Electrocatalysts For Water Splitting Research Articles

Fe‐doped Ni3S2@CoSx nanoarrays derived from MOF as bifunctional electrocatalysts for efficient overall water splitting

AbstractBackgroundFabricating high‐performance bifunctional electrocatalysts remains challenging to promote the development of electrocatalytic water splitting.ResultA heterostructure Fe‐Ni3S2@CoSx/NF was successfully synthesized by using interfacial engineering strategy. Benefiting from the strong synergistic effect between highly active CoSx and Fe‐Ni3S2, Fe‐Ni3S2@CoSx/NF exhibited outstanding bifunctional performance, which showed low overpotentials of 77 mV for HER and 217 mV for OER at 10 mA cm−2, respectively.ConclusionThe CoSx nanoarrays and Fe‐Ni3S2 nanosheets respectively served as HER and OER active center. When Fe‐Ni3S2@CoSx/NF was used as both cathode and anode for overall water splitting, a low voltage of 1.52 V was required to reach the current density of 10 mA cm−2 with nearly 100% Faradic efficiency and outstanding durability.This article is protected by copyright. All rights reserved.

Powering the Future by Iron Sulfide Type Material (FexSy) Based Electrochemical Materials for Water Splitting and Energy Storage Applications: A Review.

Water electrolysis is among the recent alternatives for generating clean fuels (hydrogen). It is an efficient way to produce pure hydrogen at a rapid pace with no unwanted by-products. Effective and cheap water-splitting electrocatalysts with enhanced activity, specificity, and stability are currently widely studied. In this regard, noble metal-free transition metal-based catalysts are of high interest. Iron sulfide (FeS) is one of the essential electrocatalysts for water splitting because of its unique structural and electrochemical features. This article discusses the significance of FeS and its nanocomposites as efficient electrocatalysts for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), and overall water splitting. FeS and its nanocomposites have been studied also for energy storage in the form of electrode materials in supercapacitors and lithium- (LIBs) and sodium-ion batteries (SIBs). The structural and electrochemical characteristics of FeS and its nanocomposites, as well as the synthesis processes, are discussed in this work. This discussion correlates these features with the requirements for electrocatalysts in overall water splitting and its associated reactions. As a result, this study provides a road map for researchers seeking economically viable, environmentally friendly, and efficient electrochemical materials in the fields of green energy production and storage.

Transition Metal‐Cross‐Linked‐Starch Aerogel‐Derived Porous Carbon‐Based Monolithic Chainmail Electrodes for High‐Current‐Density and Durable Alkaline Water Splitting

AbstractA porous carbon‐based monolithic chainmail electrode, namely Co2P@CSA, is fabricated via direct carbonization of Co2+‐cross‐linked‐starch aerogel (Co2+‐SA) followed by low‐temperature vapor phosphorization. During successive carbonization‐phosphorization, the SA framework is formulated into 3D hierarchically porous carbon membrane matrix comprising hollow open carbon microspheres while the cross‐linked Co species are converted into uniformly distributed carbon‐encapsulated Co2P nanoparticles on carbon microspheres. Thanks to the high porosity, excellent electrolyte wettability, unique chainmail structure, and good mechanical strength, the monolithic Co2P@CSA can be directly used as a binder‐free bifunctional electrocatalyst for alkaline water splitting, and it can afford a high current density of 100 mA cm−2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at low overpotentials of 140.0 and 305.5 mV, respectively, with outstanding stability at 50 mA cm−2 for >30 h. More significantly, an alkaline electrolyzer assembled using Co2P@CSA achieves a current density of 100 mA cm−2 for overall water splitting (OWS) at a cell voltage of 1.94 V with unit Faradaic efficiency and provides a high solar‐to‐hydrogen (STH) conversion efficiency of 13.4 % when driven by a commercial silicon solar cell. This work offers an effective strategy towards cost‐effective fabrication of high‐performance carbon‐based monolithic chainmail electrocatalysts for energy conversion reactions.

