CNT-interconnected iron-doped NiP2/Ni2P heterostructural nanoflowers as high-efficiency electrocatalyst for oxygen evolution reaction

Oxygen evolution reaction (OER) plays a decisive role in electrolytic water splitting. However, it is still challengeable to develop low-cost and efficient OER electrocatalysts. Herein, we present a combination strategy via heteroatom doping, hetero-interface engineering and introducing conductive skeleton to synthesize a hybrid OER catalyst of CNT-interconnected iron-doped NiP₂/Ni₂P (Fe-(NiP₂/Ni₂P)@CNT) heterostructural nanoflowers by a simple hydrothermal reaction and subsequent phosphorization process. The optimized Fe-(NiP₂/Ni₂P)@CNT catalyst delivers an ultralow Tafel slope of 46.1 mV dec^?1 and overpotential of 254 mV to obtain 10 mA cm^?2, which are even better than those of commercial OER catalyst RuO₂. The excellent OER performance is mainly attributed to its unique nanoarchitecture and the synergistic effects: the nanoflowers constructed by a 2D-like nanosheets guarantee large specific area and abundant active sites; the highly conductive CNT skeleton and the electronic modulation by the heterostructural NiP₂/Ni₂P interface and the hetero-atom doping can improve the catalytic activity; porous nanostructure benefits electrolyte penetration and gas release; most importantly, the rough surface and rich defects caused by phosphorization process can further enhance the OER performance. This work provides a deep insight to boost catalytic performance by heteroatom doping and interface engineering for water splitting.     

Facile synthesis of bimetallic Ni–Fe phosphide as robust electrocatalyst for oxygen evolution reaction in alkaline media

Bimetallic Ni–Fe phosphide electrocatalysts were in-situ synthesized through direct phosphorization of metal salts on carbon cloth (CC). The Fe dopant remarkably enhances the OER performance of Ni₂P in alkaline medium through the electronic structure modulation of Ni. The (Fe_0.5Ni_0.5)₂P/CC electrode, composed of uniform films coated on carbon fibers, delivers a low overpotential of 260 mV with a small Tafel slope of 45 mV·dec⁻¹ at the current density of 100 mA cm⁻², outperforming most reported non-noble electrocatalysts and commercial RuO₂ electrocatalyst. The (Fe_0.5Ni_0.5)₂P/CC also displays superior electrochemical stability at high current density. An appropriate Fe dopant level facilitates the in-situ transformation of Ni–Fe phosphides into active NiFeOOH during alkaline OER. This work simplifies the synthesis procedure of metal phosphides.     

Top-down preparation of Ni–Pd–P@graphitic carbon core-shell nanostructure as a non-Pt catalyst for enhanced electrocatalytic reactions

Electrochemical reactions such as the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and methanol oxidation reaction (MOR) are essential for energy conversion applications such as water electrolysis and fuel cells. Furthermore, Pt or Ir-related materials have been extensively utilized as electrocatalysts for the OER, ORR, and MOR. To reduce the utilization of precious metals, innovative catalyst structures should be proposed. Herein, we report a bi-metallic phosphide (Ni₂P and PdP₂) structure surrounded by graphitic carbon (Ni–Pd–P/C) with an enhanced electrochemical activity as compared to conventional electrocatalysts. Despite the low Pd content of 3 at%, Ni–Pd–P/C exhibits a low overpotential of 330 mV at 10 mA cm^?2 in the OER, high specific activity (2.82 mA cm^?2 at 0.8 V) for the ORR, and a high current density of 1.101 A mg^?1 for the MOR. The superior electrochemical performance of Ni–Pd–P/C may be attributed to the synergistic effect of the bi-metallic phosphide structure and core-shell structure formed by graphitic carbon.     

