Electrocatalyst For Efficient Water Splitting Research Articles

Multi-interfacial Ni/Mo2C ultrafine hybrids anchored on nitrogen-doped carbon nanosheets as a highly efficient electrocatalyst for water splitting

Interfacial engineering in the rapid development of high-performance electrocatalysts for water splitting has been explored as a promising strategy to improve catalytic performance due to the tunable free energy of reaction intermediates on the interfacial compositions. Here, multiple-interfacial Ni/molybdenum carbide hybrid nanoparticles embedded in N-doped carbon nanosheets (Ni/Mo2C@NC) electrocatalyst were fabricated via a solid-state co-reduction method. The as-synthesized catalyst exhibits excellent hydrogen evolution reaction (HER) activity with an overpotential of 91 mV at 10 mA/cm2 and a Tafel slope of 74 mV/dec in alkaline solution, and outstanding stability owing to the high conductivity, abundant interfacial active sites, and synergistic effect between Ni and Mo2C nanoparticles. This electrocatalyst as bifunctional electrode possesses an applied voltage of 1.64 V at 10 mA/cm2 and long-term durability in an electrolysis cell. Moreover, density functional theory calculations reveal that the electron transfer across Ni/Mo2C heterointerfaces could optimize the water adsorption/dissociation and H adsorption/desorption capacities, thereby boosting the intrinsic HER activity.

In-situ growth of ruthenium-based nanostructure on carbon cloth for superior electrocatalytic activity towards HER and OER

The control in synthesis and composition plays a vital role in exploring cost-effective efficient electrocatalysts for water splitting. This paper reported a glycerol-assisted solvothermal strategy to synthesize Ru-based electrocatalyst (Ru-G/CC), in-situ growing Ru nanoparticles (NPs) on carbon cloth (CC). The optimal Ru-G/CC exhibits a boosted HER activity (overpotential of 40 mV @ 10 mA cm−2, Tafel slope 76 mV dec−1), surpassing benchmark 20 wt% Pt/C; experimental characterization and DFT calculations verified that Ru NPs with a mixed amorphous/crystalline structure in Ru-G/CC effectively decrease the reaction energy barrier in HER. Also, the hydrothermally derived Ru-H2O/CC-350 exhibited a high electrocatalytic OER activity (overpotential of 270 mV @ 10 mA cm−2, Tafel slope 63 mV dec−1), exceeding the commercial RuO2. This work provides a successful story via regulating synthetic parameters to design efficient and stable Ru-based electrocatalysts for water splitting.

PANI-coated porous FeP sheets as bifunctional electrocatalyst for water splitting

Polyaniline (PANI) coated porous iron phosphide (PANI/p-FeP) supported on nitrogen‑doped carbon fiber/carbon paper (PANI/p-FeP/NCF/CP) is prepared as a high efficient electrocatalyst for water splitting. The synergistic effect between PANI coating and underlying porous FeP not only affords richly exposed active sites, but also modulates the electronic structure of FeP and thus accelerates the charge or mass transfer efficiency, which eventually improves the catalytic activity. The self-supported PANI/p-FeP/NCF/CP composite requires low overpotentials of 59 and 76 mV at 10 mA cm−2 current density in 0.5 M H2SO4 and 1.0 M KOH for hydrogen evolution reaction (HER). Otherwise, PANI/p-FeP/NCF/CP only requires an overpotential of 355 mV at 10 mA cm–2 in 1.0 M KOH for oxygen evolution reaction (OER). PANI/p-FeP/NCF/CP exhibits good durability for HER and OER due to the protective effect of PANI coating in the electrochemical process.

