OER Catalytic Activity Research Articles

Curvature effects on the bifunctional oxygen catalytic performance of single atom metal-N-C.

Understanding the fundamental relationship between the structural information of electrocatalysts and their catalytic activities plays a key role in controlling many important electrochemical processes. Recently, single-atom catalysts (SACs) with the so-called MN4 structure, consisting of a central transition metal quadruply bound to four pyridine nitrogen atoms all situated in an extended carbon-based matrix, have attracted intensive scientific attention owing to their exceptional catalytic performance. In this work, we perform the first-principles density functional theory (DFT) calculations to explore the curvature effects of the carbon matrix surfaces on the catalytic activities for two fundamental electrochemical processes, namely, the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Our DFT results suggest that the curved surface structure can weaken the interaction between the metal atom and the N-doped carbon matrix, modify the electronic structure of the metal atom, and thus increase the adsorption strength of the reaction intermediates, resulting in enhanced OER and ORR catalytic activities of MN4 catalysts. More importantly, a prediction model is developed to evaluate the bifunctional catalytic activities of such catalysts based on their directly obtained parameters including the surface curvature of the catalysts, the number of d electrons of the metal element, and the electronegativity of the metal atom and its coordination atoms in MN4 catalysts. This prediction model not only provides some candidates, for example, FeN4, CoN4 and OsN4 for the ORR; CoN4, NiN4, RuN4, RhN4 and IrN4 for the OER; and CoN4, RuN4, IrN4 and OsN4 for the bifunctional ORR and OER, but also reasonably links the structure of catalysts with their catalytic performance, providing new possibilities for the quick design of high-performance catalysts.

Active-site-enriched Cu-doped Ni–Fe layered double hydroxide nanosheets for boosting the oxygen evolution reaction

In this study, porous Cu-doped NiFe-LDH nanosheets were synthesized through a cation exchange method, and exhibited highly competitive OER catalytic activity and stability.

Zinc and fluorine ions dual-modulated NiCoP nanoprism array electrocatalysts for efficient water splitting

Designing efficient, stable, and low-cost bifunctional catalysts for overall water splitting is significant but challenging. In this work, Zn and F ions co-doped NiCoP nanoprism arrays grown directly on nickel foam (Zn/F-NiCoP/NF) was synthesized via hydrothermal method followed by phosphorization treatment. The resultant Zn/F-NiCoP/NF exhibits high electrocatalytic activity towards hydrogen evolution reaction (HER, η10 = 59 mV) and oxygen evolution reaction (OER, η50 = 285 mV). An alkaline electrolyzer using Zn/F-NiCoP/NF as both cathode and anode requires a low cell voltage of 1.568 V at a current density of 10 mA cm−2 with a high long-term stability of up to 40 h, which outperforms many reported Ni,Co-based catalysts. Density functional theory (DFT) calculations proof that simultaneous doping of NiCoP with Zn and F ions provides flexibility to regulate the electronic configuration and downshifts the transition metal d-band center, thereby optimizing adsorption energy between reactants and intermediates, which enhances the HER and OER catalytic activities. This work highlights that cation–anion co-doping strategy is an effective way to develop highly active transition metal phosphides electrocatalyst for water splitting.

Optimized electroless deposition of NiCoP electrocalysts for enhanced water splitting

