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The application of metal-organic frameworks (MOFs) as electrocatalysts for small molecule activation has been an emerging topic of research. Previous studies have suggested that two-dimensional (2D) dithiolene-based MOFs are among the most active for the hydrogen evolution reaction (HER). Here, a three-dimensional (3D) dithiolene-based MOF, Cu[Ni(2,3-pyrazinedithiolate)2] (1), is evaluated as an electrocatalyst for the HER. In pH 1.3 aqueous electrolyte solution, 1 exhibits a catalytic onset at -0.43 V vs the reversible hydrogen electrode (RHE), an overpotential (η10 mA/cm2) of 0.53 V to reach a current density of 10 mA/cm2, and a Tafel slope of 69.0 mV/dec. Interestingly, under controlled potential electrolysis, 1 undergoes an activation process that results in a more active catalyst with a 200 mV reduction in the catalytic onset and η10 mA/cm2. It is proposed that the activation process is a result of the cleavage of Cu-N bonds in the presence of protons and electrons. This hypothesis is supported by various experimental studies and density functional theory calculations.

Noble metal-free and highly efficient electrocatalytic materials with hierarchically porous structures continue to be studied for the oxygen reduction reaction (ORR) in microbial fuel cells (MFCs). We report bimetal-organic framework (bi-MOF)-derived nanocubic Swiss cheese-like carbons with a novel three-dimensional hierarchically porous structure (3D Co-N-C) prepared by utilizing cetyltrimethyl-ammonium bromide (CTAB) as a structure-directing agent to control the formation of a nanocubic skeleton, and silica spheres as a template to form a mesoporous structure. The elemental composition and chemical morphology of this material can be tuned through the Zn/Co ratio to optimize its ORR catalytic activity. The optimized 3D Co-N-C displays excellent ORR catalytic performance (half-wave potential as high as 0.754 V vs . reversible hydrogen electrode and diffusion-limiting current density of 5.576 mA cm−2) in 0.01 mol L−1 phosphate-buffered saline (PBS electrolyte), showing it can compete with the commercial 20 wt% Pt/C catalysts. The catalytic capability and long-term durability of 3D Co-N-C as an air-filled cathode electrocatalyst in an MFC device are tested, showing that the 3D CoNC-MFC can reach a high power density of 1257 mW m−2 and provide a competitive voltage during a periodic feeding operation for 192 h; these values are much higher than those of the Pt/C-MFC.

Designing reasonable MOFs-derived carbon materials to further effectively improve the catalytic activity toward ORR in the practical application of fuel cells is very necessary but remains a great challenge. Herein, a new facile yet robust strategy, self-sacrifice template approach combined with a variety of MOFs, to achieve core–shell ZnO@zeolitic imidazolate frameworks precursor (ZnO@ZIF-8@ZIF-67) is developed. Subsequently, the porous hybrid hollow carbon shell (Zn/Co-NC) can be obtained by calcinating the precursor. Impressively, the Zn/Co-NC-800 prepared by pyrolysis at 800 °C manifests excellent ORR performances with a positive onset potential of 1.03 V (vs. reversible hydrogen electrode) (vs. RHE), a more positive half-wave potential at 0.856 V (vs. RHE, a positive shift of 28 mV compared with the Pt/C) and 4-electron pathway (n = 3.80). Also, it performs higher long-term stability (only a 7.9% decay of initial current density after 20000 s) and better methanol tolerance in comparison with the traditional Pt/C in alkaline media. In our current work, the synthesis strategy of the self-sacrificing template combined with ZIFs opens up a new route for the preparation of highly efficient non-precious metal electrocatalysts for ORR.

Designing low-cost, easy-fabricated, highly stable and active electrocatalysts for oxygen evolution reaction (OER) is crucial for electrochemical (EC) and solar-driven photoelectrochemical (PEC) water splitting. By using a facile heating-electrodeposition method, here we fabricated a porous but crystalline Fe-doped Ni3S2. A thin porous surface NiFe hydroxide layer (~10 nm) is then formed through OER-running. By virtue of the core Fe-doped Ni3S2 with good conductivity and the shell NiFe hydroxide surface with good electrocatalytic activity, the core–shell nanostructure on Ni foam exhibits excellent OER activity in 1 M NaOH, needing only 195 and 230 mV to deliver 10 and 100 mA/cm2, respectively, much more superior to those of 216 and 259 mV for the sample deposited under normal temperature. The enhanced photo-response of the sulfide@hydroxide core–shell structure was also demonstrated, due to the efficient transfer of photo-generated carriers on the core/shell interface. More interestingly, it shows a good compatibility with Si based photoanode, which exhibits an excellent PEC performance with an onset potential of 0.86 V vs. reversible hydrogen electrode, an applied bias photon-to-current efficiency of 5.5% and a durability for over 120 h under AM 1.5 G 1 sun illumination, outperforming the state-of-the-art Si based photoanodes.

