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Pt-supported carbon material-based electrocatalysts are formidably suffering from carbon corrosion when H2O and O2 molecules are present at high voltages in polymer electrolyte membrane fuel cells (PEMFCs). In this study, we discovered that the edge site of a fluorine-doped graphene nanoribbon (F-GNR) was slightly adsorbed with H2O and was thermodynamically unfavorable with O atoms after defining the thermodynamically stable structure of the F-GNR from DFT calculations. Based on computational predictions, the physicochemical and electrochemical properties of F-GNRs with/without Pt nanoparticles derived from a modified Hummer's method and the polyol process were investigated as support materials for electrocatalysts and additives in the cathode of a PEMFC, respectively. The Pt/F-GNR showed the lowest degradation rate in carbon corrosion and was effective in the cathode as additives, resulting from the enhanced carbon corrosion durability owing to the improved structural stability and water management. Notably, the F-GNR with highly stable carbon corrosion contributed to achieving a more durable PEMFC for long-term operation.

Seawater electrolysis is a promising technology for the production of hydrogen energy and seawater desalination. To produce hydrogen energy through seawater electrolysis, highly active electrocatalysts for the oxygen evolution reaction (OER) are required. Here, we report the development of a Ni-doped FeOOH anode for high-efficiency anion exchange membrane alkaline seawater electrolysis. The Ni-doped FeOOH anode showed an overpotential of only 301 mV in half-cell tests, reaching a current density of 100 mA cm−2 in 1.0 M KOH + seawater. An anion exchange membrane electrolyzer catalyzed by Ni-doped FeOOH exhibited a current density of 729 mA cm−2 in 1.0 M KOH + seawater with an energy conversion efficiency of 76.35%. Compared to the reported AEM electrolyzer operated in 1.0 M KOH, our AEM electrolyzer catalyzed with Ni-doped FeOOH operated in 1.0 M KOH + seawater exhibited higher performance.

Active and stable electrocatalysts are the key to water electrolysis for hydrogen production. This paper reports a facile direct growth method to synthesize NiFe-layered double hydroxides (LDHs) on nickel foil as an electrocatalyst for the oxygen evolution reaction. The NiFe-LDH is synthesized by a galvanic process at room temperature without any additional energy for synthesis. The synthesized NiFe-LDH is a karst landform with abundant active sites and efficient mass diffusion. The NiFe-LDH with an oxygen defect show excellent electrocatalytic performance for the OER, with a low overpotential (272 mV at 10 mA/cm2), a small Tafel slope (43 mV/dec), and superior durability. Direct growth synthesis provide excellent electrical conductivity as well as strong bonding between the catalyst layer and the substrate. In addition, this synthesis process is simple to apply in the fabrication of a large size electrode and is believed to be applicable to commercialized alkaline water electrolysis.

The low-temperature physical vapor deposition process of atomically thin two-dimensional transition metal dichalcogenide (2D TMD) has been gaining attention owing to the cost-effective production of diverse electrochemical catalysts for hydrogen evolution reaction (HER) applications. We, herein, propose a simple route toward the cost-effective physical vapor deposition process of 2D WSe2 layered nanofilms as HER electrochemical catalysts using RF magnetron sputtering at room temperature (

Uniquely nanostructured CuCo2O4 is presented as an electrocatalyst for oxygen evolution reactions (OER). CuCo2O4 particles in a chestnut-burr-like shape (CCO*, where ∗ = chestnut burr) were hydroth...

Co3S4 nanosheets on Ni foam (NS/NF) were prepared by sulfurization for various time after calcination of electrodeposited Co(OH)2. In our FE-SEM images, we observed that Co3S4 NS was vertically, or obliquely, deposited on the Ni foam. As a result, the structure contained more active sites, and active sites were highly accessible to the electrolyte for the hydrogen evolution reaction (HER). Furthermore, results of XPS and XRD analysis confirmed S-conversion from Co3O4 to Co3S4 during sulfurization. 3-Co3S4 NS/NF with sulfurization for 3 h exhibited the highest sulfur content, while Co3S4 began to desulfurize to Co9S8 after sulfurization for 4 h. The 3-Co3S4 NS/NF electrocatalyst showed a lowest overpotential of 93 mV at −10 mA/cm2, with a Tafel slope of −55.1 mV/dec in N2-purged 1 M KOH. Also, the single cell anion exchange membrane water electrolyzer (AEMWE) showed a high current density of 431 mA/cm2 with cell voltage 2.0 Vcell at 40–45 °C.