Great scientific effort has strived to develop a low-cost and sustainable electrocatalyst with high electrocatalytic activity and long-term stability in the field of water splitting. In this work non-noble metal based NiCoP alloys are burgeoned from catalytic Ni substrates via a facile and eco-friendly electroless deposition method under mild conditions. By appropriately tuning the cobalt content in the chemical bath, we realize NiCoP coatings with tailored Co concentration. The electrochemical investigations of coatings deposited on flat Ni indicate an optimal Co content of 17 at % (Ni0.83Co0.17P) to maximize OER performance. Impressively, the Ni0.83Co0.17P coating deposited on nickel foam exhibits remarkable OER catalytic activity (η = 295 mV at 10 mA cm−2), noteworthy catalytic kinetics (Tafel slope as small as 45 mV dec−1) and high rate of oxygen production for each active site (turnover frequency of 0.16 s−1 at 300 mV) in 1 M KOH. Importantly, the Ni0.83Co0.17P/NF demonstrates excellent long-term stability as inferred by continuous test for 25 h. Furthermore, a full alkaline electrolyzer is designed using Ni0.83Co0.17P/NF as the anode and Pt decorated Ni−P/NF as the cathode, which can drive overall water splitting with a potential as low as 1.60 V at 10 mA cm−2, and also shows outstanding long-term durability.The cheapness of the present preparation method as well as its suitability for large-scale production without the need of expensive raw materials and energy-consuming processes paves the way towards commercial production of transition metal phosphide-based electrocatalysts.

Modulating interfacial charge distribution of NiSe nanoarrays with NiFe-LDH nanosheets for boosting oxygen evolution reaction

Developing efficient, robust non-noble electrodes for the water oxidation in electrocatalytic water splitting is challenging because the physicochemical properties of the electrocatalysts can extremely affect their OER catalytic activity. The interface engineering of materials is promising for modulating the surface properties of catalysts. Herein, vertically aligned NiSe nanoarrays were prepared in situ using a facile solvothermal selenization technique. NiSe@NiFe-LDH nanointerfaces were produced by electrodeposition. The remarkable OER electrocatalytic performance of NiSe@NiFe-LDH heterojunction was evidenced by the overpotentials for driving 100 and 500 mA cm−2, which are only 232 and 302 mV, respectively. Theoretical arithmetic and experimental tests revealed that the prepared electrode possessed high OER catalytic activity, may be ascribed to charge redistribution between the interfaces of NiSe and NiFe-LDH. The theoretical calculation showed that the generated electron transfer enable the electronic structure to be sufficiently modulated, which perfected the binding energy of the *OOH intermediates, issuing in a reduction of the reaction obstacle of the rate-determining procedure, and improved the OER activity consequently. This work proposes an effective and promising solution to fabricate non-precious metal-based heterostructure materials with excellent catalytic properties for energy storage and transduction.

Precipitation/dissolution equilibrium to achieve trace iron doping on the surface of β-Ni(OH)2 for electrocatalytic oxygen evolution

Nickel-iron bimetallic oxygen/hydroxide has become the benchmark for non-noble metal oxygen evolution reaction catalysts, but the challenge remains to maximize the density of Fe sites on the surface of nickel-based materials while improving the utilization rate of iron. Herein, Fe doped β-Ni(OH)2/NF with three-dimensional (3D) hybrid structure is synthesized by a facile two-step hydrothermal design. The doping of trace iron on the surface of β-Ni(OH)2 was achieved by precipitation/dissolution equilibrium while maintaining the order of the β-Ni(OH)2 matrix. The 3D hybrid structure provides more sites for iron incorporation on the surface/edge/corner of β-Ni(OH)2 host by precipitation/dissolution equilibrium doping mode. The addition of iron on the surface can expose more Fe-Ni-Fe sites, adjust the electronic structure of nickel sites, and optimize the adsorption/analytical energy of OER reaction intermediates. As expected, Fe2(0.1)-β-Ni(OH)2/NF demonstrates optimal OER catalytic activity, with only 300 mV overpotential at 100 mA cm−2 current density and a small Tafel slope up to 44.0 mV dec-1. Its morphology and OER performance present inconspicuous decay after 72 h of stable operation at 100 mA cm−2 current density. This paper provides a feasible path for the design and synthesis of trace doped bimetallic OER catalysts with high efficiency and stability.

