Stable Bifunctional Electrocatalysts Research Articles

Free-standing FeNiCuCoBMo high-entropy alloy bifunctional electrocatalysts for efficient pH-universal water electrolysis

Utilizing the synergistic effects of multi-components has been proven to be a feasible approach to enhance water splitting electrocatalytic activity, since developing efficient and stable bifunctional electrocatalysts within a wide pH range remains a significant challenge. Herein, we report a FeNiCuCoBMo high-entropy alloy (HEA) prepared by dealloying, showing outstanding bifunctional electrocatalytic performance for HER and OER in a pH-universal electrolyte. After dealloying for 7 h, the HER and OER overpotentials of the HEA strips in 1.0 M KOH decreased by 22 mV and 25 mV, respectively.Impressively, the free-standing strips with the optimal compositions achieve low HER (82 mV in acid and 101 mV in alkali at 10 mA·cm−2) and OER (311 mV in acid and 245 mV in alkali at 10 mA·cm−2) overpotentials. In a full hydrolysis experiment, a current of 10 mA·cm−2 can run for 100 h with only 1.58 V, which is attributed to the ample exposure of highly active sites resulting from the synergistic effect of each element. Theoretical calculations further support these findings, showing that the electronegativity differences of the metallic elements in FeNiCuCoBMo result in abnormal activity at specific locations (Fe and Mo).Additionally, charge rearrangement and enhanced electronic conduction at the interface reduce the activation energy barrier, thereby improving the performance of the electrocatalysts.

Spider silk inspired ultrafine carbon nanotubes-crosslinked porous carbon fibers for Zn-air batteries

There is a critical need for the development of low-cost, highly efficient, and stable bifunctional oxygen electrocatalysts for the advancement of Zn-air battery (ZAB). This study presents an Fe-, Ni-, and N-co-doped porous carbon material (FeNiN-CF-15) synthesized through the pyrolysis of a mixture combining the melamine and electrospun fibers. This material comprises carbon fiber substrates and spider silk-like ultrafine carbon nanotubes (CNTs) catalytically grown from FeNi alloys. With a high N doping level (12.9 at%), large specific surface area (385.18 m2 g−1), and conductive carbon network composed of CNTs, the new electrocatalyst exhibits outstanding bifunctional oxygen electrocatalytic performances. Specifically, it achieves a half-wave potential of 0.853 V for oxygen reduction reaction (ORR) and 1.571 V for oxygen evolution reaction (OER) at 10 mA cm−2. The exceptional ORR/OER electrocatalytic activity enables the FeNiN-CF-15-based liquid ZAB to deliver a high initial energy efficiency of 62.12 %, narrow charging/discharging voltage gap of 0.742 V, and robust cycling stability within 960 cycles for 320 h at 5 mA cm−2. Additionally, the reported electrocatalyst is proven competent for use in a flexible ZAB.

Low Rh doping accelerated HER/OER bifunctional catalytic activities of nanoflower-like Ni-Co sulfide for greatly boosting overall water splitting

Facile synthesis of high-efficiency and stable bifunctional electrocatalyst is essential for producing clean hydrogen in energy storage systems. Herein, low Rh-doped flower-like Ni3S2/Co3S4 heterostructures were facilely prepared on porous nickel foam (labeled Rh-Ni3S2/Co3S4/NF) by a hydrothermal method. The correlation of the precursors types with the morphological structures and catalytic properties were rigorously investigated for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in the control groups. The low Rh doping within the catalyst played important role in boosting the catalytic characteristics. The resulting catalyst showed the smaller overpotentials of 197 and 78 mV to drive a current density of 10 mA cm−2 for the OER and HER in alkaline electrolyte, respectively. And the potential only required 1.71 V to drive a current density of 100 mA cm-2 in a water splitting device. It reflects excellent overall water splitting of the home-made Rh-Ni3S2/Co3S4/NF. This strategy shed some constructive light for preparing transition metal sulfide-based electrocatalysts in water splitting devices.

Constructing a Self-Supported Bifunctional Multiphase Heterostructure for Electrocatalytic Overall Water Splitting.