Core-shell Ni3Fe-based nanocomposites for the oxygen evolution reaction

To deal with energy and environmental issues, it is necessary to exploit efficient and stable electrocatalysts for the generation of clean hydrogen. Herein, we describe the synthesis of bimetallic Fe/Ni alloy encapsulated by amorphous carbon shells via a facile annealing strategy for electrocatalytic oxygen evolution reaction (OER). The ferric nickel tartrate annealed at 800 °C (Ni₃Fe₁O_x@C-800) exhibits a low OER overpotential of 264 mV at 10 mA cm^?2 and good stability in alkaline media. Compared with monometallic counterpart, bimetallic Ni₃Fe-based nanocomposites show lower OER barrier (ca. 324 kJ mol^?1) due to a cooperation mechanism between Ni and Fe sites in promoting electrocatalytic water oxidation. Compared with those annealed at other temperatures, the enhanced OER performance of Ni₃Fe₁O_x@C-800 can be ascribed to the large electrochemical surface area for exposing more active sites, smaller charge transfer, and better intrinsic activity of Ni₃Fe-based sites.     

Porous NiFe alloys synthesized via freeze casting as bifunctional electrocatalysts for oxygen and hydrogen evolution reaction

Binder-free NiFe-based electrocatalyst with aligned pore channels has been prepared by freeze casting and served as a bifunctional catalytic electrode for oxygen and hydrogen evolution reaction (OER and HER). The synergistic effects between Ni and Fe result in the high electrocatalytic performance of porous NiFe electrodes. In 1.0 M KOH, porous Ni₇Fe₃ attains 100 mA cm⁻² at an overpotential of 388 mV with a Tafel slope of 35.8 mV dec⁻¹ for OER, and porous Ni₉Fe₁ exhibits a low overpotential of 347 mV at 100 mA cm⁻² with a Tafel slope of 121.0 mV dec⁻¹ for HER. The Ni₉Fe₁//Ni₉Fe₁ requires a low cell voltage of 1.69 V to deliver 10 mA cm⁻² current density for overall water splitting. The excellent durability at a high current density of porous NiFe electrodes has been confirmed during OER, HER and overall water splitting. The fine electrocatalytic performances of the porous NiFe-based electrodes owing to the three-dimensionally well-connected scaffolds, aligned pore channels, and bimetallic synergy, offering excellent charge/ion transfer efficiency and sizeable active surface area. Freeze casting can be applied to design and synthesize various three-dimensionally porous non-precious metal-based electrocatalysts with controllable multiphase for energy conversion and storage.     

Tuning the d-band center enables nickel-iron phosphide nanoprisms as efficient electrocatalyst towards oxygen evolution

Highly active and low-cost catalytic electrodes for oxygen evolution reaction (OER) are always crucial for obtaining clean hydrogen energy via large-scale electrolytic water splitting. Herein, endowing the nickel-iron phosphide (NiFeP) nanoprisms with the tunable electronic structures have been carried out by tailoring the energy level of d-band in our study. The bimetallic synergistic effect efficiently accelerates the formation and cleavage rates of MO bonding, enabling the greatly improved OER catalytic performance after doping Fe into Ni₂P. The large surface area benefiting from the porous architecture also facilitates more contact between electrocatalyst and alkaline electrolytes, resulting in an advanced OER activity. Therefore, NiFeP can drive the OER process with a low potential of 258 mV at a current density of 10 mA cm⁻² and a Tafel slope of 46 mV dec⁻¹ in 1.0 M KOH solution. The present work provides the bimetallic phosphide nanoprism electrocatalyst with the tailored electronic structure for further application relevant to renewable energy exploration.     

Composition-controlled chemical bath deposition of Fe-doped NiO microflowers for boosting oxygen evolution reaction

Water electrolysis for green hydrogen production is gaining tremendous attention in the quest towards sustainable energy sources. At the heart of water splitting technology are the electrocatalysts, which facilitate the two half-cell reactions, i.e., the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), with the latter being the most thermodynamically uphill. Herein, we managed to fabricate Ni_1-xFe_xO microflowers (μFs) with varying % of Fe doping (0 < x < 0.36) via an easy chemical bath deposition (CBD) method. The as-synthesized μFs drop-casted on graphene paper (GP) are then applied as electrocatalysts for OER. Compared to contrast catalysts, the electrocatalyst with x_Fe = 0.1 exhibits a lower overpotential of 297 mV at a current density of 10 mA cm⁻², Tafel slope of 44 mV dec⁻¹ and unprecedented turnover frequency of 4.6 s⁻¹ at 300 mV. It is believed that this remarkable electrochemical performance mainly stems from the synergistic effects of Ni and Fe species, working in harmony to enhance charge transfer kinetics and intrinsic activity of the catalyst. This work provides a promising avenue for developing cost-effective and highly active electrocatalysts as advanced electrodes for energy related applications.     

