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• The loading of CNT into acid-treated carbon papers enhances the 2e-transfer process. • The Faradaic efficiency for H 2 O 2 production using CNT/a-CP cathodes is ˜100. • The Faradaic efficiency for As(III) oxidation using h-TNR photoanodes is >80%. • The h-TNR and CNT/a-CP pair drives the As(III) oxidation and H 2 O 2 production. We present an off-grid, standalone electrocatalytic H 2 O 2 production reaction (HPR) using carbon nanotubes (CNT) wired to hydrogen-treated TiO 2 nanorod (h-TNR) arrays catalyzing the oxidation of As(III) to As(V) under simulated solar light (AM 1.5; 100 mW cm−2). Loading CNT onto acid-treated carbon paper (a-CP) significantly enhances the catalytic 2-electron transfer to O 2 , leading to a Faradaic efficiency (FE) of ∼100% for the HPR. To drive the HPR, the 2-electron oxidation of toxic As(III) to less toxic As(V) that accompanies the production of the proton/electron couples is achieved at an FE of >80% using the h-TNR arrays. The high FEs of the anodic and cathodic reactions are maintained over 10 h when a direct-current voltage of 0.7 V is applied to the h-TNR photoanode and CNT/a-CP cathode pair. The coupling of a mono-Si photovoltaic array that is one-tenth the size of h-TNR photoanode to the pair of h-TNR and CNT/a-CP successfully drives the standalone operation of both reactions at the high FEs (>90%). The surface characterization of the as-synthesized materials and the reaction mechanism are discussed in detail. [ABSTRACT FROM AUTHOR]

The electrochemical conversion of CO 2 into useful chemicals such as CO is a promising strategy to reduce CO 2 emissions from fossil fuel consumption and to mitigate the impacts of global warming. Although tremendous effort has been devoted to the practical use of CO 2 conversion techniques, these techniques still suffer from deficient catalytic activity toward CO 2 reduction as well as a complex catalyst synthesis procedure. In this study, an effective strategy to enhance the catalytic CO 2 reduction activity with a unique synthesis method is proposed. Polyethylene glycol (PEG)-coated Au nanoparticles supported on a porous carbon support are prepared by a facile, cost-effective, and biocompatible one-step sputtering deposition method, termed liquid medium sputtering. The use of PEG as a liquid medium is advantageous in terms of catalytic activity and stability by producing PEG layers on the Au surface. The prepared PEG-coated Au nanoparticle catalyst exhibits a CO Faradaic efficiency of 100% at −0.57 V RHE and excellent stability during 10 h of operation due to the high solubility of PEG for CO 2 . [ABSTRACT FROM AUTHOR]