An efficient Fe2O3/FeS heterostructures water oxidation catalyst

Slow kinetics and insufficient understanding of the perceptual design of oxygen evolution reaction (OER) electrocatalysts are major obstacles. Overcoming these challenges, heterostructures have recently attracted attention because they encourage alternative OER electrocatalysts with active structural features. In this study, synthesis, characterization and electrochemical evaluation of the heterostructure of iron oxide/iron sulfide (Fe2O3/FeS) and its counterparts, iron oxide (Fe2O3) and iron sulfide (FeS) are reported. The structural features of as-synthesized electrocatalysts have been evaluated by infrared spectroscopy, powder X-ray diffraction study and scanning electron microscopy. Fe2O3/FeS was found to be a stable electrocatalyst for efficient water splitting, which initiates OER at a surprisingly low potential of 1.49 V (vs RHE) in 1 M potassium hydroxide. The Fe2O3/FeS electrocatalyst drives OER with a current density of 40 mA cm−2 at overpotential of 370 mV and a Tafel slope of 90 mV dec−1. Its performance is better than its counterparts (Fe2O3 and FeS) under similar electrochemical conditions. At an applied potential of 1.65 V (vs RHE), continuous oxygen production for several hours revealed the long-term stability and effective activity of the Fe2O3/FeS electrocatalyst for OER. The as-developed Fe2O3/FeS heterostructure provides an effective alternative low-cost metal-based electrocatalysts for OER.

A novel in-situ strategy develops for Mo2C nanoparticles incorporated on N, P co-doped stereotaxically carbon as efficient electrocatalyst for overall water splitting

Developing cost-effective and remarkable electrocatalysts toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performs excelling role in boosting the hydrogen energy application. Herein, a novel in-situ one-pot strategy is developed for the first time to synthesize molybdenum carbide nanoparticles (Mo2C NPs) incorporated on nitrogen (N) and phosphorous (P) co-doped stereotaxically carbon (SC). The optimized Mo2C NPs/N, P–SC–800 electrocatalyst exhibits lower overpotentials of 131 and 287 mV for HER and OER to deliver a current density of 10 mA cm−2 in 1.0 M KOH medium with smaller Tafel slopes of 58.9 and 74.4 mV/dec, respectively. In addition, an electrolyzer using Mo2C NPs/N, P–SC–800 electrode as cathode and anode delivers a current density of 10 mA cm−2 at a small voltage of 1.64 V for overall water splitting. The excellent water splitting performance could be ascribed to optimum Mo2C NPs for more accessible active sites, highly active N, P-SC networks for accelerated electron transfers, and synergetic effect between Mo2C NPs and N, P-SC networks. The N, P-SC network not only enhances the overall dispersion of Mo2C NPs but also contributes numerous electroactive edges to enhance the performance of HER, OER, and overall water splitting activity. This research work explores the in-situ one-step strategies of advanced, cost-effective, and non-precious metal electrocatalysts for efficient water splitting and motivates the consideration of a novel class of heteroatom doped stereotaxically carbon nanocomposites for sustainable energy production.

General synthesis of Pt and Ni co-doped porous carbon nanofibers to boost HER performance in both acidic and alkaline solutions

It is essential to develop efficient electrocatalysts to generate hydrogen from water electrolysis for hydrogen economy. In this work, platinum (Pt) and nickel (Ni) co-doped porous carbon nanofibers (Pt/Ni-PCNFs) with low Pt content were prepared via an electrospinning, carbonization and galvanic replacement reaction. Because of the high electrical conductivity, abundant electrochemical active sites and synergistic effect between Pt and Ni nanoparticles, the optimized Pt/Ni-PCNFs catalyst shows an excellent HER activity with overpotentials of 20 mV in 0.5 mol/L H2SO4 and 46 mV in 1 mol/L KOH at a current density of 10 mA/cm2. Furthermore, over 35-h long-term stability has been achieved without significant attenuation. This work provides a simple route to prepare highly efficient electrocatalysts for water splitting and has great prospects in the field of renewable energy.

Molybdenum carbide (Mo2C) and reduced graphene oxide (rGO) nano-composites as an efficient electrocatalyst for water splitting

Hydrogen is one of the most promising renewable energy for production and storage to replace the fossil fuel and petroleum-based energy sources. Here, we prepared and used transition metal carbide (TMC) composite with the rGO (reduced graphene oxide) such as Mo2C-rGO to replace the platinum-based electrode. The synthesis of the composite involves a wet chemical method followed by a high-temperature carbonization treatment that led to the crystallization of the molybdenum precursor to molybdenum carbide and the graphene oxide to reduced graphene oxide (rGO). Microstructure analysis revealed the dispersion of Mo2C nanoparticles over rGO that achieved excellent HER (hydrogen evolution reaction) performance with an onset potential of −88 mV, better Tafel slope (67 mV dec−1) and outstanding stability. The HER performance was compared with composites prepared at different carbonization temperatures (750 °C–1050 °C) and with Mo2C-MOF (metal organic framework) and Mo2C-carbon black composite.