Ammonia (NH3) offers extensive applications in industrial production; moreover, it is a potential carrier for hydrogen energy and an eco-friendly fuel. Electrocatalytic synthesis of NH3 has drawn increasing research attention, wherein an excellent electrocatalyst plays a vital role. Iron (Fe) oxide nanomaterials with their high activity and cost effectiveness of its raw material Fe, have received significant attention in electrocatalytic N2 reduction reaction (NRR) to synthesize NH3. This study reports a rapid and cost-effective electrochemical method for synthesizing magnetic Fe3O4 nanoparticles, achieving gram-level production under ambient conditions. The synthesized magnetic Fe3O4 nanoparticles as electrocatalyst for NRR, achieved excellent faradaic efficiency of 16.9% and an optimal NH3 yield of 12.09 μg h−1 mg−1cat. at −0.15 V (versus the reversible hydrogen electrode (RHE)) in 0.1 M Na2SO4. Besides, density functional theory (DFT) calculations indicate that the N≡N bond was fully activated, and the NRR proceeds mainly along the alternating hydrogenation pathway.

Reversible hydrogen absorption/desorption, the very fundamental property of metal hydrides (MHs), can be utilized to innovate the water splitting process. Spontaneous hydrogen absorption by a MH electrode shifts the water reduction potential to 0.3 V above the reversible hydrogen electrode. Then, the absorbed hydrogen can be released to give H2 by thermal dehydrogenation at mild temperature below 70 °C by utilizing low grade heat. The MH mediated water splitting combines the electrochemical hydrogen absorption in Ni-MH batteries and the thermal dehydrogenation in gas phase hydrogen storage, which significantly reduces the electrical energy consumption for water splitting up to 25 kJ (mol H2)−1 compared to an ideal hydrogen evolution catalyst and also automatically leads to decoupled H2/O2 generation. The advantages and mechanisms of the MH mediated water splitting are demonstrated by MH electrodes with surface Pd coating.

Studying the oxygen reduction reaction (ORR) in the alkaline electrolyte has proven to promote better catalytic responses and accessibility to commercialization. Ni-nanowires (NWs) were synthesized via the solvothermal method and modified with Pt using the spontaneous galvanic displacement method to obtain PtNi-NWs. Carbon Vulcan XC-72R (V) was used as the catalyst support, and they were doped with NH3 to obtain PtNi-NWs/V and PtNi-NWs/V-NH3. Their electrocatalytic response for the ORR was tested and PtNi-NWs/V provided the highest specific activity with logarithmic values of 0.707 and 1.01 (mA/cm2Pt) at 0.90 and 0.85 V versus reversible hydrogen electrode (RHE), respectively. PtNi-NWs showed the highest half-wave potential (E1/2 = 0.89 V) at 1600 rpm and 12 μgPt/cm2 in 0.1 M KOH at 25.00 ± 0.01 °C. Additionally, the catalysts followed a four-electron pathway according to the Koutecký-Levich analysis. Moreover, durability experiments demonstrated that the PtNi-NW/V performance loss was like that of commercial Pt/V along 10,000 cycles. Electrochemical ORR in situ X-ray absorption spectroscopy results showed that the Pt L3 edge white line in the PtNi-NW catalysts changed while the electrochemical potential was lowered to negatives values, from 1.0 to 0.3 V versus RHE. The Pt/O region in the in situ Fourier transforms remained the same as the potentials were applied, suggesting an alloy formation between Pt and Ni, and Pt/Pt contracted in the presence of Ni. These results provide a better understanding of PtNi-NWs in alkaline electrolytes, suggesting that they are active catalysts for ORR and can be tuned for fuel cell studies.

Design and engineering of low-cost, high-performance catalysts is a critical step in electrochemical CO2 reduction (CO2R) to value-added chemicals and fuels. Herein, SnO2 nanoparticles were grown onto carbon cloth (SnO2/CF) by a facile hydrothermal procedure and exhibited excellent electrocatalytic activity towards CO2R due to reconstruction into SnO2/Sn Mott-Schottky heterojunctions during CO2R electrolysis, as manifested in X-ray diffraction, X-ray photoelectron spectroscopy, and operando Raman spectroscopy measurements. The heterostructured SnO2/Sn electrode delivered a high faradaic efficiency of 93 ± 1% and a partial current density of 28.7 mA cm−2 for formate production at − 1.0 V vs. reversible hydrogen electrode in an H-type cell (which remained stable for 9 h), and 174.86 mA cm−2 at − 1.18 V on a gas-diffusion electrode in a flow cell. Density functional theory calculations show that the SnO2/Sn heterostructures in situ formed under CO2R conditions helped decrease the energy barrier to form formate as compared to pristine SnO2 and Sn, and were responsible for the high activity and selectivity of formate production. Results from this study unravels the evolution dynamics of SnO2 catalysts under CO2R condition and provides a further understanding of the active component of SnO2 catalyst in CO2R.