Nanosheet self-assembled NiCoP microflowers as efficient bifunctional catalysts (HER and OER) in alkaline medium

Developing greatly efficient and steady non-noble metal bifunctional electrocatalyst is of great significance for reducing the energy consumption. In this work, we found that the construction of hierarchical nanostructures was an effective strategy to improve the catalytic performance of bimetallic transition-metal phosphide (NiCoP). Herein, we successfully synthesized the Ni_1.5Co_1.5P catalyst with porous nanosheet self-assembled microflowers (MFs) structure by sequential solvothermal, annealing and phosphorization treatment, and then adjusted the morphology of the MFs by changing the Ni/Co molar ratio to optimize its electronic structure and increase the exposed active sites, thereby improving catalytic activity of the catalyst. Specifically, the Ni_1.5Co_1.5P/MFs only required overpotentials of 141 mV and 314 mV to reach a current density of 10 mA cm⁻² toward HER and OER, respectively. Impressively, during the continuous 12 h chronoamperometry measurement, the Ni_1.5Co_1.5P/MFs displayed good durability. In conclusion, this study provided a feasible strategy to explore and prepare low-cost non-noble metal bifunctional electrocatalysts.     

Efficient overall water splitting using nickel boride-based electrocatalysts

Currently there is tremendous interest in the discovery of low cost and efficient electrocatalysts for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). In this work, iron-doped nickel boride (Fe_xNi_1-xB) and nickel boride (NiB) were successfully grown on 3D self-supporting graphene (SSG) electrodes via a one-step reduction approach. The Fe_0.2Ni_0.8B/SSG electrode required a very low overpotential of only 263 mV for OER (the best OER activity achieved to date for a metal boride). NiB/SSG showed modest OER performance but excellent HER activity. A water electrolyzer comprising Fe_0.2Ni_0.8B/SSG and NiB/SSG delivered a current density of 10 mA cm⁻² at a voltage of only 1.62 V. Further, the Fe_0.2Ni_0.8B/SSG and NiB/SSG catalysts showed excellent stability with no deactivation observed over 14 h of testing. Results demonstrate that nickel boride-based electrocatalysts are promising lost cost alternatives to precious metal-based electrocatalysts for OER, HER and overall water splitting.     

Co-based MOF-derived Co/CoN/Co2P ternary composite embedded in N- and P-doped carbon as bifunctional nanocatalysts for efficient overall water splitting

In this work, we developed ternary metallic cobalt-cobalt nitride-dicobalt phosphide composite embedded in nitrogen and phosphorus co-doped carbon (Co/CoN/Co₂P-NPC) as bifunctional catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The as-prepared Co/CoN/Co₂P-NPC is achieved by simultaneous annealing and phosphating of a Co–N rich metal-organic frameworks (MOFs) precursor. Compare with the phosphorus-free Co/CoN embedded nitrogen-doped carbon electrocatalyst (Co/CoN-NC), the as-prepared Co/CoN/Co₂P-NPC display superior HER and OER low overpotential of 99 mV and 272 mV at current density of 10 mA cm⁻². When Co/CoN/Co₂P-NPC electrocatalyst is use as bifunctional catalysts in overall alkaline water splitting, it exhibit excellent behaviour with 10 mA cm⁻² current at overall cell potential of 1.60 V. The excellent performance of Co/CoN/Co₂P-NPC electrocatalyst is attributed to the phosphating process that could further enhance synergistic effect, create stronger electronic interactions, and form efficient dual heteroatom doping to optimize the interfacial adhesion within the electrocatalyst. This present work will create more opportunities for the development of new, promising and more active sites electrocatalysts for alkaline electrolysis.     