Efficient rGO-supported CeO2–Y2O3–Nd2O3 nanocomposite electrocatalyst for water splitting (HER/OER) in alkaline medium

Efficient rGO-supported CeO2–Y2O3–Nd2O3 nanocomposite electrocatalyst for water splitting (HER/OER) in alkaline medium

Electrochemical deposition of nickel sulfide catalysts on commercial carbon rods as low-cost electrodes for hydrogen generation

Nowadays, the challenge of the world and the scientific community is to find and effectively use renewable energy sources. One of the renewable energy research subjects that has been hotly discussed recently is the water-splitting reaction to produce hydrogen. In this study, we focus on fabricating nickel sulfide (NiS) materials deposited on commercial carbon rod (CR) substrates and using them as electrodes for the electrochemical water-splitting reaction to produce hydrogen gas. In detail, NiS materials were decorated on commercial carbon rods (NiS/CR) by cyclic voltammetry electrochemical deposition with a potential range from 0.2 to −1.2 V (versus Ag/AgCl), a scan rate of 10 mV s−1, and 15 cycles. Benefiting a strong interfacial synergetic effect based on NiS/CR materials shows an excellent electrocatalytic activity for hydrogen evolution reaction (HER). Specifically, the NiS/CR electrode exhibits a high performance with low overpotential (70 mV for HER) and a slight Tafel slope (50 mV dec−1). Besides, annealing temperature helps increase the crystal properties, causing the appearance of NiS2 and Ni3S2 phases in NiS/CR@400 samples. Interestingly, the electrochemical surface area (ESCA) of the NiS/CR@400 sample significantly increased (17.3%) compared to the NiS/CR sample (5.8% of the total physical surface area) is due to the presence of NiS2 and Ni3S2, leading to NiS/CR@400 sample enhances the active sites by 16.0 mF cm−2. Furthermore, the long-term durability of NiS/CR@400 electrodes is good electrocatalytic over a continuous cycling 12-hour operation at 20 mA cm−2 in an alkaline environment. The NiS/CR is a promising electrode candidate for high HER performance, and here is a new design of electrocatalysts for water splitting.

Partial Exsolution Enables Superior Bifunctionality of Ir@SrIrO3 for Acidic Overall Water Splitting.

The pursuit of efficient and durable bifunctional electrocatalysts for overall water splitting in acidic media is highly desirable, albeit challenging. SrIrO3 based perovskites are electrochemically active for oxygen evolution reaction (OER), however, their inert activities toward hydrogen evolution reaction (HER) severely restrict the practical implementation in overall water splitting. Herein, an Ir@SrIrO3 heterojunction is newly developed by a partial exsolution approach, ensuring strong metal-support interaction for OER and HER. Notably, the Ir@SrIrO3-175 electrocatalyst, prepared by annealing SrIrO3 in 5% H2 atmosphere at 175 °C, delivers ultralow overpotentials of 229 mV at 10 mAcm-2 for OER and 28 mV at 10 mAcm-2 for HER, surpassing most recently reported bifunctional electrocatalysts. Moreover, the water electrolyzer using the Ir@SrIrO3-175 bifunctional electrocatalyst demonstrates the potential application prospect with high electrochemical performance and excellent durability in acidic environment. Theoretical calculations unveil that constructing Ir@SrIrO3 heterojunction regulates interfacial electronic redistribution, ultimately enabling low energy barriers for both OER and HER.

Designing core-shell heterostructure arrays based on snowflake NiCoFe-LTH shelled over W2N-WC nanowires as an advanced bi-functional electrocatalyst for boosting alkaline water/seawater electrolysis

The pursuit of efficient and sustainable hydrogen production through water splitting has led to intensive research in the field of electrocatalysis. However, the impediment posed by sluggish reaction kinetics has served as a significant barrier. This challenge has inspired the development of electrocatalysts characterized by high activity, abundance in earth's resources, and long-term stability. In addressing this obstacle, it is imperative to meticulously fine-tune the structure, morphology, and electronic state of electrocatalysts. By systematically manipulating these key parameters, the full potential of electrocatalysts can unleash, enhancing their catalytic activity and overall performance. Hence in this study, a novel heterostructure is designed, showcasing core–shell architectures achieved by covering W2N-WC nanowire arrays with tri-metallic Nickel-Cobalt-Iron layered triple hydroxide nanosheets on carbon felt support (NiCoFe-LTH/W2N-WC/CF). By integrating the different virtue such as binder free electrode design, synergistic effect between different components, core–shell structural advantages, high exposed active sites, high electrical conductivity and heterostructure design, NiCoFe-LTH/W2N-WC/CF demonstrates striking catalytic performances under alkaline conditions. The substantiation of all the mentioned advantages has been validated through electrochemical data in this study. According to these results NiCoFe-LTH/W2N-WC/CF achieves a current density of 10 mA cm−2 needs overpotential values of 101 mV for HER and 206 mV for OER, respectively. Moreover, as a bi-functional electrocatalyst for overall water splitting, a two-electrode device needs a voltage of 1.543 V and 1.569 V to reach a current density of 10 mA cm−2 for alkaline water and alkaline seawater electrolysis, respectively. Briefly, this research with attempting to combination of different factors try to present a promising stride towards advancing bi-functional catalytic activity with tailored architectures for practical green hydrogen production via electrochemical water splitting process.