The application of electrocatalysts with high activity to a practical water electrolysis cell is a crucial challenge for the production of pure hydrogen and commercialization of the water electrolyzer. Herein, a nanosized Cu0.5Co2.5O4 catalyst synthesized by co-precipitation by adjusting pH is applied to the anion exchange membrane water electrolysis (AEMWE) cell as an anode, which is demonstrated to have higher efficiency and stability than noble metal-based anodes. The composition (Cu/Co) and morphology of Cu0.5Co2.5O4 change as the pH increases and then nanoparticles are formed at pH 11, where oxygen vacancies are formed by the etching of Cu. In the density functional theory study, the electronic structure of Co modified by Cu in the Co3O4 lattice leads to an optimal adsorption strength, resulting in a free energy diagram in which the potential of Cu0.5Co2.5O4 (1.756 V vs. reversible hydrogen electrode, RHE) is more thermodynamically favorable than that of Co3O4 (1.951 V vs. RHE). The Cu0.5Co2.5O4 catalyst has a recorded overpotential of 285 mV at 10 mA cm−2 in 1 M KOH. Furthermore, the AEMWE cell using Cu0.5Co2.5O4 as an anode exhibited a current density of 1.3 A cm−2 at 1.8 V, which is the highest performance among the reported papers and maintains around 80% energy conversion efficiency for 100 hours.

The selective and efficient electrocatalytic transformation of carbon dioxide (CO2) to multicarbon alcohols (e.g., C2H5OH and C3H7OH) is a challenge in renewable and sustainable energy research. Herein, a series of hybrid catalysts consisting of Cu nanoparticles supported on N-doped porous carbon (Cu/NPC) were prepared. It was demonstrated that the selectivity for C2H5OH or C3H7OH could be tuned by introducing N-doped porous carbon materials as cocatalysts with different pyridinic N contents, which could in situ produce a reactive CO intermediate from CO2. By varying the pyridinic N content, highly selective production of multicarbon alcohols was achieved using the Cu/NPC hybrid catalysts with a high faradaic efficiency for one pot production of multicarbon alcohols up to 73.3% at −1.05 V (vs. RHE). The faradaic efficiency for C2H5OH and C3H7OH was 64.6% and 8.7%, respectively. The pyridinic N species were likely the CO-producing sites and together with Cu catalytic sites acted cooperatively to produce C2H5OH and C3H7OH via a two-site mechanism for efficient CO2 reduction to multicarbon alcohols. These findings provide novel guidance for the rational design of electrocatalysts and for tuning the catalytic activity and selectivity for multicarbon alcohol production from CO2.

Recently, copper iodide (CuI) has been considered as a promising inorganic p-type semiconductor material. Although significant progress using CuI has been made in materials and device applications for solar cells and thin-film transistors (TFTs), little consideration has been given to the vacancy formation mechanisms and their effect on the device performance. In this work, high performance electrolyte-gated TFTs were fabricated using CuI semiconductors with different vacancy states and the origin of the threshold voltage (Vth) shift of devices in terms of vacancy species and concentration were studied. The CuI films were fabricated via a simple solution process followed by thermal annealing at low temperature (55 °C). The vacancy species and concentration in the CuI semiconductor were regulated by changing the annealing conditions as well as by introducing a dopant material. Photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS) analysis were conducted to demonstrate the correlation between the electrical properties of TFTs and the vacancy states in the CuI specimens. The CuI-TFTs exhibited typical enhancement mode operation of the p-channel transistor, with sub-1 V operation voltage, ON/OFF ratio of ∼103, and high hole mobility in the range of 10–60 cm2 V−1 s−1. Experimental results revealed that Cu vacancy (VCu) play the role of inducing hole carriers, hence, TFT with VCu-rich CuI exhibited increased carrier concentration and positively shifted Vth of 0.14 V. However, iodine vacancy (VI) in CuI captures hole carriers, decreasing the concentration of charge carriers (holes), resulting to a negative Vth of −0.19 V. The TFT mobility was also affected by the vacancy concentration, owing to the carrier scattering effect. For instance, the I-rich (or VCu-rich) CuI exhibited decreased TFT mobility (14.70 cm2 V−1 s−1) due to the high carrier concentration (1019 cm−3) and their scattering effect.