Vacancy-mediated transition metals as efficient electrocatalysts for water splitting.

Water splitting using renewable electricity provides a promising way for large-scale hydrogen production due to its zero-carbon emission properties. However, the development of highly efficient, low-cost and durable electrocatalysts remains an ongoing challenge in industrial applications. Herein, a strategy integrating vacancy engineering and metal doping was proposed to design and screen M@CuS catalysts with excellent catalytic activity via density functional theory (DFT) calculations. TM single atoms anchored by the vacancy of the CuS surface show high stability, and serve as the active centers for water splitting. Ti@CuS and Co@CuS exhibit exceptional performance towards the hydrogen evolution reaction (HER). Ti@CuS and Co@CuS can achieve hydrogen adsorption free energies (ΔGH*) of 0.01 eV and -0.03 eV, respectively. The HER process of Ti@CuS is controlled by the Heyrovsky mechanism. Co@CuS also shows superior catalytic activity towards the oxygen evolution reaction (OER), and presents a relatively lower OER overpotential of 0.41 V. Co@CuS serves as a promising candidate of bifunctional HER/OER electrocatalysts. This work not only provides highly efficient electrocatalysts for water splitting, but also inspires a novel concept to guide the extending design of catalysts in other catalysis fields.

Computational screening of transition-metal doped boron nanotubes as efficient electrocatalysts for water splitting.

The search for efficient and low-cost electrocatalysts for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is of utmost importance for the production of hydrogen and oxygen via water splitting. In this work, the catalytic performance of the OER and HER on transition metal doped boron nanotubes (BNTs) was investigated using density functional theory. It was found that the doped transition metal atoms determine the catalytic activity of the BNTs. Rhodium-doped BNTs exhibited excellent OER activity, while cobalt-doped BNTs displayed great catalytic activity toward the HER. Volcano relationships were found between the catalytic activity and the adsorption strength of reaction intermediates. Rhodium- and cobalt-doped BNTs exhibited great OER and HER catalytic activity due to the favorable adsorption strength of reaction intermediates. This work sheds light on the design of novel electrocatalysts for water splitting and provides helpful guidelines for the future development of advanced electrocatalysts.

Iron and chromium co-doped cobalt phosphide porous nanosheets as robust bifunctional electrocatalyst for efficient water splitting

It is still a huge challenge to develop highly efficient and low-cost non-precious metal-based electrocatalysts for overall water splitting in alkaline electrolytes. Herein, Cr and Fe co-doped CoP porous mesh nanosheets (Mesh-CrFe-CoP NSs) were synthesized through hydrolysis reaction, ion exchange etching and subsequent low-temperature phosphating process. The Mesh-CrFe-CoP NSs provides overpotentials at a current density of 10 mA cm−2 under alkaline electrolyte of 103.7 mV and 256.4 mV for HER and OER, respectively. Furthermore, when using Mesh-CrFe-CoP NSs as anode and cathode, the water splitting system could afford a current density of 10 mA cm–2 at 1.55 V, which is better than an electrolytic cell composed of 20% Pt/C and RuO2. The excellent electrocatalytic performance of Mesh-CrFe-CoP NSs is attributed to the co-doping and porous nanostructure. Specifically, the Cr and Fe co-doped porous CoP nanosheets electrocatalyst not only provided abundant exposure active sites, accelerated the entry of liquid and the diffusion of gas, but also regulated the electronic environment of active sites, and thus enhanced the electrochemical performance. This work proposes a strategy for the rational design of highly efficient and stable non-precious metal co-doped phosphide electrocatalysts in the of electrochemical water splitting.

Structural and Componential Engineering of Co2P&CoP@N-C Nanoarrays for Energy-Efficient Hydrogen Production from Water Electrolysis.