Carbon blacks, which consist of the assemblies of small graphene clusters having a spherical concentric packing structure, are amorphous and have widely been used as catalyst supports for proton exchange membrane fuel cell (PEMFC) electrodes. However, poor electrochemical corrosion resistance during extended use and repeated cyclic operation of PEMFCs shortens their practical device lifetime; surface defects, such as nanosized disordered domains, have been established as the most influential factors. Herein, we coupled polymeric graphitic carbon nitride (pg-CN) with amorphous carbon black (a-CB) in a core@shell structure to produce an electrochemically efficient and stable electrocatalyst support. Our protocol allowed for the simultaneous optimization of uniformly thin graphitic shell structures for electrochemical corrosion stability and nitrogen-enriched functionalities on the carbon surfaces for electrocatalyst (e.g., platinum) nucleation. The newly prepared a-CB@pg-CNs enhanced the stable fuel cell devices operation and remained invariant even at high potential (1.2–1.7 V). Significantly, when used for constructing the PEMFC electrode, a-CB@pg-CN support-based Pt catalyst electrodes outperformed and exhibited superior stability over state-of-the-art commercial a-CB-based counterparts. Experimental observations and density functional theory (DFT) calculations revealed that the unusual electrocatalytic properties of as-prepared a-CB@pg-CNs originated from an intrinsic chemical and electronic coupling that synergistically reduced electrochemical corrosion kinetics and promoted catalyst–support interactions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A thin IrO 2 film is uniformly coated on porous Ti mesh via anodic electrodeposition. • The IrO 2 film is an efficient catalyst layer for the oxygen evolution reaction. • A high current density (0.97 A cm−2 at 1.6 V) at 0.4 mg cm−2 is produced at 120 °C. • The electrodeposited film physically blocks exposure of the Ti diffusion layer. • The IrO 2 film protects against Ti corrosion and improves cell durability at 120 °C. Abstract In this study, IrO 2 -coated Ti mesh (e-IrO 2 /Ti) is proposed to be an efficient and durable oxygen electrode for high-temperature polymer-membrane-electrolyte water electrolyzers (HT-PEMWEs). A thin IrO 2 film of submicron thickness was uniformly coated onto a porous Ti mesh substrate by anodic electrodeposition. The electrodeposited IrO 2 film plays the dual role of a catalyst layer for the oxygen evolution reaction (OER), and a corrosion-protection layer that prevents oxidation of the inner Ti. The e-IrO 2 /Ti exhibited high performance (0.97 A cm−2 at 1.6 V) despite a low IrO 2 loading (0.4 mg cm−2) in single-cell tests conducted at 120 °C, which is comparable to that of conventional electrodes with greater catalyst loadings (0.8–5 mg cm−2). Furthermore, corrosion polarization tests reveal that the IrO 2 coating physically blocks exposure of the Ti diffusion layer, thereby reducing Ti corrosion by 82% in 0.5 M H 2 SO 4 at 25 °C. The low degradation rate (1.5 mA cm‐2 h−1 (0.11% h−1)) obtained in aging experiments at 120 °C and 1.72 V (voltage efficiency of 85%) confirms the excellent stability of this electrode. [ABSTRACT FROM AUTHOR]

Chlor-alkali electrolysis is a key industrial process for the production of chlorine gas, caustic soda, and hydrogen fuels. Here, we demonstrate that a Ti foam electrode, which has a diffusion layer of liquid reactant, deposited with a thin layer of core/shell-structured mixed metal oxide nanoparticles enables almost zero polarization in the range of hundreds of mA cm−2 towards the chlorine evolution reaction (CER), using noble-metals 20 times lower than commercial electrode. The fast charge-transfer kinetics induce near-zero overpotential at low current densities, while the high mass transport rates aided by porous channels lead to unprecedentedly high CER performance (LSV derived overpotentials of 9 and 44 mV at 10 and 500 mA cm−2 with Faradaic efficiency of 99.1% and 86.1% in 5.0 M NaCl). Under practical chlor-alkali process conditions, the RNTO/Ti foam exhibited remarkable performance as a bifunctional electrode for CER and hydrogen evolution reaction (HER) with overpotential of 11 mV for HER. [Display omitted] • Core/shell-structured Ru-Ti-Nb mixed oxides exhibit superior durability at high current densities. • Liquid-diffusion electrode enables near-zero polarization for CER regardless of current density. • Exceptionally high HER activity in chlor-alkali condition with an overpotential of 11 mV at 10 mA cm−2. • Chlor-alkali electrolyzer using RNTO/Ti foams as anode and cathode exhibits 1.84 V cell voltage at 100 mA cm−2. [ABSTRACT FROM AUTHOR]

Exploiting inexhaustible free energy from the sun to produce clean and sustainable fuels is an attractive route toward the heavily polluted earth and energy shortage. Photoelectrochemical cell is strategic energy device because the generated fuels can be stored and used on-demand. Herein, we present the fabrication of Si photoelectrodes with efficient charge separation and transfer using metal-insulator-semiconductor heterostructures for energy-rich fuel production via photoelectrochemical water and urea oxidation. With controls of the native SiO x insulator layer and catalytic NiFe metal layer, Si photoelectrode exhibits a photovoltage of 530 mV and a photocurrent density of 33.3 mA cm−2 at 1.23 V versus reversible hydrogen electrode. Further employed Ni(OH) 2 catalysts allow Si photoanode to achieve fill factor of 25.73% and solar-to-hydrogen conversion efficiency of 10.8% with a perovskite/Si tandem solar cell. The fabricated Ni(OH) 2 /NiFe/n-Si photoanode shows considerable performances toward urea oxidation. Our work presents new insights into sunlight-assisted hydrogen production using wastewater. [Display omitted] • Tailored MIS photoanode based on the insulating SiOx layer, composition-controlled NiFe metal film, and Ni(OH) 2 catalyst. • Spontaneous water oxidation with STH conversion efficiency of 10.8% implemented by the PV-PEC tandem device. • Urea oxidation with a low onset potential of 0.83 V vs. RHE by the nano-heterogeneous Ni(OH) 2 /Ni 0.5 Fe 0.5 /SiO x /n-Si photoanode. [ABSTRACT FROM AUTHOR]