Single-crystalline CoFe alloy nanoparticles encapsulated in nitrogen-doped carbon nanotubes (CoFe@N–C) were synthesized through a simple heat-treatment in an N2 environment. CoFe@N–C effectively catalyzed the overall water splitting in alkaline media. Specifically, the as-synthesized CoFe@N–C exhibited excellent activity towards the oxygen evolution reaction (OER) with a low overpotential of 292 mV at 10 mA cm−2 and the hydrogen evolution reaction (HER) with a low overpotential of 110 mV at 10 mA cm−2. The good electrocatalytic properties may be attributed to the synergistic electronic coupling between single-crystalline CoFe and highly conductive N-doped CNTs and the enrichment of active sites. Additionally, CoFe@N–C showed excellent stability and durability with no observable deviation in the overpotential for the OER and HER after 1000 cycles of cyclic voltammetry (CV).

A Cu–Co–P electrocatalyst for hydrogen evolution reaction (HER) was designed with a dendritic and porous foam structure. Fabricated by one-step electrodeposition with binary alloy on a hydrogen bub...

Cobalt (Co)-incorporated MoS2 nanofibers were fabricated via a facile electrospinning method followed by sulfurization process. Co atoms in the molybdenum oxide nanofibers altered the morphology and crystal structure according to sulfurization time. The well-anchored Co-incorporated MoS2 sheets on the nanofiber surface acted as active edge sites for the hydrogen evolution reaction (HER), which exhibited high activity with an onset potential of approximately −170 mV vs NHE with a Tafel slope of 60 mV/dec. The overpotential was −330 mV vs NHE at 10 mA/cm2.

Au and Pt are well-known catalysts for electrocatalytic oxidation of biomass-derived glycerol. Although some nonprecious-metal-based materials to replace the costly Au and Pt are used for this reaction, the fundamental question of how the nonprecious catalysts affect the reaction chemistry and mechanism compared to Au and Pt catalysts is still unanswered. In this work, both experimental and computational methods are used to understand how and why the reaction performance and chemistry for the electrocatalytic glycerol oxidation reaction (EGOR) change with electrochemically-synthesized CuCo-oxide, Cu-oxide, and Co-oxide catalysts compared to conventional Au and Pt catalysts. The Au and Pt catalysts generate major glyceric acid and glycolic acid products from the EGOR. Interestingly, the prepared Cu-based oxides produce glycolic acid and formic acid with high selectivity of about 90.0%. This different reaction chemistry is related to the enhanced ability of CC bond cleavage on the Cu-based oxide materials. The density functional theory calculations demonstrate that the formic acids are mainly formed on the Cu-based oxide surfaces rather than in the process of glycolic acid formation in the free energy diagram. This study provides critical scientific insights into developing future nonprecious-based materials for electrochemical biomass conversions.

In this work, we show an effective strategy combining experimental and computational methods to explore and clarify rational design approaches utilizing transition metals for enhanced electrocatalysis of oxygen reactions. We report a bifunctional electrocatalyst synthesized by a chemical deposition of palladium (Pd) nanoparticles on three-dimensionally ordered mesoporous cobalt oxide (Pd@3DOM-Co3O4) demonstrating extreme stability and activity towards electrocatalytic oxygen reduction and evolution reactions (ORR and OER). Pd@3DOM-Co3O4 exhibits a significantly positive-shifted ORR half-wave potential of 0.88 V (vs. RHE) and a higher OER current density of 41.3 mA cm−2 measured at 2.0 V (vs. RHE) relative to non-deposited 3DOM-Co3O4. Moreover, in terms of durability, Pd@3DOM-Co3O4 demonstrates a negligible half-wave potential loss with 99.5% retention during ORR and a high current density retention of 96.4% during OER after 1000 cycles of accelerated degradation testing (ADT). Ab-initio computational simulation of the oxygen reactions reveals that the modification of the electronic structure by combining Pd and Co3O4 lowers the Pd d-band center and enhances the electron abundance at the Fermi level, resulting in improved kinetics and conductivity. Furthermore, it is elucidated that the enhanced electrochemical stability is attributed to an elevated carbon corrosion potential (Ucorr,C) for the Pd@3DOM-Co3O4 surface and an increased dissolution potential (Udiss) of Pd nanoparticles. Meanwhile, synergistic improvements in the bifunctional activity resulting from the combination of Pd and 3DOM-Co3O4 were confirmed by both electrochemical and physical characterization methods, which highlights the practical viability of Pd@3DOM-Co3O4 as an efficient bifunctional catalyst for rechargeable metal-air batteries.