Bifunctional electrocatalysts of CoFeP/rGO heterostructure for water splitting

Bifunctional non-precious electrocatalysts with high performance are highly desired for renewable energy but remain challenging. Herein, a CoFeP/rGO heterostructure was rational developed based on the synergistic effect, including superior conductivity, increased catalytic active sites of rGO support and the regulated electron distribution of bimetallic phosphide. At a current of 10 mA cm^?2, the CoFeP/rGO-2 composite exhibits excellent HER activity with low overpotentials of 101 mV and 76 mV in 1.0 M KOH and 0.5 M H₂SO₄ electrolyte, respectively. And highly active alkaline OER performance was provided with an overpotential of only 275 mV to reach a current density of 10 mA cm^?2. By the way, the CoFeP/rGO-2 electrode showed a pleasured working voltage of 1.58 V for overall water splitting in alkaline environment. More importantly, the long term durability and higher stability of the catalysts demonstrated their feasibility of bimetallic phosphide/rGO system as bifunctional electrocatalysts.     

Crystalline nickel sulfide integrated with amorphous cobalt sulfide as an efficient bifunctional electrocatalyst for water splitting

The development of highly efficient and low-cost electrocatalysts is critical to the mass production of hydrogen from water splitting. Herein, a facile yet effective method was developed to synthesize bimetallic sulfides Ni₃S₂/CoS_x, which were aimed for use as the electrocatalysts in both HER and OER. Encouragingly, the Ni₃S₂/CoS_x demonstrated a low overpotential of 110 mV for HER at a current density of 10 mA·cm^?2. It was discovered that the surface of Ni₃S₂/CoS_x during OER process would undergo an in-situ oxidation to form MOOH (M = Co, Ni), that is, MOOH/Ni₃S₂/CoS_x were the real functioning species in catalysis, which had an excellent OER activity and a low overpotential of 226 mV. Additionally, the assembled electrolyzer required only a low cell voltage of 1.53 V to achieve a current density of 10 mA·cm^?2 in a 1 M KOH solution, and its performance was stable. Overall, this work provided a promising strategy for the facile fabrication of low-cost amorphous electrocatalysts, which is expected to promote the progress of overall water splitting.     

Enhanced OER performance of NiFeB amorphous alloys by surface self-reconstruction

The design and development of cost-effective and highly efficient oxygen evolution reaction (OER) electrocatalysts are urgently desirable during the water-splitting process. Here, Ni_xFe_80-xB₂₀ (x = 70, 60, 50, 40, 30, hereafter referred to as NFB) amorphous alloys, with high mechanical strength, excellent corrosion resistance, and unique atomic structure, are fabricated as efficient water oxidation electrocatalysts in alkaline solutions. Ni₄₀Fe₄₀B₂₀ amorphous ribbons achieve only 319 mV of overpotential at 10 mA·cm^?2 with a Tafel slope of 56 mV dec^?1 and exhibit excellent long-term stability for 24 h at 10 mA·cm^?2 and 100 mA·cm^?2 in 1 M KOH solution, which outperform the commercial RuO₂ electrocatalyst. It is worth noting that the OER performance of Ni_xFe_80-xB₂₀ amorphous electrocatalysts after long-term chronopotentiometry test displays more effectively, which can be ascribed to the surface construction. Meanwhile, the analysis of the morphology and structure of the electrocatalysts reveal that continuous oxidation during the OER process induces the structural reorganization on the surface of the electrocatalysts, which can enhance the electron transfer process and adsorption of the reaction intermediates to optimize the OER performance. This study provides a shred of evidence for surface self-reconstruction of NiFeB amorphous alloys electrocatalysts during the OER process and promotes the application of amorphous alloys as functional materials in the water-splitting field.     

Bimetallic phosphide nanoparticles embedded in carbon nanostrips for electrocatalytic water oxidation

The development of low-cost and stable catalysts to enhance the electrocatalytic performance of oxygen evolution reaction (OER) has long been a concern. Herein, the rational synthesis of bimetallic phosphide nanoparticles anchored onto N-doped carbon of CoNiP/NC-X (X = 1, 2, 3 represent the molar ratio between Co and Ni of 1:1, 1:2, 2:1 in crystalline precursors, respectively) nanocomposites as high-performance electrocatalysts, which are calcined from a series of Co/Ni-based isostructural coordination polymers as the precursors. After pyrolysis, the as-obtained CoNiP/NC-1 nanostrips are intrinsically endowed with favorable nanostructure, large specific surface area, suitable heteroatom doping, abundant catalytic active sites and highly graphitic carbon network. Therefore, it exhibits a decent quasi-4-electron OER performance with a small overpotential of 330 mV at 10 mA cm^?2, a low Tafel slope of 80.5 mV dec^?1 and a 94.27% current retention after 10 hours in alkaline solution. The hierarchical nanostructures of CoNiP/NC-X series and their positive response to electrocatalytic properties have shed light on the preparation of other non-noble metal based carbon nanomaterials for efficient energy-related applications.     