The development of electrocatalysts for efficient water splitting is a pivotal and challenging task. Transition-metal phosphides (TMPs) have been known as one of the most promising candidates for the efficient hydrogen evolution reaction (HER) due to their favorable intrinsic reactivity. However, structural engineering related to the gas bubbles evolution and tiny regulation of components concerned with the electronic structure remained as a significant challenge that requires further optimization. Herein, the nanoarrays (NAs) composed of ultrasmall Co2P and CoP nanoparticle-embedded N-doped carbon matrix (Co2P&CoP@N-C) are prepared and demonstrated an overpotential of 62.8 ± 4.7 mV at 10 mA cm-2 in 1.0 M KOH. The nanoarray-structured electrocatalyst revealed the superaerophobicity and facilitates the detachment of the in situ formed hydrogen gas bubbles, ensuring abundant catalytic sites and electrode-electrolyte interface for the mass transfer process. The amount of P doping modulated the local electron density around Co and P atoms, which attains a favorable compromise to afford sufficient electrons for the electrocatalysis and inhibit the negative influence of H2 desorption. Significantly, the lowered overpotential induced by the electrocatalyst surface architecture is much stronger than that of the component content and promotes the electrocatalytic activity.

CoNiCuMgZn high entropy alloy nanoparticles embedded onto graphene sheets via anchoring and alloying strategy as efficient electrocatalysts for hydrogen evolution reaction

Great interests have been focused on high entropy alloys, a new class of single-phase solid solution materials, because of their unique physical and chemical properties. Herein, CoNiCuMgZn high entropy alloy (HEA) has been homogeneously embedded onto ultrathin two-dimensional (2D) holey graphene conducting substrates via a simple anchoring and alloying strategy. During the growth of the HEA, graphene oxide is employed as both direct template and reductant. By modulating the initial input amounts of metal sources, the particle sizes of HEA can be finely regulated from 40 to 200 nm. Benefiting from the synergistic effect between the excellent electronic conductivity of graphene and the abundant catalytic sites of HEA particles, the obtained material displays remarkable catalytic activity and stability for hydrogen evolution reaction compared to previous reported non-noble-metal catalysts. The density functional theory calculation unveils that the unique embedded structure of HEA onto graphene benefits to the H* sorption and promotes the catalytic kinetics. This work is of great importance in the practical utilization of HEA and indeed give a brilliant perspective in fabricating HEA as efficient electrocatalysts for water splitting.

Mini review on H2 production from electrochemical water splitting according to special nanostructured morphology of electrocatalysts

Hydrogen is one of the most promising alternative energy resources of fossil fuels. Among the many ways to generate hydrogen gas, electrochemical water splitting is more feasible and renewable. Compared to processes using solar energy for a specific geological environment or thermochemical decomposition at high temperatures, the electrocatalysis of water can produce hydrogen without the restriction of geological conditions and scale-up facilities. Water is one of the most renewable and sustainable resources to obtain hydrogen. On the other hand, water splitting into hydrogen and oxygen is thermodynamically unfavorable under the atmospheric condition. Therefore, novel materials are needed to produce hydrogen from water splitting using electrocatalysts. Recently, various state-of-the-art technologies and catalysts have been developed in the electrocatalysis of water to produce hydrogen. Among the litany of novel materials, according to the preparation method and morphology of electrocatalysts, the hydrogen production efficiency from water splitting shows great differences. This paper recently reported efficient electrocatalysts for water splitting using multi-component catalysts composed of several metals, organic polymer, metal sulfides, and metal phosphides. In addition, the essential principles for an investigation regarding more efficient hybrid electrocatalysts for water splitting as a renewable and sustainable hydrogen producing method can be determined.

Bifunctional heterostructured nitrogen and phosphorus co-doped carbon-layer-encapsulated Co2P electrocatalyst for efficient water splitting

Highly efficient and robust non-noble bifunctional electrocatalysts with excellent stability are essential for practical large-scale application of hydrogen energy. Here, we design a hybrid nanostructure of Co2P nanoparticles encapsulated uniformly within N, P co-doped carbon layers that are then integrated into conductive carbon cloth (N-Co2P/NPC). As expected, the developed electrode exhibits very low overpotentials of 68 and 230 mV at 10 mA cm−2 for the hydrogen evolution reaction and oxygen evolution reaction, respectively. Density functional theory calculations reveal that the electronic structure of Co2P can be tailored effectively via the N-doping effect, with the d-band center shifting to a negative position compared with that at the Fermi level, leading to optimized adsorption interaction with hydrogen evolution reaction (HER)/oxygen evolution reaction (OER) intermediates. Furthermore, a stable solar-to-hydrogen conversion efficiency of 17.9% is achieved with a solar-driven water splitting electrolyzer.