Developing high-efficiency and low-cost oxygen-evolving electrodes in anion exchange membrane (AEM) water electrolysis technology is one of the major challenges. Herein, it is demonstrated that the surface corrosion of a conventional Ni foam electrode in the presence of Fe3+ and V3+ cations can transform it into an electrode with a high catalytic performance for oxygen evolution reaction (OER). The corroded electrode consists of a ternary NiFeV layered double hydroxide (LDH) nanosheet array supported on the Ni foam surface. This NiFeV LDH electrode achieves an OER current density of 100 mA cm-2 at an overpotential of 272 mV in 1 m KOH, outperforming the IrO2 catalyst by 180 mV. Density functional theory calculations reveal that the unique structure and the presence of vanadium in NiFeV LDH play a key role in achieving improved OER activity. When coupled with a commercial Pt/C cathode catalyst, the resulting AEM water electrolyzer achieves a cell current density as high as 2.1 A cm-2 at a voltage of only 1.8 Vcell in 1 m KOH, which is similar to the performance of the proton exchange membrane water electrolyzer obtained from the IrO2 and Pt/C catalysts pair.

Developing high performance, highly stable, and low-cost electrodes for the oxygen evolution reaction (OER) is challenging in water electrolysis technology. However, Ir- and Ru-based OER catalysts with high OER efficiency are difficult to commercialize as precious metal-based catalysts. Therefore, the study of OER catalysts, which are replaced by non-precious metals and have high activity and stability, are necessary. In this study, a copper–cobalt oxide nanosheet (CCO) electrode was synthesized by the electrodeposition of copper–cobalt hydroxide (CCOH) on Ni foam followed by annealing. The CCOH was annealed at various temperatures, and the structure changed to that of CCO at temperatures above 250 °C. In addition, it was observed that the nanosheets agglomerated when annealed at 300 °C. The CCO electrode annealed at 250 °C had a high surface area and efficient electron conduction pathways as a result of the direct growth on the Ni foam. Thus, the prepared CCO electrode exhibited enhanced OER activity (1.6 V at 261 mA/cm2) compared to those of CCOH (1.6 V at 144 mA/cm2), Co3O4 (1.6 V at 39 mA/cm2), and commercial IrO2 (1.6 V at 14 mA/cm2) electrodes. The optimized catalyst also showed high activity and stability under high pH conditions, demonstrating its potential as a low cost, highly efficient OER electrode material.

Pt-supported carbon material-based electrocatalysts are formidably suffering from carbon corrosion when H2O and O2 molecules are present at high voltages in PEMFC. In this study, we discovered that the edge site of a fluorine-doped graphene nanoribbon (F-GNR) was slightly adsorbed with H2O and thermodynamically unfavorable with O atoms after defining the thermodynamically stable structure of F-GNR from DFT calculations. Based on computational predictions, the physicochemical and electrochemical properties of F-GNRs with/without Pt nanoparticles derived from a modified Hummer’s method and the polyol process were investigated as support materials for electrocatalysts and additives in the cathode of a PEMFC, respectively. Pt/F-GNR showed the lowest degradation rate in carbon corrosion, and was effective in the cathode as additives, resulting from the enhanced carbon corrosion durability owing to the improved structural stability and water management. Notably, F-GNR with highly stable carbon corrosion contributed to achieving a more durable PEMFC for long-term operation.

We prepare three-dimensional honeycomb-like Cu0.81Co2.19O4 nanosheet arrays supported by Ni foam via electrochemical codeposition of cobalt and copper hydroxides on Ni foam followed by thermal oxidation. The codeposition with Cu changes the morphology of the cobalt hydroxide deposit to form honeycomb-like nanostructures, significantly decreasing the onset potential for oxygen evolution. The Cu0.81Co2.19O4 anode displays an exceptionally low overpotential of 290 mV at a current density of 10 mA cm–2 in 1 M KOH, and an anion-exchange membrane water electrolysis cell employing the above anode achieves a current density of 100 mA cm–2 at 1.68 V in 0.1 M KOH.