Hollow CoP microspheres as superior bifunctional electrocatalysts for hydrogen evolution in a broad pH range and oxygen evolution reactions

Morphology regulation and ion doping are two common ways to improve catalytic performance. Herein, hollow CoP microspheres were synthesized via a facile template-free solvothermal approach with a following low-temperature phosphating process. The as-synthesized CoP hollow microspheres show preeminent electrocatalytic HER performance in a wide pH range (1.0 ​M KOH, 1.0 ​M PBS and 0.5 ​M ​H2SO4), and also deliver superior OER catalytic activity and low Tafel slope. Meanwhile, its catalytic activity could be maintained almost unchanged for at least 6 ​h in acidic solution, neutral solution and alkaline solution. These superior electrochemical properties will render the hollow CoP microsphere material as an attractive material for promising application in high-performance electrochemical water decomposition systems.

Application of Co/Co9S8@N, S doped porous carbon composites prepared by ball milling for zinc-air battery

• Metal sulfides were prepared by a unique strategy to achieve sulfidation and double doping with ammonium bisulfate. • The amount of ammonium bisulfate has a great effect on the synthesis of Co/Co 9 S 8 @N, S-PC. • Co/Co 9 S 8 @N, S-PC-N exhibits a unique porous morphology and optimized structure and composition. • Co/Co 9 S 8 @N, S-PC-N possesses outstanding exhibits the performance of double-effect oxygen catalysis. With the advantage of high electrocatalytic activity, cobalt sulfides has become an efficient electrocatalyst for oxygen evolution and oxygen reduction reaction (OER/ORR). Selecting an appropriate strategy to construct a optimal structure for cobalt sulfides to explore the potential of their application in zinc-air battery is one of the meaningful topics. Here we propose a facile strategy to synthesize Co/Co 9 S 8 @N, S doped porous carbon composite material with mesoporous structure by ball milling. The Co/Co 9 S 8 @N, S doped porous carbon composite material exhibits excellent dual function catalytic activity for OER and ORR. Also, the material exhibits excellent power density and cycle stability when applied to the electrode catalytic material of normal zinc-air battery. Among them, the optimal sample present better power density than Pt-Ru-C mixed catalyst used in the normal zinc-air battery, and the limit value is 202.5 mW cm -2 . Connecting two solid-state zinc-air batteries in series can meet the normal operation of 53 LED light-emitting diodes. This work can provide a powerful reference for the further development of cobalt sulfides in oxygen electrocatalysis and zinc-air battery.

Theoretical Study on the High HER/OER Electrocatalytic Activities of 2D GeSi, SnSi, and SnGe Monolayers and Further Improvement by Imposing Biaxial Strain or Doping Heteroatoms.

Under the DFT calculations, two-dimensional (2D) GeSi, SnSi, and SnGe monolayers, considered as the structural analogues of famous graphene, are confirmed to be dynamically, mechanically and thermodynamically stable, and all of them can also possess good conductivity. Furthermore, we systematically investigate their electrocatalytic activities in overall water splitting. The SnSi monolayer can show good HER catalytic activity, while the SnGe monolayer can display remarkable OER catalytic activity. In particular, the GeSi monolayer can even exhibit excellent bifunctional HER/OER electrocatalytic activities. In addition, applying the biaxial strain or doping heteroatoms (especially P atom) can be regarded as the effective strategies to further improve the HER activities of these three 2D monolayers. The doped GeSi and SnSi systems can usually exhibit higher HER activity than the doped SnGe systems. The correlative catalytic mechanisms are also analyzed. This work could open up a new avenue for the development of non-noble-metal-based HER/OER electrocatalysts.

Bifunctional electrocatalyst with CoN3 active sties dispersed on N-doped graphitic carbon nanosheets for ultrastable Zn-air batteries

Realizing large-scale production of low-cost bifunctional catalysts is pivotal to promoting the practical application of Zn-air batteries. Herein, we successfully constructed unique bifunctional CoN3 catalytic sites atomically dispersed on N-doped graphitic carbon nanosheets (CoSA/NCs), which enable Zn-air batteries with ultrahigh durability for over 6000 cycles (~ 2000 h). The 2D carbon construction and single-atom Co formation were achieved simultaneously in salt-assisted process employing CoCl2. CoCl2 serves as a recyclable template, a pore-making agent, and a catalyst for graphitization, which effectively enables the catalyst with abundant active sites catalyze ORR and OER. Our experimental and theoretical modeling results confirm that of CoN3 surpasses CoN4 in term of the ORR and OER catalytic activity. The Zn-air battery based on CoSA/NCs catalyst exhibits a high peak power density of 255 mW cm−2. With unparalleled catalytic performance and low production cost, this catalyst paves the way for the potential large-scale application of Zn-air batteries.

