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Catalysts applied for oxygen evolution reaction (OER) are vital to bring future renewable energy systems and convert the water to oxygen and hydrogen fuel. Herein, we report that bimetal-glycerate ...

Ag2S/AgI/Ni composite films were prepared by constant current electrodeposition and characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and UV-vis diffuse reflectance spectroscopy. Under visible light (> 420 nm), Ag2S/AgI/Ni composite film photocatalyst showed higher photocatalytic (PC) activity in the degradation of rhodamine B (RhB) than a pure Ag2S/Ni film or AgI/Ni film. The composite film demonstrated excellent stability and could be recycled 11 times with an essentially unchanged PC activity. Ag nanoparticles were generated in the PC process and acted as a charge-transfer bridge, forming a [Formula: see text]-scheme composed of Ag2S, Ag, and AgI. This effectively separated the photogenerated electrons and holes, hence providing excellent PC activity and stability to the Ag2S/AgI/Ni composite film.

Manganese oxides and iron oxides have been widely introduced in constructed wetlands (CWs) for sewage treatment due to their extensiveness in nature and their ability to participate in various reactions, but their effects on greenhouse gas (GHG) emissions remain unclear. Here, a set of vertical subsurface-flow CWs (Control, Fe-VSSCWs, and Mn-VSSCWs) was established to comprehensively evaluate which are the better metal substrate materials for CWs, iron oxides or manganese oxides, through water quality and the global warming potential (GWP) of nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2). The results revealed that the removal efficiencies of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) in Mn-VSSCWs were all higher than that in Fe-VSSCWs, and manganese oxides could almost completely suppress the CH4 production and reduce GWP (from 8.15 CO2-eq/m2/h to 7.17 mg CO2-eq/m2/h), however, iron oxides promoted GWP (from 8.15 CO2-eq/m2/h to 10.84 mg CO2-eq/m2/h), so manganese oxides are the better CW substrate materials to achieve effective sewage treatment while reducing the greenhouse gas effect.

In this work, a dynamic self-optimizing material consisting of nickel–sulfide nanosheets anchored onto Ni foam (DSO-Ni3S2-NF) as the model material was constructed using a hydrothermal method, and its electrocatalytic performance for oxygen evolution was evaluated. It was found that the electrocatalytic activity of the dynamic self-optimizing (DSO) 25 h-Ni3S2-NF for oxygen evolution is significantly enhanced compared with that of pristine 0 h-Ni3S2-NF since the formed oxide layer evolves into new active sites and the specific process of activity optimization was explored dynamically. The best oxygen evolution reaction (OER) performance was achieved by 25 h-Ni3S2-NF catalyst, which required merely 241 mV overpotential to deliver a current density of 20 mA cm−2, and its Tafel slope was as low as ∼40 mV dec−1, which was superior to most nickel-based catalysts, in 1 M KOH electrolyte. The current density was found to be increased gradually at the same potential and the stability test curves were steady with ignorable decline, showing that the promising strategy of the preparation of a dynamic self-optimizing pre-catalyst may open a new pathway to prepare low-cost, high-performance and stable water splitting catalysts.

Nitrate and sulfate are crucial factors of eutrophication and black and odorous water in the surface water and thus have raised increasing environmental concerns. Constructed wetlands (CWs) are the last ecological barrier before effluent enters the natural water body. To explore the simultaneous removal of nitrate and sulfate, the CW microcosms of CW-Con (with quartz sand), CW-ZVI (quartz sand and zero-valent iron), CW-Mag (quartz sand and magnetite), CW-ZVI + Mag (quartz sand, ZVI and magnetite) groups were set up under the low (100 mg/L)/high (300 mg/L) chemical oxygen demand (COD) concentration. Under the high COD condition, CW-ZVI group showed the best performance in nitrate (97.1%) and sulfate (96.9%) removal. Under the low COD concentration, the removal content of nitrate and sulfate in CW-ZVI group was better than CW-Mag group. The reason for this result was that zero-valent iron (ZVI) could be the electron donor for nitrate and sulfate reduction. Meanwhile, ZVI promoted chemical denitrification under high COD concentration according to PCA analysis. In addition, the produced sulfides inhibited the relative abundance of denitrifying bacteria, resulting in the lowest nitrate removal rate in CW-Mag group with sufficient electron donors. This study provided an alternative method to enhance simultaneous sulfate and nitrate removal in CWs.