Ultrathin MoS2 nanosheets in situ grown on rich defective Ni0.96S as heterojunction bifunctional electrocatalysts for alkaline water electrolysis

Developing earth-abundant and highly active bifunctional electrocatalysts are critical to advance sustainable hydrogen production via alkaline water electrolysis but still challenging. Herein, heterojunction hybrid of ultrathin molybdenum disulfide (MoS₂) nanosheets and non-stoichiometric nickel sulfide (Ni_0.96S) is in situ prepared via a facile one-step hydrothermal strategy, followed by annealing at 400 °C for 1 h. Microstructural analysis shows that the hybrid is composed of intimate heterojunction interfaces between Ni_0.96S and MoS₂ with exposed active edges provided by ultrathin MoS₂ nanosheets and rich defects provided by non-stoichiometric Ni_0.96S nanocrystals. As expected, it is evaluated as bifunctional electrocatalysts to produce both hydrogen and oxygen via water electrolysis with a hydrogen evolution reaction (HER) overpotential of 104 mV at 10 mA cm⁻² and an oxygen evolution reaction (OER) overpotential of 266 mV at 20 mA cm⁻² under alkaline conditions, outperforming most current noble-metal-free electrocatalysts. This work provides a simple strategy toward the rational design of novel heterojunction electrocatalysts which would be a promising candidate for electrochemical overall water splitting.     

NiFe layered double hydroxide nanosheet arrays for efficient oxygen evolution reaction in alkaline media

Exploring efficient oxygen evolution reaction (OER) catalysts synthesized from low-cost and earth-abundant elements are crucial to the progression of water splitting. In this paper, NiFe layered double hydroxide (LDH) nanosheets were grown on Ni foam (NF) through a straightforward hydrothermal method. The Fe doping effects were systematically investigated by controlling Ni/Fe ratios and Fe valence states, and the in-depth influence mechanisms were discussed. The results indicate that, through controlling structure morphology and enhancing Ni²⁺ oxidation, NiFe_III(1:1)-LDH displays the best and outstanding OER performance, with a low over potential of 382 mV at 50 mA cm^?2, a low Tafel slope of 31.1 mVdec^?1 and only 20 mV increase after 10 h continuous test at 50 mA cm^?2. To our knowledge, this is one of the best OER electrocatalysts in alkaline media to date. This work provides a facile and novel strategy for the fabrication of bimetallic LDH catalysts with desired structures and compositions.     

The influence of increased content of Ni(III) in NiFe LDH via Zn doping on electrochemical catalytic oxygen evolution reaction

Developing efficient oxygen evolution electrocatalysts always shows great importance in the field of electrolysis of water. In this work, Zn-doped NiFe LDH is synthesized via a facile hydrothermal reaction. A series of structural characterizations revealed that the doping of Zn into NiFe LDH lattice can cause lattice distortion, which facilitates the formation of active NiOOH layers. The Zn–NiFe LDH electrocatalyst shows excellent performance in electrocatalytic oxygen evolution reaction, even overbeat the state-of-art RuO₂. In addition, the doping of Zn into NiFe LDH significantly enhances the electrocatalytic stability of NiFe LDH, with only a 32.7 mV increase in potential after 100 h continuous OER electrolysis in 1.0 M KOH. The Zn–NiFe LDH provides an ideal strategy for designing highly efficient OER electrocatalysts for real applications.     

AC magnetic field enhancement oxygen evolution reaction of bimetallic metal-organic framework