Ligand Stabilization Strategy Boosted Electrode Kinetics in Cyanide Metal Organic Framework for Electrocatalytic Oxygen Evolution Reaction

AbstractCyanide bridged frameworks are excellent pre‐catalysts towards oxygen evolution reaction. Control the hydrolysis product is crucial for design of highly active catalyst. Herein, we introduced pyrazine molecules pillared Hofmann‐type metal organic framework electrocatalysts. The in‐situ formed amorphous hydroxide provided high electrocatalytic activity and the interplanar pyrazine molecule offered structural stability towards alkaline environment, which effectively boosted the OER catalytic activity by offering more accessible active sites. The enhanced structural stability was justified by Raman spectroscopy. The overpotential, Tafel slope, and turn over frequency of the as‐synthesized Hofmann‐type MOF reached 306 mV, 15.6 mV dec−1 and 0.12 s−1, which is significantly better than that of Prussian blue analogue. This work justified the effectiveness of the ligand stabilization strategy in boosting the activity in OER catalysts.

Cover Feature: Hierarchical Fe Doped Co Oxide/Hydroxide Nanosheet Arrays as Highly Efficient Oxygen Evolution Catalysts Prepared by Hydrothermal Etching of FeCo Prussian Blue Analogue (Eur. J. Inorg. Chem. 17/2022)

The Cover Feature shows the oxygen evolution process catalyzed by a hierarchical FeCo oxide/hydroxide catalyst grown on Ni foam, which is prepared by a hydrothermal etching method with FeCo Prussian blue analogue as precursor. Spectroscopic and microscopic investigation demonstrated that the electronic structure of the surface was optimized by Fe doping, and more active sites were exposed with a self-standing 2D/2D hierarchical structure. The harmony of these two aspects contributes greatly to the outstanding OER catalytic activity. More information can be found in the Research Article by R. Xiang and co-workers.

Engineering eg Orbital Occupancy of Pt with Au Alloying Enables Reversible Li−O2 Batteries

AbstractConstructing well‐designed catalysts to accelerate OER catalytic activity and alleviate the charge overpotential is prevailing for achieving sophisticated Li−O2 batteries. Herein, we report a concept for engineering the eg occupancy of Pt with M alloying (M=Au, Ru) to tune the charge overpotentials for achieving high‐performance Li−O2 batteries. The X‐ray photoelectron spectroscopy results coupled with density functional theory (DFT) calculations reveal that the highly electronegative Au can capture more eg electrons from Pt, leading to less eg electrons of Pt in PtAu than that in PtRu. The lower eg occupancy of Pt atoms in PtAu alloys entails the upward shift of the Pt d band, which causes a strong binding strength towards the intermediates (LiO2), thereby decreasing the OER energy barrier. As a consequence, the Li−O2 battery with a PtAu cathode delivers a low charge overpotential of 0.36 V and superior cycle life of 220 cycles at a cutoff capacity of 1000 mAh g−1, which is among the best in the reported noble metal‐based cathodes.

Engineering eg Orbital Occupancy of Pt with Au Alloying Enables Reversible Li-O2 Batteries.