To reduce the use of noble metals, iridium oxide (IrO 2 ) catalysts are prepared on carbon paper (CP) by electrodeposition for use as the anodes in polymer electrolyte membrane water electrolysis (PEMWE). The activities of the fabricated electrodes toward the oxygen evolution reaction are evaluated. The loading amount and morphology of the IrO 2 deposits are varied by controlling the electrodeposition potential ( E dep ) and time ( t dep ). When electrodeposited at 0.7 V, the IrO 2 loading ranges from 0.007 to 0.464 mg cm −2 ( t dep : 1 ∼ 30 min). In the PEMWE test at 90 °C, the IrO 2 /CP electrode with an IrO 2 loading of 0.1 mg cm −2 shows the highest performance (1.92 A cm −2 at 1.8 V) in which high IrO 2 utilization is achieved without significant exposure of the substrate carbon surface. The developed IrO 2 /CP electrodes provide cell performances comparable to those in previous reports with a higher IrO 2 loading, indicating markedly enhanced mass activity. [ABSTRACT FROM AUTHOR]

A hetero-tandem organic photovoltaic (OPV) device consisting of large (PM6:IT-M) and small-bandgap (PM6:Y6) bulk-heterojunctions is developed to provide an open-circuit voltage of 1.84 V and a power-conversion-efficiency of 11.7%, which could serve as an ideal light absorber to drive water electrolysis. The fabricated OPV is combined with an electrolyzer composed of NiFeO x (OH) y and Pt electrocatalysts to demonstrate a photovoltaic-electrolysis (PV-EC) system. Furthermore, the system is designed to locate the operating voltage of the OPV-EC system at the maximum power point of OPV to minimize power loss. As a result, our hetero-tandem OPV-EC device achieves the highest solar-to-hydrogen conversion efficiency among OPV-based systems, (up to 10%), which represents a new benchmark for OPV-based solar fuel production. Finally, a wireless monolithic organic-artificial leaf is constructed for the first time, which demonstrates a stable solar hydrogen production in water. [Display omitted] • A unique hetero tandem organic photovoltaic (OPV) was fabricated consisting of two different bandgap materials. • Solar-driven water splitting system combining OPV and alkaline water electrolysis cell (EC) was fabricated. • New benchmark of STH efficiency (10%) and electricity-to-hydrogen efficiency (84.5%) were achieved. • Wireless stand-alone organic artificial leaf was implemented utilizing the same configuration. [ABSTRACT FROM AUTHOR]

In this study, we demonstrated high-rate H 2 generation by coupling with the sulfite oxidation reaction (SOR) as an alternative to the oxygen evolution reaction for solar H 2 production. The emerging and cost-effective molybdenum phosphide electrocatalyst was appropriately optimized and used as a bifunctional catalyst in an alkaline electrolyte for both SOR and HER. Powered by state-of-the-art perovskite–Si tandem photovoltaics, a remarkable photocurrent density of over 17 mA cm−2 was achieved in the HER coupled with the SOR. In addition to the significantly enhanced photocurrent, the SOR can further reduce the overall cost of solar H 2 production owing to the elimination of the expensive membranes required for H 2 and O 2 gas separation. Considering the high global demand for desulfurization via the SOR, the strategy proposed here will enable practical H 2 production from renewable sources while effectively converting the toxic SO 2 gas into a value-added product for the chemical industry. Solar hydrogen production system employing SOR as alternative anodic reaction is presented. Photoassisted electrochemical device consists of MoP-based catalysts and perovskite–Si tandem PV. Our system based on SOR demonstrates remarkable hydrogen generation photocurrent density of over 17 mA cm–2 under 1-sun illumination with prolonged durability of 50 h. [Display omitted] • Solar H 2 production employing SOR as an alternative anodic reaction is presented. • SOR enables the reduction in thermodynamic barrier for H 2 production. • Bifunctional MoP-based catalysts for SOR–HER is developed. • SOR-based PV-EC exhibits photocurrent of 17.23 mA cm–2 with durability of 50 h. [ABSTRACT FROM AUTHOR]