Deep eutectic solvent-induced controllable synthesis of bifunctional Ni-Fe-P catalysts for electrochemical water splitting

Developing electrocatalysts with excellent activity, high stability, and low cost is vital for large-scale hydrogen production through electrochemical water splitting. Herein, a bifunctional Ni-Fe-P catalyst in situ grown on Fe foam (Ni-Fe-P/FF) is developed by a simple one-step solvothermal process in the deep eutectic solvent (DES) of ethylene glycol and choline chloride (named Ethaline). The unique solvent environment of Ethaline assisted with the regulating effect of the introduced Fe(III) ions shows an essential role in governing the preparation process. The developed Ni-Fe-P/FF acts as the efficient bifunctional electrocatalyst for water splitting in 1.0 M KOH, requiring overpotentials of 82 mV (229 mV) and 263 mV (370 mV) to deliver 10 mA cm-2 (100 mA cm-2) for oxygen and hydrogen evolution reactions, respectively. Furthermore, the self-supported catalyst-assembled electrolyzer also exhibits good catalytic performance with a low voltage of 1.83 V to drive 100 mA cm-2 and good stability over 100 h. This work offers a facile approach to fabricating high-performance bifunctional Ni-Fe-P electrocatalysts to catalyze water splitting.

Ni-tethered MoS2: In-situ fast reduction synthesis as an ultra-durable and highly active electrocatalyst for water splitting and urea oxidation

Developing an extraordinarily robust and efficient green electrocatalyst derived from earth-abundant elements is becoming an important part of green hydrogen generation. We present here a simple single-step in-situ fast reduction synthesis of Ni-tethered MoS2 (NiMoS2), which exhibits excellent activity for the Oxygen Evolution Reaction (OER), Hydrogen Evolution Reaction (HER), and Urea Oxidation Reaction (UOR). To supply 10 mA cm−2 current density, the active catalyst NiMoS2 exhibits minor overpotentials of 141 mV vs RHE (reversible hydrogen electrode) for HER, and 250 mV vs RHE for OER in 1.0 M KOH. NiMoS2 displays ultra-durability (over 90 h) with a current loss of <4.6% for OER and <3.6% for HER, respectively. The enhanced trifunctional catalyst NiMoS2/NF enables the construction of a stable behavior water electrolyzer that delivers 10 mA cm−2 at 1.52 V. With a <4.8% current loss, the NiMoS2/NF//NiMoS2/NF exhibits an ultra-stable behavior (over 150 h). The water electrolysis at 1.64 V with solar assistance demonstrates the enhanced efficacy of the synthesized catalyst. The fabricated electrode, NiMoS2 exhibits efficient catalytic activity toward the electro-oxidation of urea (UOR) (1 M KOH +0.33 M urea) at 1.39 V.

In-Site Growth of Efficient NiFeOOH/NiFe-LDH Electrodes: A Streamlined One-Step Methodology

Oxygen evolution reactions (OER) are often the decisive step in determining the water electrolysis rate. The first row of transition metals and their derivatives, represented by Ni and Fe, have attracted much attention due to their excellent OER performance. Here, we develop a one-step strategy for preparing oxygen-evolving electrodes, in which the NiFeOOH-modified NiFe layered double hydroxide (NiFe-LDH) nanosheet is supported by nickel foam. At 100 mA·cm−2, the overpotential of NiFeOOH-NiFe-LDH was just 227 mV, and the duration times were over 200 h in 1 mol·L−1 KOH. Furthermore, the co-existence of LDH and hydroxyl oxides helps the oxygen evolution reaction. These results suggest the potential for this synthesis strategy to provide a low-cost, highly active OER electrocatalyst for industrial water splitting.