Constructing well-designed catalysts to accelerate OER catalytic activity and alleviate the charge overpotential is prevailing for achieving sophisticated Li-O2 batteries. Herein, we report a concept for engineering the eg occupancy of Pt with M alloying (M=Au, Ru) to tune the charge overpotentials for achieving high-performance Li-O2 batteries. The X-ray photoelectron spectroscopy results coupled with density functional theory (DFT) calculations reveal that the highly electronegative Au can capture more eg electrons from Pt, leading to less eg electrons of Pt in PtAu than that in PtRu. The lower eg occupancy of Pt atoms in PtAu alloys entails the upward shift of the Pt d band, which causes a strong binding strength towards the intermediates (LiO2 ), thereby decreasing the OER energy barrier. As a consequence, the Li-O2 battery with a PtAu cathode delivers a low charge overpotential of 0.36 V and superior cycle life of 220 cycles at a cutoff capacity of 1000 mAh g-1 , which is among the best in the reported noble metal-based cathodes.

Fe-ZIF-67-Derived FeCo/NC for Alkaline Water Splitting

Many results have demonstrated that non-noble metal–organic frameworks (MOFs) are good candidates as efficient catalyst templates for water splitting. In this syudy, Fe3+-containing ZIF-67 template is synthesized using the coprecipitation. We find that after pyrolysis Co2Fe4/NC exhibits excellent HER and OER catalytic activities with overpotential (the current density is 10 mA cm−2) values of 135 and 282 mV, respectively. In the overall water-splitting test, after running for 1000 cycles, the required voltage only increases by 24 mV from the onset of voltage 1.619 V. These superior results can be attributed to introduction of Fe3+ into the matrix and the increased active sites, which redistributes the d-band electron of Co atoms for better performance.

Pore architecture evolution and OER catalytic activity of hollow Co/Zn Zeolitic Imidazolate Frameworks

Tunable porosity through hollow features at nanoscale in metal organic frameworks (MOFs) can lead to enormous applications especially in catalysis. Hollow ZIF-67/ZIF-8 (core/shell) frameworks have been synthesized using solvothermal synthesis in methanol, wherein preformed ZIF-67 nanocrystals have been used as core. Using this method, hollow core/shell frameworks have been synthesized by excavation of ZIF-67 core and concurrent deposition of ZIF-8 shell for varying time. The crystal structure and chemical bonding of the frameworks have been characterized using X-ray diffraction, FTIR and Raman spectroscopy. Morphology of the hollow frameworks has been investigated using FE-SEM and EDX. Positron annihilation lifetime spectroscopy in combination with small angle X-ray scattering have been used to characterize the multiscale pore architecture (ultramicropores to mesopores) of these hollow frameworks. The sodalite topology and associated pore architecture of ZIFs are retained during the synthesis of hollow framework, however the excavation of core leads to enhancement in mesopores. Hollow frameworks have been tested for their performance towards oxygen evolution reaction. The hollow frameworks show improvement in the catalytic activity as compared to pure ZIF-67 nanocrystals. It is proposed that in order to further improve their catalytic performance, post-synthesis modifications for enhancement in stability of pore network of shell and loading of active species are required. • Hollow ZIF-67/ZIF-8 (core/shell) frameworks have been synthesized. • Mesoporosity of hollow frameworks varies with excavation time. • Pore architecture and topology of shell is retained during excavation. • PALS in combination with SAXS is useful for ultramicropores to mesopores characterization of MOFs. • OER catalytic activity of hollow framework is superior as compared to pure ZIF-67.

Tuning the Co3+/Co2+ ratios of the CoSx/CNT nanocomposites for efficient oxygen evolution reaction (OER)

Considering the price and catalytic performance, cobalt sulfide catalysts have good application potential in electrochemical water splitting. Controlling the Co3+/Co2+ ratios of cobalt sulfide can tune its electronic structure and further optimize its catalytic performance. Herein, the CoSx/CNT (carbon nanotube) nanocomposites with various Co3+/Co2+ ratios were designed and prepared by different sulfurization strategies. The CoSx/CNT-700 with the highest Co3+/Co2+ ratio exhibits the most excellent OER electrocatalytic activity in 1 M KOH, including a low overpotential of 320 mV at 10 mA cm−2, and a small Tafel slope of 71.9 mV dec-1. The experimental results indicate that tuning the Co3+/Co2+ ratios can improve the OER catalytic activity.