Comparing electrocatalytic hydrogen and oxygen evolution activities of first-row transition metal complexes with similar coordination environments

Developing cheap and efficient electrocatalysts for water splitting is required for energy conversion techniques. Many first-row transition metal complexes have been shown to be active for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Metal ions play crucial roles in these catalytic processes, but the activity dependence on the nature of metal ions has been rarely studied due to the difficulty to compare metal complexes with different coordination environments. We herein reported the synthesis of a series of metal complexes of azido-substituted porphyrin (1), in which metal ions have very similar coordination environments. By grafting 1-M (M = Mn, Fe, Co, Ni, and Cu) onto alkyne-functionalized carbon nanotubes (CNTs) through the same covalent connection, the resulted hybrids 1-M@CNT were all active and robust for both electrocatalytic HER and OER in alkaline aqueous solutions. Among these hybrids, 1-Fe@CNT displayed the highest electrocatalytic activity for HER, while 1-Co@CNT was the most active one for OER. Moreover, a two-electrode water electrolysis cell assembled with 1-Fe@CNT as the cathode and 1-Co@CNT as the anode required smaller applied bias potential by 210 mV to get 10 mA/cm2 current density as compared to that assembled with Pt/C and Ir/C with the same amount of metal loading. This work is significant to correlate HER and OER activity with the nature of first-row transition metal ions and to highlight promising potential applications of molecular electrocatalysis in water splitting.

Co-metal–organic framework derived CoSe2@MoSe2 core–shell structure on carbon cloth as an efficient bifunctional catalyst for overall water splitting

Electrocatalytic water splitting is a very promising and sustainable approach for generating hydrogen as a clean carbon-free fuel. To develop an efficient electrocatalyst for water splitting, the overpotential for this reaction must be minimized by using a capable electrocatalyst that can support the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). In this study, we prepared a unique core–shell structure, Co-metal–organic framework (MOF) derived cobalt diselenide laminated with molybdenum diselenide (MOF-CoSe2@MoSe2) and assessed its performance as a bifunctional electrocatalyst for the HER and OER in alkaline media. The CC/MOF-CoSe2@MoSe2 core–shell structure fabricated directly on a flexible carbon cloth substrate demonstrated low overpotentials (η10) of 109.87 and 183.81 mV for the HER and OER, respectively, and a low voltage of 1.53 V for overall water splitting activity with an electrolyzer cell with symmetric CC/MOF-CoSe2@MoSe2 electrodes. The developed CC/MOF-CoSe2@MoSe2 catalyst had excellent stability over 24 h for OER, HER, and overall water splitting activity. These results suggest that lamination of MOF with a transition metal dichalcogenide is an effective route for developing the highly efficient and sustainable bifunctional electrocatalyst for overall water splitting activity.

W-induced morphological modification of NiFe layered double hydroxides as efficient electrocatalysts for overall water splitting

Layered double hydroxides (LDHs) are one of the most efficient electrocatalysts for water splitting due to their nanosheet features and compositional flexibilities. This work explored the impact of W precursor concentration (0 ∼ 10 mM) on LDH morphologies and performance in hydrogen production. Using an electrodeposition W-doping process, W-induced NiFe LDHs (NiFeW-LDHs) were in-situ grown on carbon fiber papers for water splitting. A performance peak was found at a W doping of 5 mM with well-aligned nanosheets, which not only boosted the charge transfer ability and gas evolution but also offered more than a four-fold electrochemical surface area increase compared to film-like NiFe hydroxides. The NiFeW-LDHs exhibited remarkable performance compared to NiFe hydroxides, showing decreased overpotentials of 31 mV and 114 mV for the oxygen evolution reactions (OERs) and hydrogen evolution reactions (HERs) at 10 mA/cm2 and -10 mA/cm2, respectively, in alkaline media. The performance enhancement at 5 mM W-doping was linked to the well-aligned NiFeW-LDH nanosheets; smaller, less-textured nanosheets were observed with lower or higher W precursor concentrations (2.5 mM or >7.5 mM), leading to inferior OER and HER performances. Hence, an appropriate W doping is crucial to generating the morphologies that contribute to the higher performance of NiFeW-LDHs.