Synthesis of graphene-quantum-dots decorated metal-free carbon nitride for effective electrocatalysts in redox-mediated electrolyte

Defect engineering of N/C3N4 two-dimensional material provides an efficient way to tune the electronic structures and make more active sites for electrocatalysis, which is attractive for electrochemical energy storage applications. Other than modification of heteroatoms on the top of C3N4 two-dimensional material as a photosensitizer, electrolyte design is very desirable to enrich the research area and provides a wide range of choices for diverse applications. Herein, the graphene quantum dots (GQDs) decorated N doped g-C3N4 electrocatalysts for water splitting were fabricated, which exhibited enhanced electron transfer efficiency, better electrocatalytic performance, and long-term stability. The electrochemical performances of GQDs@C3N4+x in neutral, acidic, alkaline, and redox-mediated electrolytes were investigated, respectively. The GQDs@C3N4+x electrode displays excellent activity toward electrocatalytic reaction in redox-mediated solution. The increase in electrocatalytic performance could be attributed to the reaction of redox species with the surface holes and the defects of GQDs@C3N4+x, leading to a better separation of the excited electron-hole pairs. Thus, this work greatly broadens the application prospects of carbon nitrogen complex by rational defect engineering and electrolyte regulation.

3D hierarchical porous N-doped carbon nanoarchitecture coated bimetallic phosphides as a highly efficient bifunctional electrocatalyst for overall water splitting

As the energy and ecological crises are increasingly grim, it is challengeable but extremely attractive to fabricate highly efficient and low-cost bifunctional electrocatalysts for overall water splitting (OWS). Herein, a bimetallic phosphide embedded in N-doped hierarchical porous carbon (CoP/Ni2P@NHPC) framework was successfully constructed by calcination and phosphorization of cobalt–nickel coordination polymer nanoflowers (Co/Ni CPNFs), which were obtained by a facile hydrothermal process. Benefitting from their fascinating architecture and composition, the as-prepared CoP/Ni2P@NHPC exhibits outstanding electrochemical properties for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with small Tafel slopes (103.9 mV dec-1, 62.58 mV dec-1) and ultralow overpotentials (275 mV, 159 mV at 10 mA cm−2) in alkaline medium. Additionally, the CoP/Ni2P@NHPC can be used as a bifunctional catalyst in a two-electrode water splitting device, and it only requires a low cell voltage of 1.55 V to attain the current density of 10 mA cm−2. Meanwhile, the CoP/Ni2P@NHPC also present admirable durability (at least 20 h) under long-term electrolysis. This work gives inspiration for the preparation of highly active bifunctional electrocatalysts for OWS.

Ni(OH)2/graphene nanoplatelet composite as an electrocatalyst for urea oxidation

In this work, Ni(OH)2 decorated over graphene nanoplatelets (GNP) synthesised by simple reflux reaction using hydrazine as complexing agent and sodium borohydride as reducing agent. Nickel-graphene platelet (NGP) composites are labelled as NGP-I,II and III for varying Ni-to-GNP ratios. Ni(OH)2 anchoring on GNP has been confirmed with TEM and EDS analysis. The in situ growth of Ni(OH)2 on graphene increases the stability and active sites of electrocatalysts for water splitting and direct oxidation of urea. The OER and urea oxidation on NGP-III composite were studied in 1 M KOH electrolyte, exhibiting lower potential of 1.53 V and 1.34 V vs. RHE and Tafel slope of 47 mV dec–1 and 56 mV dec–1, respectively. The negative shift in the oxidation potential of urea suggest that the urea oxidation is preferred over OER.