Indium removal and recovery on a carbon electrode under a microbial fuel cell (MFC)-based oxidation/reduction reaction were examined using synthetic wastewater. More than 90% of In3+ ions were removed after continuous operation of the MFC for 14 days with an average current generation of ∼50 μA. During operation, indium particulates formed on the cathode carbon electrode. Scanning electron microscopy equipped with X-ray energy dispersive spectroscopy showed that they were composed of amorphous and crystalline indium hydroxides (In(OH)3 and In(OH)·H2O). When the current flow was reversed to drive the oxidation of the particles to recover the indium from indium hydroxides, a few indium oxide (In2O3) nanocrystals with a rectangular platelet shape formed on the electrode, while the majority of the amorphous and crystalline indium hydroxides re-dissolved into the aqueous environment. Overall, these results demonstrate a feasible route towards the MFC-based recovery of indium with the simultaneous generation of bioelectricity.

Developing high-efficiency and cost-efficient electrodes for hydrogen and oxygen evolution reactions (HER and OER respectively) is a major challenge in water electrolysis technology. We developed a chemical transformation route that can produce both high-performance OER and HER electrodes by corrosion of a Ni foam and subsequent phosphidation process, which generated ternary NiFeCo layered double hydroxide (LDH) and phosphide nanosheets supported on the foam, respectively. Because of their compositions and high electrical conductivities, these ternary LDH and phosphide electrodes exhibited remarkably high activities for OER and HER, respectively, outperforming most of other catalysts reported to date. An alkaline water electrolyzer based on these electrodes achieved a current density of 10 mA/cm2 at an only 1.47 Vcell. In addition, anion exchange membrane water electrolyzer based on these electrodes reached a current density of 500 mA/cm2 at an only 1.75 Vcell.

Anion exchange membrane water electrolysis (AEMWE) is considered the next generation of green hydrogen production method because it uses low-cost non-noble metal oxide electrocatalyst electrodes and can store high-purity hydrogen under high pressure. However, the commercialization of AEMWE with non-precious metal oxide electrocatalysts is challenging due to low electrocatalytic activity and durability. Overcoming the low kinetics caused by four-electron transfer is vital in addressing the low activity of non-noble metal oxide electrocatalysts for oxygen evolution reaction. This article overviews the synthesis methods and related techniques for various anode electrodes applied to AEMWE systems. We highlight effective strategies that have been developed to improve the performance and durability of the non-precious electrocatalysts and ensure the stable operation of AEMWE, followed by a critical perspective to encourage the development of this technology.

Ni-based electrocatalysts for replacement of precious metal electrocatalyst, the cathode materials of anion exchange membrane water electrolyzer (AEMWE), are seriously unstable and low activity at hydrogen production conditions. This study develops a high-performance, durable non-precious metal electrocatalyst for AEMWE, which show improved activity and durability. First, Ni/C was alloyed with Co and supported on carbon cloth coated with microporous carbon layer to improve the electrocatalytic activity of the hydrogen evolution reaction (HER) electrocatalyst; then, oxide (Ni/Co-O) was locally formed on the synthesized NiCo/C to increase its activity and durability. Specifically, this oxide increased the coverage of OH− ions, formed hydrogen spillover channels, and promoted the HER. Further, its improved electrochemical durability was attributed to the high bond dissociation energy of the metal oxide. The electrocatalyst was also evaluated as the cathode in single-cell (1-cell) and stack cell (5-cell) AEMWE systems to demonstrate that this superior performance would translate to the commercial scale.

Developing high-performance and low-cost oxygen-evolving electrodes is one of major challenges in electrochemical water splitting technology. We demonstrated that the aqueous-phase corrosion of a conventional Ni foam in the presence of exotic Fe3+ cations can directly transform it into an electrode with high catalytic activity and stability for oxygen evolution reaction (OER). The surface of the corroded electrode consisted of densely packed, small Ni0.75Fe2.25O4 nanoparticles with sizes less than 5 nm. This electrode required an overpotential of only 192 mV to reach an OER current density of 10 mA/cm2 in 1 M KOH, outperforming the state-of-the-art IrO2 catalyst by 73 mV. Density functional theory calculations revealed that the unique surface structure and iron composition of Ni0.75Fe2.25O4 nanoparticles play a key role in achieving an improved OER activity. When coupled with a Pt/C hydrogen-evolving catalyst, the resulting anion-exchange membrane (AEM) water electrolyzer achieved an overall water-splitting current density as high as 2.0 A/cm2 at a cell voltage of 1.9 V in 1 M KOH, which was 1.7 times that obtained from the IrO2 and Pt/C catalyst pair and also much greater than reported values from other AEM water electrolyzers. By revisiting and exploiting a traditional corrosion process, our work opens a simple, cost-effective, and scalable route to a high-performance OER electrode for efficient AEM water electrolysis.