Novel urchin-like CoNiP as advanced pH-universal electrocatalysts toward hydrogen evolution reaction

Electronic structure and morphology modulation are challenging for the construction of efficient electrocatalysts towards water splitting. Herein, a facile hydrothermal strategy and subsequent phosphorization process are utilized to synthesize urchin-like CoNiP integrated by nanowires. The synthesized urchin-like CoNiP can be applied as electrocatalysts for hydrogen evolution reaction (HER) in alkaline, neutral, and acidic media. In particular, the optimal urchin-like CoNiP exhibits superior HER activity in alkaline electrolytes, with small overpotentials (157, 317, and 437 mV) at the current density 10, 100, and 200 mA cm−2, respectively, and a small Tafel slope (49.6 mV dec−1) in 1 M KOH, which is comparable to that of Pt/C catalyst. Moreover, when urchin-like CoNiP is employed as both the cathode and anode in 1 M KOH, a low cell overpotential of 490 mV is required to reach the current density of 10 mA cm−2, suggesting the efficient electrocatalyst toward overall water splitting. The superior performance of urchin-like CoNiP can be associated with the sharp-tip enhancement effect since the hierarchical structure composed of nanowires with high curvature tips benefits the accumulation of electrons on the tip of the nanowires to serve as effectively active sites for reactions and the mass transfer, as well as the fast electron transfer due to the good electrical conductivity of the bimetallic phosphide. This work opens up a promising approach to rationally construct low-cost and efficient electrocatalysts for water splitting.

Nickel-cobalt phosphate nanoparticles wrapped in nitrogen-doped carbon loading on partially phosphatized foamed nickel as efficient electrocatalyst for water splitting

The progress in the development of 3D self-supporting electrocatalysts is of great significance for the practical application of water electrolysis. In this work, a self-supporting transition metal phosphate was prepared, in which nickel–cobalt phosphate (NixCo1-x(PO3)2) nanoparticles wrapped in nitrogen-doped carbon (NC) were supported on partially phosphatized foamed nickel (P-NF). The particles of ZIF-67-derived Co-N co-doped carbon were fixed on NF by electroplating Ni. The following phosphating led to the NixCo1-x(PO3)2 particles wrapped in NC loading on P-NF (NiCoPO@NC/P-NF-e). The NixCo1-x(PO3)2 nanoparticles could effectively afford active sites and exhibited preeminent catalytic activity. Also, NC could improve the electrical conductivity of the sample, accelerate the transfer and transport of charge and prevent the corrosion of electrolyte to NixCo1-x(PO3)2 particles. The NiCoPO@NC/P-NF-e catalyst exhibited outstanding catalytic performances for oxygen evolution reaction in 1 M KOH and wide-pH hydrogen evolution reaction. A voltage of 1.50 V was required to reach 10 mA cm−2 for water splitting. Besides, the NiCoPO@NC/P-NF-e catalyst showed superior durability for electrolysis of water. The work completed in this study provides a potential methodology for preparing 3D self-supporting phosphate catalysts.

CoFeP hierarchical nanoarrays supported on nitrogen-doped carbon nanofiber as efficient electrocatalyst for water splitting

Developing high-efficient bifunctional electrocatalysts is significant for the overall water splitting. Bimetallic phosphides show great potential for the bifunctional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts due to the excellent catalytic performance. Herein, the CoFeP two-dimensional nanoarrays successfully grown on nitrogen doped electrospun carbon nanofibers (CoFeP NS@NCNF) through template-directed growth and following phosphorization treatment. Benefiting from the hierarchical nanoarrays structure, synergistic effect of high electrical conductivity carbon nanofiber substrate and bimetallic phosphide, the CoFeP NS@NCNF exhibits efficient bifunctional electrocatalytic activities for OER and HER in 1 M KOH with overpotentials of 268 mV (η20) and 113 mV (η10), respectively. Moreover, the CoFeP NS@NCNF coupled two-electrode system needs a low voltage of 1.59 V at 10 mA cm−2 for overall water splitting. This work provides a promising way for the preparation of transition metal-based electrocatalysts with hierarchical structure derived from Prussian blue analogues (PBAs) for OER and HER.