Ab Initio Exploration of Energetically and Kinetically Favorable ORR Activity on a 1T-ZrO2 Monolayer for a Nonaqueous Lithium-Oxygen Battery.

Herein, we explore the potential applications of the experimentally synthesized ZrO2 monolayer as the cathode catalyst for nonaqueous lithium-oxygen batteries. First, we show that a new peroxide-like adsorption geometry is the most stable configuration for LiO2, which is distinct from the previously known O-Li-O triangular geometry. The proposed most stable adsorption configuration is because the Zr atoms in the substrate play a critical role in stabilizing the LiO2 cluster. Second, our ab initio calculations indicate that both the ORR and OER catalytic activities are most likely to adopt the four-electron mechanism with a considerably low overpotential of only 0.44 and 0.76 V, respectively. Finally, we show that the adsorption energy of Li2O2 is a good descriptor for both ORR and OER catalytic activities, and weak Li2O2 adsorption behavior is positively related to low overpotentials and satisfactory catalytic performance.

Facile synthesis MnCo2O4.5@C nanospheres modifying PbO2 energy-saving electrode for zinc electrowinning

The oxygen evolution reaction kinetics in industrial zinc electrowinning is sluggish, resulting in low electrocatalytic activity and substantial energy expenditure (about one-third of energy was wasted due to the strong polarization effect). Herein, the paper described a core-shell structured MnCo2O4.5@C modified PbO2 electrode through the pyrolysis and co-electrodeposition as a promising candidate for zinc electrowinning. As a result, the obtained Pb-0.2%Ag/α-PbO2/β-PbO2-MnCo2O4.5@C composite electrode showed a sandwich-like structure, where Pb-0.2%Ag as a core, α-PbO2 as a mid-layer, and β-PbO2-MnCo2O4.5@C served as an electrocatalytic layer. It also possessed improved OER catalytic activity, only required 680 mV to achieve a current density of 50 mA cm−2 and a Tafel slope of 216.04 mV dec−1 in an acidic solution containing 50 g L−1 Zn2+ and 150 g L−1 H2SO4. The current efficiency increased by 0.7% and the cell voltage reduced by 360 mV as compared to a conventional Pb-0.76%Ag alloy electrode, leading to a remarkable energy-consumption reduction of 283.5 kW h for producing per ton metallic zinc. Furthermore, Pb-0.2%Ag/α-PbO2/β-PbO2-MnCo2O4.5@C exhibited a prolonged service life, which worked about 44 h under an ultra-high current density of 2 A cm−2. Hence, this paper provides the strategy to design and construct non-precious, high-performance catalyst for electrolysis and other applications.

Nanostructured IrO x supported on N-doped TiO2 as an efficient electrocatalyst towards acidic oxygen evolution reaction.

Reducing the Ir consumption without compromising the catalytic performance for the oxygen evolution reaction (OER) is highly paramount to promote the extensive development of the environmentally-friendly solid polymer electrolyte water electrolysis (SPEWE) system. Herein, TiO2 is doped with N through facile NH3 gas treatment and innovatively employed to support IrO x nanoparticles towards acidic OER. N-doping action not only dramatically boosts the electrical conductivity and dispersing/anchoring effects of TiO2, but also effectively improves the electron-transfer procedure. As a result, the IrO x /N-TiO2 electrocatalyst exhibits prominent catalyst utilization, catalytic activity and stability. Specifically, the overpotential required to deliver 10 mA cm-2 is only 270 mV, and the mass activity climbs to 278.7 A gIr -1 @ 1.55 VRHE. Moreover, the single cell voltage is only 1.761 V @ 2.0 A cm-2 when adopting IrO x /N-TiO2 as the anode catalyst, which is 44 mV lower than that of the commercial IrO2 counterpart.