Developing well-performing and stable bifunctional electrocatalysts is of great importance for efficient green hydrogen production through water electrolysis. Herein, a three-dimensional self-supported CoMoS3.13/FeS2/Co3S4 on carbon paper (FeCoMoS/CP) heterostructure with interconnected nanosheets for overall water splitting was fabricated by a facile hydrothermal method followed by vulcanization treatment. The FeCoMoS/CP heterostructure with high structural integrity and more accessible active sites can effectively optimize the electronic structure through component regulation to achieve enhanced catalytic activity. Significantly, the FeCoMoS/CP required overpotentials of 257 mV at 50 mA cm-2 for OER and 280 mV at 20 mA cm-2 for HER. Importantly, the assembled FeCoMoS/CP||FeCoMoS/CP alkaline electrolyzer achieved a superior cell voltage of 1.48 V at 10 mA cm-2 with superb long-term stability, which implies a remarkable electrocatalytic performance of the FeCoMoS/CP heterostructure for overall water splitting. This work provides an applicable route for synthesizing high-performance bifunctional catalysts toward water electrolysis.

Surfactant-free CuPd nano-alloy for N2H4 oxidation-assisted H2 evolution and H2O2 detection

The utilization of hydrazine oxidation reaction (HzOR) with a lower thermodynamic oxidation potential has been regarded as an efficient strategy for H2 generation through electrolysis. However, a highly efficient and stable bifunctional electrocatalyst for overall hydrazine (N2H4) splitting was scarce. This work verified promising CuPd nano-alloy as a bifunctional electrocatalys for energy-efficient electrolytic hydrogen production, with hydrazine assistance. It is demonstrated that the CuPd nano-alloy exhibited enhanced electrocatalytic activity for both cathodic and anodic reactions compared to pure Cu and Pd nanocrystals, benefiting from its favorable electronic structure. Under 1.0 M KOH electrolyte with 0.1 M N2H4, the surfactant-free CuPd nano-alloy only required a potential of 0.648 V to achieve the N2H4 splitting (OHzS). The surfactant-free surface maximized exposed active sites, which facilitated the adsorption and desorption of reactants, resulting in enhanced electrocatalytic activity. And working potential for HzOR by surfactant-free CuPd was only 50.4 % compared to the CuPd nano-alloy with surfactant. This work provided an efficient electrocatalyst for OHzS. The enhanced electro-catalytic performances resulting from the electronic structure of alloy and the surfactant-free interface effect have been thoroughly discussed and verified, which would be invaluable for the design of efficient electrocatalysts for H2 production.

Mn incorporated RuO2 nanocrystals as an efficient and stable bifunctional electrocatalyst for oxygen evolution reaction and hydrogen evolution reaction in acid and alkaline

The development of efficient and stable bifunctional overall water-splitting is a crucial goal for clean and renewable energy, which is a challenging task. Herein, we report an Mn-incorporated RuO2 (Mn-RuO2) catalyst for highly efficient electrocatalytic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in acid and alkaline media. Benefiting from a more electrochemical active area with the incorporation of Mn, the Mn-RuO2 required an overpotential of 200 mV to attain a current density of 10 mA/cm2 for OER in acid. DFT result indicates that the doping of Mn into RuO2 can enhance the OER activity. An acidic overall water-splitting electrolyzer with good stability constructed by bifunctional Mn-RuO2 only requires a cell voltage of 1.50 V to afford 10 mA/cm2 and can operate stably for 50 h at 50 mA/cm2, which is better than the state-of-the-art Ru-based catalyst. Additionally, the Mn-RuO2 exhibits excellent HER and OER activity in alkaline media, and it shows superior activity and durability for overall water-splitting, only needing a cell voltage of 1.49 V to attain 10 mA/cm2. The present work provides an efficient approach to designing and constructing efficient Ru-based electrocatalysts for overall water-splitting.