Hexavalent chromium wastewater is produced in electroplating processes and the heavy metal industry, highlighting the need for an environmentally friendly treatment and the recovery of chromium. This study compared the performance of microbial fuel cells implemented with a proton exchange membrane (PEM-MFC) and a bipolar membrane (BPM-MFC) using hexavalent chromium from electroplating wastewater as the catholyte. The removal of hexavalent chromium and simultaneous bioelectricity generation were enhanced significantly using a BPM. On the other hand, in the PEM-MFC, the lower pH of the electroplating wastewater (pH 1.8) in the cathodic chamber decreased the anodic pH due to proton diffusion through the PEM, and inhibited the bioelectrochemical reaction. Scanning electron microscopy showed that the reduced chromium particles precipitated on the cathode carbon electrode during the MFC operation. The precipitate was identified as amorphous chromium oxide particles by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy.

A novel electrochemical nanofilm sensor for 1-hydroxypyrene (1-OHP) was developed based on a molecular imprinted TiO2 gel matrix, which was prepared with Ti(O-n-Bu)4 and 1-OHP using sol–gel technology. Cyclic voltammetry (CV) showed that guest binding on the non-imprinted sensor resulted in nearly the same current changes for all guest molecules, indicating non-specific binding onto the TiO2 gel matrix. In contrast, binding at the molecular imprinted sensor revealed that the selectivity for 1-OHP relative to structurally related guest molecules was estimated to be 1.8–6.7 times greater at 1 × 10−9 M, reflecting its specific adsorption and binding capacity for the template molecule.

A series of binary PtRu catalysts with different Pt:Ru atomic ratios in a range from 7:3 to 3:7 are synthesized on carbon support using the colloidal method; they are then used for electrooxidation of glycerol in acidic media. X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy analyses are used to investigate the particle size, size distribution, and structural and electronic properties of the prepared catalysts. The addition of Ru content to the Pt-based catalysts caused structural and electronic modifications over the PtRu alloy catalyst formation. The electrocatalytic activities of PtRu/C series catalysts are investigated by using the cyclic voltammetry technique. Among the prepared catalysts, the Pt5Ru5/C catalyst shows enhanced catalytic activity at least 40% higher than that of the Pt/C catalyst, with improved stability for glycerol electrooxidation; these improvements can be attributed to the structural and electronic modifications of the Pt catalysts. Using an electrocatalytic batch reactor, product analysis after the oxidation reaction is performed by high-performance liquid chromatography to determine and compare the reaction pathways on the Pt/C and PtRu/C catalysts. To understand different catalytic activities of glycerol oxidation on the PtRu alloy surfaces, density functional theory (DFT) calculations have been performed and discussed with the experimental results.

The production of hydrogen from water via solar energy conversion has attracted immense attention as a potential solution for addressing energy supply issues. We demonstrated a stable and efficient organic-inorganic hybrid photoelectrochemical (H-PEC) cell. Modifying the surface energy and structure of the organic photoactive layer using multi-functional nanomaterials including –OH-modified NiO nanoparticles and reduced graphene oxide (RGO) led to a 2.8-fold enhancement of the water splitting performance in a single junction H-PEC cell. The enhanced performance was attributed to the i) improved water-wettability, ii) enhanced charge extraction property by band-edge alignment, and iii) the catalytic effect of the introduced NiO-OH nanoparticles. In addition, because of the effects of the RGO layer preventing water penetration and photo-corrosion during the oxidation of water, a distinguishable long-term stability was achieved from the H-PEC cell with an RGO capping layer. The best performance was obtained from the organic-inorganic hybrid multi-junction PEC cells consisting of the WO 3 photo-anode (activated under UV irradiation) and the H-PEC cell (activated under visible light irradiation). The H-PEC cell with a WO 3 photo-anode exhibited significantly enhanced stability and performance by a factor of 11.6 higher than photocurrent of the single H-PEC cell.