Iron oxides and dissimilated metal-reducing bacteria (DMRB) have been reported to result in a reduction in methane (CH

Inexpensive and highly efficient bifunctional electrocatalysts are vital for water splitting. Herein, free-standing heterogeneous MoS2/NiCoS nanosheets as a bifunctional electrocatalyst for overall water splitting are designed. The abundant heterogeneous interfaces in MoS2/NiCoS, enriched holes and few-layer structure of MoS2 can not only provide enriched active sites but also accelerate electron/ion transfer. Consequently, the optimized MoS2/NiCoS heterostructure achieves a low overpotential of 189 mV for the hydrogen evolution reaction (HER) and 290 mV for the oxygen evolution reaction (OER) at 10 mA cm−2 in an alkaline electrolyte. In particular, in a two-electrode electrolyzer assembly, the MoS2/NiCoS heterostructure nanosheets can afford a current density of 10 mA cm−2 at a voltage of 1.50 V, serving as one of the best water-splitting electrocatalysts to date. This work provides a feasible strategy to construct efficient free-standing heterogeneous bifunctional electrocatalysts for overall water splitting.

Pt-Based alloys enclosed with high-index facets (HIFs) generally show much higher specific catalytic activities than their counterparts with low-index facets in electro-catalytic reactions. However, the exposure of a certain Pt surface would require a well-defined nanostructure, which usually can only be obtained at larger sizes. Therefore, a low dispersion of Pt atoms in Pt-based alloys with HIFs would affect the atomic utilization of Pt, resulting in most of these Pt-based alloys exhibiting lower mass activity than commercial Pt/C and Pt black catalysts for electro-catalytic reactions. Herein, we address a novel strategy to divide the surface areas of larger sized nanocrystals into small surface area nanocrystals by in situ etching Pt-Fe-Mn concave cubes (CNCs) while maintaining the morphology of the Pt-Fe-Mn alloys to improve the utilization of Pt atoms and thus increase the mass activity. Remarkably, the Pt-Fe-Mn unique concave cube (UCNC) nanocrystals (NCs) showed much higher specific and mass activities toward the methanol oxidation reaction (MOR) than the Pt-Fe-Mn CNCs, commercial Pt black and Pt/C. The kinetic analysis from Tafel plots indicated that UCNC Pt-Fe-Mn NCs had the lowest Tafel slope at whole potentials and the splitting of the first C-H bond of a CH3OH molecule with the first electron transfer was the rate-determining step at high potentials (above 0.45 V). In situ Fourier transform infrared reflection (FTIR) spectroscopic investigation at the molecular level indicated that methanol chemical absorption took place at a low potential of -0.2 V at the UCNC NC electrode. Meanwhile, much higher CO2 productivity was observed at the UCNC NC electrode, indicating the strong anti-poisoning ability of the UCNC Pt-Fe-Mn NCs during methanol electrooxidation. Furthermore, in the formic acid oxidation (FAOR) test, the activity and long-term durability of the Pt-Fe-Mn UCNC NCs were also found to be superior to those of the Pt-Fe-Mn CNCs, commercial Pt black and Pt/C. The enhanced catalytic performance in both the MOR and FAOR is most probably due to the unique HIF structure consisting of small sized particles, enhanced Pt utilization, the richness of crystalline defects and synergetic effects of Pt, Fe, and Mn metals. Our present work provides an insight into the rational design of Pt based alloys with HIFs to improve the catalytic performance of electro-catalytic reactions for fundamental study.

Ni/Fe-based bimetallic nanoarchitecture materials play an important role in the development of non-precious-metal-based electrocatalysts toward water splitting, but the low activity and poor stabil...