One-step electrodeposition of bifunctional MnCoPi electrocatalysts with wrinkled globular-flowers-like structure for highly efficient electrocatalytic water splitting

The development and exploration of electrocatalysts with the high reactive and abundant availability is still extremely crucial in electrocatalytic overall water splitting. Herein, a novel globular-flowers-like MnO2/Co3(PO4)2 (denoted as MnCoPi) electrocatalyst on nickel foam was successfully prepared through a simple one-step electrodeposition method. The MnCoPi electrocatalyst simultaneously delivers remarkable electrocatalytic activities for hydrogen evolution reaction (HER) with overpotentials (η10) reaching 102 mV and oxygen evolution reaction (OER) with overpotentials (η10) up to 225 mV in 1 M KOH solution. Furthermore, the assembled electrolyzer cell utilizing MnCoPi as the cathode and anode only requires a low voltage of 1.55 V to achieve a current density of 10 mA cm−2. Moreover, the developed MnCoPi electrocatalyst shows excellent stability during continuous operation for 48 h in OER, HER and overall water splitting process. Compared with the pristine MnO2, the significant electrocatalytic properties of MnCoPi can mainly be attributed to the improved physicochemical properties such as distinctive globular-flowers-like morphology, huge specific surface areas and abundant porosity structure, low electrochemical resistance, especially for the formed heterojunction between MnO2 and Co3(PO4)2, which can provide abundant reactive sites and accelerated electron transfer, etc. Consequently, this work provides a new avenue for the development of efficient and stable bifunctional electrocatalysts for overall water splitting.

Synthesis of Ni-doped 1T/2H MoS2 nanoparticles as an efficient and stable bifunctional electrocatalyst for overall water-splitting

In advancing hydrogen fuel production through water-splitting, we focus on the optimisation of 1T/2H phases of MoS2 nanoparticles to enrich the overall water-splitting performance which has garnered significant interest. We propose a straightforward hydrothermal method to develop a 1T/2H MoS2 catalyst by introducing Ni. Morphological and chemical investigations evidenced the generation of the metal/semiconductor MoS2 nanoparticles. Further, the electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have been demonstrated, and the optimised 1 m mol nickel-doped MoS2 catalyst (MSN-1) exhibits remarkable performance in both HER and OER, with a low overpotential of 117 and 250 mV respectively at a current density of 10 mA cm−2, and superior stability in alkaline medium (about 20 h). Additionally, it exhibits promising bifunctional activity with an overpotential of approximately 1.36 V at a current density of 10 mA cm−2, maintaining stability for 20 h in a 1.0 M KOH medium. These outcomes emphasise that MSN-1 has the potential as a practical bifunctional electrocatalyst with significant applications on the horizon.

General and Facile Synthesis of Co/CoO Nanoparticals Supported by Nitrogen-Doped Graphenic Networks as Efficient Oxygen Electrocatalyst for Zn-Air Batteries.

Reasonable design of low-cost, high-efficiency and stable bifunctional oxygen electrocatalysts is of great significance to improve the reaction efficiency of Zn-air batteries, which is still a huge challenge. Here, we report a highly efficient bifunctional oxygen electrocatalyst with three-dimensional (3D) N-doped graphene network-supported cobalt and cobalt oxide nanoparticles (Co/CoO-NG), which can be in situ synthesized by inducing metal ions on metal plates via graphene oxide as an inducer. This 3D network structure and open active center show excellent bifunctional oxygen electrocatalytic activity under alkaline conditions, and can be used as an air electrode in rechargeable Zn-air batteries, with significantly better power density (244.28 mW cm-2) and stability (over 340 h) than commercial Pt/C+RuO2 mixtures. This work is conducive to advancing the practical application of graphene-based materials as air electrodes for rechargeable zinc-air batteries.

Synergistic Ru/RuO2 heterojunctions stabilized by carbon coating as efficient and stable bifunctional electrocatalysts for acidic overall water splitting

Synergistic Ru/RuO2 heterojunctions stabilized by carbon coating as efficient and stable bifunctional electrocatalysts for acidic overall water splitting

Electron Manipulation and Surface Reconstruction of Bimetallic Iron-Nickel Phosphide Nanotubes for Enhanced Alkaline Water Electrolysis.