Hybrid catalysts composed of transition metals and nitrogen-doped carbons have been emerging as one of efficient electrocatalysts for electrochemical CO2-to-CO under ambient conditions. Herein, NiO loaded on mesoporous graphene with tunable concentration of pyridinic nitrogen is rationally synthesized by using low-intensity pulsed laser irradiation and pyrolysis treatments. Comprehensive experiments verify that, it is pyridinic N, rather than pyrrolic N, when bonded to Ni, that significantly enhance the electrochemical CO2 reduction reaction performance. The optimized catalyst exhibits a high CO Faradaic efficiency of 87.5% at a low potential of −0.74 V vs. reversible hydrogen electrode, associated with negligible attenuation of continuous operation over 12 h.

Hybrid electrode materials composed of metal-organic framework (MOF)-derived oxides and conducting polymers have abundant potential for energy applications. The energy storage and conversion phenomena of such materials are due to their high porosity, long stability, good conductivity, low charge transport resistance, and fast charge-discharge rate. Herein, CuxO-C/PANI is synthesized by the in situ polymerization of aniline on multilayered mesoporous CuxO-C from Cu-MOF. Such an integrated hybrid can provide a potential route for electron transfer and improve the kinetics of redox reactions. Subsequently, the CuxO-C/PANI composite demonstrates a maximum specific capacitance of 1308 F g−1 at 1 A g−1 in a 3-electrode system. Additionally, as a fabricated device, CuxO-C/PANI//ZIF-8NPC shows an uppermost energy density of 55.1 W h kg−1 (at a 862.4 W kg−1 power density) and power density of 8668.2 W kg−1 (at a 30.1 W h kg−1 energy density), with 88.3% capacitance retention, even after 10000 cycles. Additionally, CuxO-C/PANI, as an efficient oxygen reduction catalyst, delivers an outstanding onset potential (0.94 V) and half-wave potential (0.76 V) against the reversible hydrogen electrode with good stability. Hence, these results show that the as-fabricated electrode material is an efficient alternative electrocatalyst for energy storage and oxygen reduction applications.

Hematite (α-Fe2O3) is a promising photoanode for photoelectrochemical (PEC) water splitting. However, the severe charge recombination and sluggish water oxidation kinetics extremely limit its use in photo-hydrogen conversion. Herein, a co-activation strategy is proposed, namely through phosphorus (P) doping and the loading of CoAl-layered double hydroxides (CoAl-LDHs) cocatalysts. Unexpectedly, the integrated system, CoAl-LDHs/P-Fe2O3 photoanode, exhibits an outstanding photocurrent density of 1.56 mA/cm2 at 1.23 V (vs. reversible hydrogen electrode, RHE), under AM 1.5 G, which is 2.6 times of pure α-Fe2O3. Systematic studies reveal that the remarkable PEC performance is attributed to accelerated surface OER kinetics and enhanced carrier separation efficiency. This work provides a feasible strategy to enhance the PEC performance of hematite photoanodes.

Poplar pretreated by steam explosion was used as an adsorbent to simulate the adsorption process of nickel ion in wastewater. The result of kinetics suggested that the pseudo-second-order model was well suited to describing the adsorption of nickel ion. Through controlled adsorption, steam-exploded poplar was recycled after Ni2+ adsorption and then reduced to carbon-supported nickel catalyst (NiC700). Spectrum analyses of Fourier transform infrared spectrometry (FTIR), X-ray diffractometry (XRD), X-ray photoelectron spectrometry (XPS), Brunauer Emmett-Teller (BET) surface area, and electrochemical tests were applied to study the properties of the NiC700 relative to the control carbonized materials having no Ni (C700). The FTIR analysis revealed that there were chemical interactions and ion changes between OH, C–H, C=O, and heavy metal ions in the bio-adsorption process of nickel. The surface area of NiC700 was 1480 m2/g. The presence of Ni nanoparticles in NiC700 after reduction was confirmed by the XRD and XPS analyses. Electrochemical impedance spectroscopy (EIS), photocurrent (IT), and Mott Schottky curve results revealed that the conduction band potential of NiC700 (ECB, NiC700) was -0.10 eV vs. RHE (reversible hydrogen electrode) as an n-type semiconductor, and the Ni-doped carbon fiber exhibited certain electrophotocatalytic activity due to the nickel modification.