The instable structure of Pt-based high-indexed facets (HIFs) facile reconstructed is a key obstacle for further practical applications because of its high surface energy and amounts of undercoordinated surface atoms. Herein, a strategy to advance the fundamental surface study on Pt-based HIFs materials is addressed by implanting non-noble metal or nonmetals as “active auxiliaries” into the near-surface of noble metal nanocrystals bounded with HIFs to engineer a stable structured catalyst. Then the Mo/Pt3Mn catalysts serving as proof-of-concept examples are designed and show enhanced catalytic performance of ethylene glycol (EG). According to the electrochemical in situ Fourier transform infrared spectroscopy results, the Mo modified Pt3Mn alloys with HIFs promote not only the C–C cleavage of EG but also the direct conversion of COHX to CO2, without the formation of COL poison species. In this case, the Mo/Pt3Mn catalysts show the greatly significant increase of the catalytic activity in copamprison with ...

In this work, a dynamic self-optimizing material consisting of nickel-sulfide nanosheets anchored onto Ni foam (DSO-Ni

Iron oxides and dissimilated metal-reducing bacteria (DMRB) have been reported to result in a reduction in methane (CH4) emissions in constructed wetlands (CWs), but their mechanisms on CH4 production and oxidation remains unclear. Here, a set of CW matrix systems (Control, Fe-CWs, and FeB-CWs) was established to analyze the CH4 emission reduction from various angles, including the valencies of iron, microbial community structure and enzyme activity. The results revealed that the addition of iron oxides promoted the electron transfer between methanogens and Geobacter to promote CH4 production, but it was interesting that iron oxides also reduced the enzymes involved in the carbon dioxide (CO2) reduction pathway and promoted the enzymes that participated in anaerobic oxidation of methane (AOM) thereby leading to the overall reduction in CH4 emissions. Moreover, DMRB could promote iron reduction thereby further reducing CH4 emissions by promoting AOM and competing with methanogens for organic substrates.

Considering the practical use of electrochemical water splitting, it is important to construct a highly efficient and stable hydrogen evolution reaction (HER) electrocatalyst over a wide pH range. Herein, we develop an efficient strategy to enhance the electrochemical activity of few-layer MoS2 and Pt nanoparticles (NPs) anchored on multi-wall carbon nanotube (MWCNTs). The as-prepared Pt-MoS2/MWCNTs provides an excellent HER electrocatalytic activity with low overpotentials at −10 mA cm−2 over a wide pH range, namely, 20 mV in 0.5 M H2SO4, 92 mV in 1.0 M phosphate buffer solution (PBS), and 75 mV in 1.0 M KOH, respectively. In addition, Pt-MoS2/MWCNTs deliver the highest mass activity at the overpotential of 0.05 V, which is 8.1, 2.3, and 26.5 times higher than that of commercial 20 wt% Pt/C in acidic, neutral and alkaline media, respectively. Density functional theory (DFT) calculations revealed that the co-existence of MoS2 and Pt NPs facilitated the water dissociation reaction and hydrogen generation, thereby enhancing the activity of HER. This work provides a potential strategy to construct high-performance electrocatalysts for HER over the entire pH range.

In recent years, two-dimensional (2D) Ni-based bimetallic sulfides have been widely studied for oxygen evolution reaction (OER). However, traditional 2D nanomaterials are easily re-stacked into dense structures or films when manufactured into practical electrodes. Herein, we report an efficient approach to construct amorphous holey NiMS nanosheets (M = Co, Fe, Mn) to overcome this difficulty. Taking amorphous holey NiCoS nanosheets (denoted as holey NiCoS-NS) as a model material, we illustrate the feasibility of this method to control the hole size and pore density in the nanosheets by altering the time of sulfidation process. Benefiting from porous 2D architecture, S-doped species, synergistic effects of Ni and Co, as well as amorphous nature, the holey NiCoS-NS exhibit a low overpotential of 280 mV at current density of 10 mA cm−2 and excellent stability in 1.0 M KOH. By the X-ray photoelectron spectrum (XPS) analysis, this enhanced performance is ascribe to the in-situ generated Ni/Co oxy(hydroxide) active phase during oxygen evolution reaction. Besides, when further employed as a two-electrode electrolyzer assembly, the holey NiCoS-NS exhibits a low potential of 1.58 V at 20 mA cm−2, serving as one of the best water-splitting electrocatalysts to date. This work not only provides a feasible strategy to develop efficient and durable OER catalysts but also represents a general strategy for the structure-performance relationship of 2D transition metal sulfide electrocatalysts.