Developing high-efficiency and stable bifunctional electrocatalysts for water splitting remains a great challenge. Herein, NiMoO4 nanowires as sacrificial templates to synthesize Mo-doped NiFe Prussian blue analogs are employed, which can be easily phosphorized to Mo-doped Fe2xNi2(1-x)P nanotubes (Mo-FeNiP NTs). This synthesis method enables the controlled etching of NiMoO4 nanowires that results in a unique hollow nanotube architecture. As a bifunctional catalyst, the Mo-FeNiP NTs present lower overpotential and Tafel slope of 151.3 (232.6) mV at 100 mA cm-2 and 76.2 (64.7) mV dec-1 for HER (OER), respectively. Additionally, it only requires an ultralow cell voltage of 1.47 V to achieve 10 mA cm-2 for overall water splitting and can steadily operate for 200 h at 100 mA cm-2. First-principles calculations demonstrate that Mo doping can effectively adjust the electron redistribution of the Ni hollow sites to optimize the hydrogen adsorption-free energy for HER. Besides, in situ Raman characterization reveals the dissolving of doped Mo can promote a rapid surface reconstruction on Mo-FeNiP NTs to dynamically stable (Fe)Ni-oxyhydroxide layers, serving as the actual active species for OER. The work proposes a rational approach addressed by electron manipulation and surface reconstruction of bimetallic phosphides to regulate both the HER and OER activity.

Value‐Added Cascade Synthesis Mediated by Paired‐Electrolysis Using an Ultrathin Microenvironment‐Inbuilt Metalized Covalent Organic Framework Heterojunction

AbstractEnergy‐saving and value‐added management in advanced catalysis is highly desirable but is challenged by the limitations of multifunctional catalysts and catalytic modules. Herein, an azo‐linked phthalocyanine‐porphyrin covalent organic framework (COF) with the ultrathin layered nanostructure grown on carbon nanotubes (NiPc‐azo‐H2Pp@CNTs) has been designed and synthesized, which can serve as a highly active and stable bifunctional heterojunction electrocatalyst for selective paired‐electrosynthesis through coupling anodic iodide oxidation reaction and cathodic CO2 conversion. Particularly, the inbuilt local microenvironment conferred by the dihydroporphyrin moieties in COF can act as a proton reservoir to promote the proton relay at the heterojunction interface during the electrocatalytic process. Moreover, through the cascade construction of dual electrocatalytic/organocatalytic modules, the cathode‐generated CO can be further converted to dimethyl carbonate with a yield of 6.21 mmol L−1 h−1, while the anode‐produced iodine can be derived into iodoform on the hundred‐milligram scale. It is worth noting that the value‐added cascade synthesis mediated by paired‐electrolysis using the distinctive and high‐powered electrocatalysts will help advance the sustainable development of industrial intelligent manufacturing.

Controllable La Deficiency Engineering within Perovskite Oxides for Enhanced Overall Water Splitting.

Recently, perovskite (ABO3) nanomaterials have been widely explored as a class of versatile electrocatalysts for oxygen evolution reactions (OER) due to their remarkable compositional flexibility and structural tunability, but their poor electrical conductivity hinders hydrogen evolution reaction (HER) activity and further limits the large-scale application of perovskite oxide in overall water splitting (OWS). In this study, hollow-nanotube-structure LaxCo0.4Fe0.6O3-δ (x = 1.0, 0.9, and 0.8) perovskites with superior HER/OER activity were synthesized on nickel-iron alloy foam (denoted LaxCoFe/NFF) using hydrothermal with a subsequent calcination strategy. Among them, La0.9CoFe/NFF not only exhibited extraordinary HER electrocatalytic performance (160.5 mV@10 mA cm-2 and 241.0 mV@100 mA cm-2) and stability (20 h@10 mA cm-2), but also displayed significant OER electrocatalytic activity (234.7 mV@10 mA cm-2 and 296.1 mV@100 mA cm-2) and durability (20 h@10 mA cm-2), outperforming many recently reported HER/OER perovskite catalysts. The increase in oxygen vacancies caused by the introduction of La deficiency leads to the expansion of the lattice, which greatly accelerates the HER/OER process of La0.9CoFe/NFF. Additionally, the naturally porous skeleton can prevent catalysts from aggregating as well as delay the corrosion and dissolution of catalysts in the electrolyte under high applied potentials. Furthermore, the assembled two-electrode configuration, utilizing La0.9CoFe/NFF (cathode and anode) electrodes, only requires a low cell voltage of 1.573 V at 10 mA cm-2 for robust alkaline OWS, accompanied by remarkable durability over 20 h. This work provides inspiration for the design and preparation of high-performance and stable bifunctional perovskite electrocatalysts for OWS.