Ru nanoparticles decorating ferrocene-based metal-organic framework for efficient and stable water-splitting electrocatalyst

The development of stable and efficient electrocatalysts based on metal-organic frameworks represents a main challenge for the overall water splitting process. Here, the ferrocene-based nickel metal-organic framework (NiFc-MOF) on nickel foam (NF) was synthesized using nickel chloride and 1, 1′-ferrocenedicarboxylic acid (FcDA) via a simple solvothermal method, and Ru nanoparticles (NPs) were reduced by FcDA and in situ grown on the surface of NiFc-MOF nanosheets. The as-prepared cactus-like Ru0.3@NiFc-MOF exhibits high electrocatalytic activity for hydrogen evolution reaction (HER) with a low overpotential of 25 mV@10 mA cm−2 and a Tafel slope of 45.05 mV dec−1. To reach a current density of 10 mA cm−2 for the oxygen evolution reaction (OER), a low overpotential of 210 mV was required. The assembled water electrolysis cell using Ru0.3@NiFc-MOF as bifunctional electrocatalysts only requires a voltage of 1.47 V to achieve a current density of 10 mA cm−2, indicating excellent electrolytic water splitting performance. In addition, the electrocatalytic activity of Ru0.3@NiFc-MOF's can keep the stability for 120 h Ru0.3@NiFc-MOF exhibits exceptional electrocatalytic performance, which can be attributed to both the intrinsic activity of Ru sites and the multiple active sites of NiFc-MOF.

Ammonia-assisted Ni particle preferential deposition in Ni-Fe pyrophosphates on iron foam to improve the catalytic performance for overall water splitting

Designing efficient and cost-effective electrocatalysts for overall water splitting remains a major challenge in hydrogen production. Herein, ammonia was introduced to pyrophosphate chelating solution assisted Ni particles preferential plating on porous Fe substrate to form coral-like Ni/NiFe-Pyro electrode. The pyrophosphate with multiple complex sites can couple with nickel and iron ions to form an integrated network structure, which also consists of metallic nickel due to the introduction of ammonia. The large network structure in Ni/NiFe-Pyro significantly enhances the synergistic effect between nickel and iron and then improves the electrocatalytic performance. As a result, the coral-like Ni/NiFe-Pyro@IF exhibits good electrocatalytic activity and stability for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The electrolyzer assembled with Ni/NiFe-Pyro@IF as cathode and anode just needs a low water-splitting voltage of 1.54 V to obtain the current density of 10 mA cm−2. Meanwhile, the stability test of Ni/NiFe-Pyro@IF is performed at the current densities ranging from 10 to 400 mA cm−2 for 50 h without any significant decay, indicating robust catalytic stability for overall water splitting. This strategy for synthesizing metal/metal pyrophosphate composites may provide a new avenue for future studies of efficient bifunctional electrocatalysts.

Coupling NiFe-MOF with antiperovskite nickel-based nitrides as efficient electrocatalysts for overall water splitting

The exploration of high-performance, durable and cost-effective catalysts for overall water splitting, including the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), has always been a vibrant topic in electrochemical water splitting techniques. Here we report a facile strategy for the synthesis of antiperovskite bimetallic nitrides (FeNNi3 and CuNNi3) and their NiFe-MOF morphology on nickel foams (NF) for HER and OER respectively in alkaline media. The NiFe-MOF and FeNNi3 nanoparticle exhibit strong coupling and synergistic effects, resulting in a solid integrated structure and fast electron transfer. The FeNNi3 towards HER shows an overpotential of 57 mV at 10 mA cm−2 in alkaline media, and its MOF morphology shows a low overpotential of 219 mV at 10 mA cm−2 towards OER. The alkaline electrolyzer of FeNNi3/NF || NiFe-MOF@FeNNi3/NF for overall water splitting demonstrates a low cell voltage of 1.49 V at 10 mA cm−2 with high cycling durability. This work investigates antiperovskite nitrides' capabilities for overall water splitting and provides guidance on designing high-performance catalytic materials.

Rational design of MoS2@M (M=Sn, Cu, Ni, Co) hybrid nanostructures for enhanced electrocatalytic hydrogen evolution reaction

MoS2 has attracted attraction in electrocatalytic hydrogen evolution reaction (HER). The low electrical conductivity and limited exposure of active sites hindered the electrocatalytic efficiency of MoS2. In this paper, we design MoS2@M (M = Sn, Cu, Ni, Co) hybrid nanostructures by growing MoS2 nanosheets on the surface of M (M = Sn, Cu, Ni, Co) nanowires. Due to the high conductivity of metal nanowires and the increased HER active sites, the MoS2@M (M = Sn, Cu, Ni, Co) hybrid nanostructures show a superior HER efficiency. In alkaline media, the MoS2@M (M = Sn, Cu, Ni, Co) hybrid nanostructures exhibit the low overpotential of 130–172 mV at the current density of 10 mA/cm2 and a small Tafel slope of 61–86 mV/dec. In addition, the MoS2@M (M = Sn, Cu, Ni, Co) hybrid nanostructures also possess excellent electrocatalytic durability. This work provides an efficient way to achieve highly efficient MoS2 based electrocatalysts for water splitting.