Ir and its oxide are the only available oxygen evolution reaction (OER) electrocatalysts with reasonably high activity and stability for commercial proton-exchange membrane electrolyzers. However, the establishment of structure–performance relationships for the design of better Ir-based electrocatalysts is hindered by their uncontrolled surface reconstruction during OER in acidic media. Herein, we monitor the structural evolution of two model Ir nanocrystals (one with a flat surface enclosed by (100) facets and the other with a concave surface containing numerous high-index planes) under acidic OER conditions. Operando X-ray absorption spectroscopy measurements reveal that the promotion of surface IrO x formation during the OER by the concave Ir surface with high-index planes results in a gradual OER activity increase, while a decrease in activity and limited oxide formation are observed for the flat Ir surface. After the activation process, the Ir concave surface exhibits ~ 10 times higher activity than the flat surface. Density functional theory computations reveal that Ir high-index surfaces are thermodynamically preferred for the adsorption of oxygen atoms and the formation of surface oxides under OER conditions. Thus, our work establishes a structure–performance relationship for Ir nanocrystals under operating conditions, providing new principles for the design of nanoscale OER electrocatalysts. Surface structure–controlled model Ir nanocrystals with flat and concave surfaces were designed as electrocatalysts for the oxygen evolution reaction under acidic conditions. The Ir concave surface containing high-index planes exhibited progressive activation during the oxygen evolution reaction due to the facile formation of active IrO x , while the flat surface showed a gradual decrease in activity. [Display omitted] • Surface structure–controlled model Ir nanocrystals with flat and concave surfaces. • The structural evolution of Ir catalysts under acidic oxygen evolution reaction. • The activation process of Ir concave surface containing high-index planes under OER. • The deactivation process of Ir flat surface during acidic OER. • The important role of high-index planes for promoting OER activity in acidic media. [ABSTRACT FROM AUTHOR]

[Display omitted] • The synergistic structure with nanoporous BiVO 4 and SnO 2 nanorods boosting the photoelectrochemical properties. • Near-complete charge separation efficiency of 97% and charge carrier dynamics of BiVO 4 /SnO 2. • Spontaneous water oxidation with STH conversion efficiency of 7.3% implemented by the PEC-PV tandem cell. As an artificial leaf, a tandem device for zero-bias solar water splitting is a capable solution for practical hydrogen production. Despite a promise, poor charge transport of BiVO 4 hampers photoelectrochemical performances under front-side illumination, which is a hindrance to the tandem system. Herein, we design a new photoanode comprising nanoporous BiVO 4 and SnO 2 nanorods focused on the charge separation via structural and interfacial engineering. BiVO 4 /SnO 2 photoanode exhibits not only remarkable charge separation efficiency of 97% but also, by loading NiFe as a co-catalyst for water oxidation, high photocurrent density of 5.61 mA cm−2 at 1.23 V versus the reversible hydrogen electrode under front-side 1 sun illumination. Consequently, a tandem cell comprising NiFe/BiVO 4 /SnO 2 photoanode and perovskite/Si tandem solar cell generates an operating photocurrent density of 5.90 mA cm−2 with a solar-to-hydrogen conversion efficiency of 7.3% in zero-bias. This work would be a significant step to develop spontaneous solar hydrogen production. [ABSTRACT FROM AUTHOR]