Cost-effective oxygen evolution reaction (OER) electrocatalysts play a key role in electrocatalytic water splitting process. Here, a facile and scalable strategy was applied to synthesize the bimetallic metal-organic frameworks (MOFs) with high OER activity, and the effects of AC magnetic field on OER was also investigated. Results shows that the bimetallic MOFs (Co_0.4Ni_0.6-MOF-74) exhibited a three-dimensional flower-like morphology, and possessed a higher BET specific area of 905.39 m² g^?1 as well as a smaller median pore size of 0.49 nm as compared to single metal MOFs; It owned a lowest overpotential of 314 mV at 10 mA cm^?2 and Tafel slope of 79.39 mV dec^?1, both are much lower than these of single metal MOFs, being due to the high specific area and more active sites derived from the distorted crystal structure; When AC magnetic field strength equaled to 5.50 mT, overpotential at 10 mA cm^?2 for Co_0.4Ni_0.6-MOF-74 reached minimum value of 201 mV, reduced by about 36% as compared to that without magnetic field, indicated that AC magnetic field could greatly improve OER process. These improvements resulted from the spin polarization effect, magnetohydrodynamic (MHD) convection and improved active point temperature.     

Self-supported Ni2P nanotubes coated with FeP nanoparticles electrocatalyst (FeP@Ni2P/NF) for oxygen evolution reaction

Bimetallic phosphides have been widely investigated as electrocatalysts for oxygen evolution reaction (OER) due to their efficient activity and environmental friendliness. While the reasonable design and controllable synthesis of bimetallic phosphide with typical nanostructure is still a great challenge. Hence, we put forward a novel and straightforward way for constructing FeP nanoparticles coated Ni₂P ultrathin nanotube arrays on the surface of Ni foil (FeP@Ni₂P/NF), which is synthesized through two steps of electrodeposition and subsequent in-situ phosphorization process. The obtained FeP@Ni₂P/NF shows excellent electrochemical activity for OER, and it only needs potential of 1.52 V vs. RHE to reach the current density of 50 mA cm⁻² in an alkaline media. The excellent electrocatalytic activity of FeP@Ni₂P/NF mainly benefits from: (i) the synergistic effect between FeP and Ni₂P promoting electron transfer; (ii) the formation of the unique 3D ultrathin nanotube arrays increasing the quantity of active sites and avoiding the agglomeration of catalysts during testing. In addition, the influence of reaction condition on the electrochemical activity for OER has also been investigated through altering the phosphorization temperature of precursor.     

Enriched oxygen vacancy promoted heteroatoms (B,P, N,and S) doped CeO2: Challenging electrocatalysts for oxygen evolution reaction (OER) in alkaline medium

Increasing worldwide energy consumption has prompted considerable study into energy generation and energy storage systems in recent years. Chemical fuels may be produced efficiently via electrocatalytic water splitting, which uses electric and solar power. The development of efficient anodic electrocatalysts for efficient oxygen evolution reaction (OER) is a greater concern of present energy research. Cerium oxide (CeO₂) are promising electrocatalysts that exhibit outstanding OER but their reduced stability obstructs the practical application. A novel strategy was established to construct an effective catalyst of heteroatom (N, B, P and S) doped CeO₂ matrix were prepared. Moreover, the doping of heteroatoms into the CeO₂ matrix processes the improved electronic conductivity, reactive sites, increases the electrochemical catalytic activity, which enhances the water oxidation reaction. Consequently, well-suited alkaline electrolysers were brought together for water oxidation to ideal OER electrocatalytic activity. The OER activity of the electrocatalysts follows the order of S–CeO₂ (190 mV@10 mA cm⁻²), N– CeO₂ (220 mV @10 mA cm⁻²), P– CeO₂ (230 mV @10 mA cm⁻²), B–CeO₂ (250 mV @10 mA cm⁻²) and CeO₂ (260 mV @10 mA cm⁻²) in 1 M of KOH. From the kinetics analysis, Tafel slope value achieved for catalysts CeO₂, B–CeO_2, P–CeO₂, N–CeO₂ and S–CeO₂ are 142 mV dec⁻¹,121 mV dec⁻¹, 102 mV dec⁻¹, 98 mV dec⁻¹ and 83 mV dec⁻¹ respectively. These results validate that the S–CeO₂ electrode is prominent for OER performance with the requirement of cell voltage of 1.42 V at 10 mA cm⁻² current density. In addition, sulphur doped CeO₂ relatively have excellent stability through chrono-potentiometric analysis lasting for 20 h. Although the heteroatoms doped CeO₂ is acts as anode material, the preparation method is widespread, which will reduce the synthesis cost and streamline the preparation of electrode for OER. This research effort delivers a complete advantage for the development of robust, environmentally friendly and highly dynamic electrocatalysts for OER activity.