Facile synthesis of Co-Cu metal organic framework as efficient non-noble bifunctional electrocatalysts for overall water splitting

The rapid development of superior, highly stable, alkaline-medium-compatible, and nonprecious earth-abundant bifunctional electrocatalysts has garnered significant research interest. This interest aims to replace the costliest noble metals (Pt, Ir/IrO2, and Ru/RuO2) in renewable and green energy technologies for overall water splitting. However, there are still important limitations, such as lower stability and higher energy consumption. In this work, we report the synthesis of Cu-Co metal-organic frameworks (MOFs) as a bifunctional electrocatalyst using a simple chemical precipitation technique. Especially, when 11.5 mM of Co is combined with Cu MOF, it exhibits excellent bifunctional activity for overall water splitting with a lower overpotential of 0.21 V (OER) and -0.71 V (HER) at a current density of 10 mA cm−2, which exhibits nearly several times more enhancement than that of pristine Cu and Co MOFs in a 1 M KOH electrolyte solution. The Tafel slope value of 130 mV/dec and the lower charge transfer resistance, along with relatively high stability for up to 12 h at the onset potential of OER and HER, are observed for the 11.5 mM Cu-Co MOF electrocatalyst. The present results open an alternative pathway for developing a novel design of highly efficient and scalable bifunctional electrocatalysts for overall water splitting.

Porous high-entropy alloy coatings as highly efficient electrocatalysts for electrocatalytic water splitting

Developing highly efficient and stable non-noble metal electrocatalysts has always been a grand challenge for water splitting. Herein, the promising and highly efficient porous high entropy alloy (HEA) coatings is fabricated through the plasma spraying, which could be favorable to solve the above issues. Abased on the synergistic effect of different metals and the porous structure within the HEA coatings, it can provide the superior catalytic activities. Hence, the CoCrFeNiMo catalyst displays a low overpotential of 273 mV (for oxygen evolution reaction, OER) at 100 mA cm−2 in 1.0 M KOH electrolyte. As hydrogen evolution reaction (HER) catalysts, the CoCrFeNiMo presents a small overpotential. When the catalysts can be utilized to the overall water splitting, it delivers an excellent durable for 24 h. DFT result shows that CoCrFeNiMo is conducive to the hydrogen adsorption/desorption process, and it can enhance the transformation of *O to *OOH and improve the OER performance. This study not only offers a universal method to prepare high performance electrocatalysts, but also demonstrates the great potential of HEA coatings in energy conversion fields.

Bifunctional Electrocatalysts for Overall and Hybrid Water Splitting.

Electrocatalytic water splitting driven by renewable electricity has been recognized as a promising approach for green hydrogen production. Different from conventional strategies in developing electrocatalysts for the two half-reactions of water splitting (e.g., the hydrogen and oxygen evolution reactions, HER and OER) separately, there has been a growing interest in designing and developing bifunctional electrocatalysts, which are able to catalyze both the HER and OER. In addition, considering the high overpotentials required for OER while limited value of the produced oxygen, there is another rapidly growing interest in exploring alternative oxidation reactions to replace OER for hybrid water splitting toward energy-efficient hydrogen generation. This Review begins with an introduction on the fundamental aspects of water splitting, followed by a thorough discussion on various physicochemical characterization techniques that are frequently employed in probing the active sites, with an emphasis on the reconstruction of bifunctional electrocatalysts during redox electrolysis. The design, synthesis, and performance of diverse bifunctional electrocatalysts based on noble metals, nonprecious metals, and metal-free nanocarbons, for overall water splitting in acidic and alkaline electrolytes, are thoroughly summarized and compared. Next, their application toward hybrid water splitting is also presented, wherein the alternative anodic reactions include sacrificing agents oxidation, pollutants oxidative degradation, and organics oxidative upgrading. Finally, a concise statement on the current challenges and future opportunities of bifunctional electrocatalysts for both overall and hybrid water splitting is presented in the hope of guiding future endeavors in the quest for energy-efficient and sustainable green hydrogen production.