materials for Overall Water Splitting: Investigating the Concept of Bifunctional Electrocatalysis

“…[36] In the case of pristine NiSe x some metallic Ni is evident from the peak at 853 eV (Figure 7b1), though the intensity is less than that observed for the NiP x film (Figure 6b1). The multicomponent peaks seen over the range of 855 to 865 eV are consistent with Ni in the + 2 oxidation state (Ni(OH) 2 and NiO as seen for the previous examples and the presence of NiSe x material. [37] For Se the doublet is comprised of peaks at 53.6 and 54.4 eV which correspond to Se 3d 5/2 and Se 3d 3/2 respectively.…”

“…The Ni 2p and O 1s spectra are consistent with the presence of Ni in a + 2 and + 3 oxidation state such as NiO, Ni(OH) 2 and NiOOH [27] with also some evidence in the O 1s spectrum of surface bound H 2 O groups as evidenced by the peak at higher binding energy. The surface morphology of NiS x , was then investigated by SEM (Figure 5a) to get another insight into the change in the HER performance after the OER.…”

Harnessing Native Iron Ore as an Efficient Electrocatalyst for Overall Water Splitting

“…The optimised mass loading of the catalyst onto the glassy carbon electrode was initially investigated for the best OER performance (Figure a). As with many metal oxide catalysts the performance improved with potential cycling . Notably however, only 5 cycles were required to activate the catalyst for the best OER performance (Figure S2) which is significantly less when compared to a previous study on a Gibeon meteorite that required 20 h of ageing for optimal performance .…”

Metallic Gold-Incorporated Ni(OH)2 for Enhanced Water Oxidation in an Alkaline Medium: A Simple Wet-Chemical Approach

“…Similar types of spin–orbit coupling peaks are observed for Au-Ni­(OH) 2 (2) with binding energies of 529.85, 531.08, and 533.18 eV, which are ascribed to the metal oxide, oxygen from hydroxyl groups, and surface-adsorbed water molecules, respectively. Au XPS spectra given in Figure S1 reveal the presence of one maximum at a binding energy of 87.2 eV, which implies the presence of gold in the metallic state . Further confirmation of Ni 3+ in metallic gold-incorporated Ni­(OH) 2 was made via electron paramagnetic resonance (EPR) spectroscopy (Figure ), and it can be observed that the intensity of a peak at a g value of 2.05 increased abruptly in the case of Au-Ni­(OH) 2 compared to Ni­(OH) 2 , inferring the increase of Ni 3+ concentration after gold incorporation …”

Electrochemically Fabricated Ni−P, Ni−S and Ni−Se Materials for Overall Water Splitting: Investigating the Concept of Bifunctional Electrocatalysis

“…[36] In the case of pristine NiSe x some metallic Ni is evident from the peak at 853 eV (Figure 7b1), though the intensity is less than that observed for the NiP x film (Figure 6b1). The multicomponent peaks seen over the range of 855 to 865 eV are consistent with Ni in the + 2 oxidation state (Ni(OH) 2 and NiO as seen for the previous examples and the presence of NiSe x material. [37] For Se the doublet is comprised of peaks at 53.6 and 54.4 eV which correspond to Se 3d 5/2 and Se 3d 3/2 respectively.…”

“…The Ni 2p and O 1s spectra are consistent with the presence of Ni in a + 2 and + 3 oxidation state such as NiO, Ni(OH) 2 and NiOOH [27] with also some evidence in the O 1s spectrum of surface bound H 2 O groups as evidenced by the peak at higher binding energy. The surface morphology of NiS x , was then investigated by SEM (Figure 5a) to get another insight into the change in the HER performance after the OER.…”

Harnessing Native Iron Ore as an Efficient Electrocatalyst for Overall Water Splitting

“…The optimised mass loading of the catalyst onto the glassy carbon electrode was initially investigated for the best OER performance (Figure a). As with many metal oxide catalysts the performance improved with potential cycling . Notably however, only 5 cycles were required to activate the catalyst for the best OER performance (Figure S2) which is significantly less when compared to a previous study on a Gibeon meteorite that required 20 h of ageing for optimal performance .…”

Metallic Gold-Incorporated Ni(OH)2 for Enhanced Water Oxidation in an Alkaline Medium: A Simple Wet-Chemical Approach

“…Similar types of spin–orbit coupling peaks are observed for Au-Ni­(OH) 2 (2) with binding energies of 529.85, 531.08, and 533.18 eV, which are ascribed to the metal oxide, oxygen from hydroxyl groups, and surface-adsorbed water molecules, respectively. Au XPS spectra given in Figure S1 reveal the presence of one maximum at a binding energy of 87.2 eV, which implies the presence of gold in the metallic state . Further confirmation of Ni 3+ in metallic gold-incorporated Ni­(OH) 2 was made via electron paramagnetic resonance (EPR) spectroscopy (Figure ), and it can be observed that the intensity of a peak at a g value of 2.05 increased abruptly in the case of Au-Ni­(OH) 2 compared to Ni­(OH) 2 , inferring the increase of Ni 3+ concentration after gold incorporation …”