Three-dimensional cage based on porous Ni–Co–Cu phosphide as efficient and stable bifunctional electrocatalysts for overall water splitting

The development of cheap and high-performance dual electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an electrolyte is of great importance. Tuning the electronic structure through heteroatom doping and increasing the catalytic sites through designing the morphology of nanostructures are the most popular approaches to enhance electrocatalytic performance. In recent years, with the development of nanotechnology and interface engineering, significant progress has been made in this field, but it is still challenging. Here three-dimensional porous NiCoCu–P cage were synthesized using a quick and easy method with the help of 26-face Cu2O as a sacrificial template, then it was phosphidated by a facile phosphidation heat treatment in N2 atmosphere and then for the electrochemical evaluations, the glassy carbon electrode surface (GCE) surface was modified with it. Taking advantage of these strategies, NiCoCu–P cage offer large surface area, fast electron/mass transfer and open channels for efficient gas release, which show improved electrochemical performance in alkaline environment and achieved an overpotential of −210 mV at 10 mA cm−2 for HER and 240 mV at 50 mA cm−2 for OER. Also, an overall water splitting device is assembled by two symmetric NiCoCu–P cage/carbon cloth as cathode and anode, that can provide a current density of 100 mA cm−2 at a cell voltage of less than 1.6 V.

Nickel‐Foam‐ and Carbon‐Nanotubes‐Fiber‐Supported Bismuth Oxide/Nickel Oxide Composite; Highly Active and Stable Bifunctional Electrocatalysts for Water Splitting in Neutral and Alkaline Media

To increase the effectiveness of both the cathodic hydrogen evolution reaction (HER) and the anodic oxygen evolution reaction (OER), significant efforts are made to produce bifunctional water‐splitting electrocatalysts. In this study, bismuth oxide/nickel oxide (Bi2O3/NiO)‐based composite is supported over the nickel foam (Bi2O3/NiO‐NF) and carbon nanotube fiber (Bi2O3/NiO‐CNTF) to develop two different electrode systems for water‐splitting studies. For OER, Bi2O3/NiO‐NF and Bi2O3/NiO‐CNTF require overpotential of 401 and 369 mV, respectively, to achieve the current density of 50 mA cm−2 in alkaline media, while the current density of 50 mA cm−2 is achieved at overpotential of 398 and 304 mV, respectively, in neutral media. For HER, Bi2O3/NiO‐NF and Bi2O3/NiO‐CNTF achieve the current density of 50 mA cm−2 at overpotential of 301 and 268 mV, respectively, in neutral media. For overall water splitting in neutral media, Bi2O3/NiO‐CNTF achieves the current density of 50 mA cm−2 at cell voltage of 1.654 V. The promising performance of synthesized electrocatalysts reveals that the mixed metal oxides (p‐block and d‐block elements)‐based electrocatalysts can be potential candidates for practical water splitting in basic (1 M KOH) as well as neutral media (1 M phosphate‐buffered saline).

Bifunctional Substrates: In‐situ Ni, Fe co‐doped Cobalt Carbonate Hydroxides for Overall Water Splitting

AbstractDeveloping highly efficient and stable electrocatalysts with large current densities for hydrogen and oxygen evolution is still challenging. Herein, Ni and Fe co‐doped cobalt carbonate hydroxide catalysts were designed in situ on the three‐dimensional porous NiFe foam through a facile one‐step hydrothermal strategy. Inductively coupled plasma atomic emission spectrum, transmission electron microscopy‐element mapping, X‐ray photoelectron spectroscopy, and DFT calculations demonstrate that the three‐dimensional NiFe foam substrate not only serves as the porous substrate, which enhances the exposed number of active sites, but also enhances the intrinsic activities of single active sites via introducing Ni and Fe dopants in the cobalt carbonate hydroxide catalyst during the hydrothermal process. The obtained hybrid electrocatalyst can be employed as a highly efficient and stable bifunctional electrocatalyst for the oxygen and hydrogen evolution reactions, with overpotentials of 340 mV and 371 mV at 1000 mA cm−2, respectively. In addition, tests in an alkaline electrolyzer revealed that the current density could reach 1000 mA cm−2 at a voltage of 2 V and maintain stable operation for 100 h.

Hydrogel derived N, P co-doped porous defective carbon framework anchored with Co2P nanoparticles as robust electrocatalysts for Zn-air battery

Recently, it is critical but a challenge to exploit economical, high active and stable bifunctional oxygen electrocatalysts for advanced rechargeable Zn-air batteries (ZABs). Herein, a robust ORR/OER electrocatalyst (Co2P/H-NPC) was prepared using Co2P nanoparticles (NPs) anchored on a N,P-doped three-dimensional (3D) hierarchically porous carbon framework with rich defects through carbonizing a hydrogel, involving starch, polyinosinic acid, cobalt(II) acetate and NH4Cl. Co2P NPs and the dual doping of heteroatoms (N and P), as well as the hierarchically porous feature, synergistically endow Co2P/H-NPC with an excellent ORR and OER activities, in terms of positive half-wave potential (0.83 V) and low overpotential (390 mV) at a current density of 10 mA cm−2, respectively. Additionally, the assembled ZAB based on Co2P/H-NPC delivers a peak power density of 120 mW cm−2, and a wonderful discharge-charge cycling stability, indicating good potential for further application in the fields of energy storage and conversion devices.

Modulating electronic structure of nickel diselenide by vanadium doping toward highly efficient and stable bifunctional electrocatalysts for overall water splitting

Designing low-cost and high-efficiency bifunctional electrocatalysts is one of the challenges in the clean production of hydrogen energy in electrochemical water splitting. Transition metal selenides (TMSes) have been widely studied because of their low price, intrinsic metal properties, and high catalytic activity. In addition, the synergistic effect between bimetallic selenides exhibits better performance than monometallic selenides in the electrocatalytic process. Herein, we synthesized V-doped NiSe2 nanowire arrays on pretreated nickel foam by a convenient two-step hydrothermal synthesis method. In the alkaline electrolyte, V-NiSe2/NF exhibited excellent OER catalytic activity (293.6 mV@50 mA cm–2). In addition, the introduction of heteroatom V induces stronger electronic interactions between the structural atoms of the catalyst, altering the electronic structure and causing V-NiSe2/NF to demonstrate excellent OER performance. In the long-term OER test, V-NiSe2/NF was converted into NiOOH and SeOx2–, which may be the “real” active species during catalytic reactions, and we also successfully captured the formation of intermediate NiOOH and selenite as active centers in the OER process through in-situ Raman. The theoretical calculation shows that the electron transfer modulates the electron structure, changes the adsorption-desorption energy of the reaction intermediates, reduces the potential barrier of the rate-limiting step, and improves the OER activity. The V doping engineering strategy and the unique nanowire array structure make TMSes exhibit excellent OER performance. This study provides a new idea for the design of TMSe catalysts with excellent electrocatalytic performance.

Enhancing the efficiency and stability of electrocatalysts for water splitting: NiCo-LDH nanosheet arrays at high current density

The development of low-cost, efficient, and stable bifunctional electrocatalysts is very important for the development of renewable energy.

Designing bifunctional perovskite catalysts for the oxygen reduction and evolution reactions.

The development of unified regenerative fuel cells (URFCs) necessitates an active and stable bifunctional oxygen electrocatalyst. The unique challenge of possessing high activity for both the oxygen reduction (ORR) and oxygen evolution (OER) reactions, while maintaining stability over a wide potential window impedes the design of bifunctional oxygen electrocatalysts. Herein, two design strategies are explored to optimize their performance. The first incorporates active sites for the ORR and OER, Mn and Co, into a single perovskite structure, which is achieved with the perovskites Ba0.5Sr0.5Co0.8Mn0.2O3-δ (BSCM) and La0.5Ba0.25Sr0.25Co0.5Mn0.5O3-δ (LBSCM). The second combines an active ORR perovskite catalyst (La0.4Sr0.6MnO3-δ (LSM)) with an OER active perovskite catalyst (Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF)) in a physical mixed composite (BSCF/LSM). The success of the two strategies is investigated by measuring the catalysts' catalytic performance and response to alternating reducing and oxidizing potentials to mimic the dynamic conditions experienced during the operation of URFCs. Additionally, the continuous, potentiodynamic change in Mn, Co, and Fe oxidation states during the ORR and OER is elucidated with operando X-ray absorption spectroscopy (XAS) measurements, revealing key insights into the nature of the active sites. The results reveal important catalyst physiochemical properties and provide a guide for future research and design principles for bifunctional oxygen electrocatalysts.