Electrocatalytic reduction of carbon dioxide (CO2) into value-added products (e.g., ethylene) is a promising approach for greenhouse gas mitigation, but many details of electrocatalytic CO2 reduction reactions (CO2RR) remain elusive. Raman spectroscopy is suitable for in situ characterization of CO2RR mechanisms, but the low signal intensity and resulting poor time resolution (often up to minutes) hampers the application of conventional Raman spectroscopy for the study of the dynamic CO2 reduction reaction, which requires sub-second time resolution. By using Time-Resolved Surface Enhanced Raman Spectroscopy (TR-SERS) we were able to successfully monitor CO2RR over Cu surfaces with sub-second time resolution. Anodic treatment at 1.55 V vs. the reversible hydrogen electrode (RHE) and subsequent surface oxide reduction (below -0.4 V vs. RHE) induced roughening of the Cu electrode surface, which resulted in hot-spots for TR-SERS, enhanced time resolution (down to ~ 0.7 s) and improved CO2RR efficiency (i.e., four-fold increase in ethylene faradaic efficiency). With TR-SERS, the initial formation of hot-spots for SERS and CO2RR was followed (

Cu-based electrocatalysts can effectively facilitate carbon dioxide electrochemical reduction (CO2ER) to produce multi-carbon products. However, the roles of Cu0 and Cu+ and the mechanistic understanding remain elusive. This paper describes the controllable construction of Cu0-Cu+ sites derived from the well-dispersed cupric oxide supported on copper phyllosilicate lamella to enhance CO2ER performance. Specifically, 20% Cu/CuSiO3 shows the superior CO2ER performance with 51.8% C2H4 Faraday efficiency at -1.1 V vs reversible hydrogen electrode (RHE) during the 6 hours-test. In situ attenuated total reflection infrared spectra and density functional theory calculations were employed to elucidate the reaction mechanism over Cu0-Cu+ sites. The enhancement in CO2ER activity is mainly attributed to the synergistic effect of Cu0-Cu+ pairs: The Cu0 site activates CO2 and facilitates the following electron transfers; while the Cu+ site strengthens the *CO adsorption to further boost C-C coupling. This paper provides an efficient strategy to rationally design Cu-based catalysts with viable valence states to boost CO2ER.

Industrial-scale ammonia (NH3) production mainly relies on the energy-intensive and environmentally unfriendly Haber-Bosch process. Such issue can be avoided by electrocatalytic N2 reduction which however suffers from limited current efficiency and NH3 yield. Herein, we demonstrate ambient NH3 production via electrochemical nitrite (NO2−) reduction catalyzed by a CoP nanoarray on titanium mesh (CoP NA/TM). When tested in 0.1 M PBS (pH = 7) containing 500 ppm NO2−, such CoP NA/TM is capable of affording a large NH3 yield of 2,260.7 ± 51.5 µg·h−1·cm−2 and a high Faradaic efficiency of 90.0 ± 2.3% at −0.2 V vs. a reversible hydrogen electrode. Density functional theory calculations reveal that the potential-determining step for NO2− reduction over CoP (112) is *NO2 → *NO2H.

The typical Haber technical process for industrial NH3 production involves plenty of energy-consumption and large quantities of greenhouse gas emission. In contrast, electrochemical N2 reduction proffers environment-friendly and energy-efficient avenues to synthesize NH3 at mild conditions but demands efficient electrocatalysts for the N2 reduction reaction (NRR). Herein we report for the first time that commercial indium-tin oxide glass (ITO/G) can be used as a catalyst electrode toward artificial N2 fixation, as it demonstrates excellent selectivity at mild conditions. Such ITO/G delivers excellent NRR performance with a NH3 yield of 1.06 × 10−10 mol s−1 cm−2 and a faradaic efficiency of 6.17% at –0.40 V versus the reversible hydrogen electrode (RHE) in 0.5 M LiClO4. Furthermore, the ITO/G also possesses good electrochemical stability and durability. Finally, the possible reaction mechanism for the NRR on the ITO catalysts was explored using first-principles calculations.

Active and durable oxygen reduction reaction (ORR) catalysts are of utmost importance to realize the commercialization of hydrogen fuel cells and metal-air batteries. Al-substituted MnFe2O4-based ternary oxide and reduced graphene oxide (MAF-RGO) nanocomposite is synthesized using an in-situ co-precipitation followed by a hydrothermal process and verified for ORR electrocatalysis in the alkaline electrolyte (0.1 M KOH). MAF-RGO is first analyzed using physicochemical characterization tools including X-ray diffraction, Raman spectroscopy, sorption studies, electron microscopy, X-ray photoelectron spectroscopy, etc. Further, the characteristic ORR peak centered at 0.56 V vs. reversible hydrogen electrode (RHE) in cyclic voltammetry (CV) studies confirms the electrocatalytic performance of MAF-RGO. The ORR onset potential of 0.92 V vs. RHE is obtained in linear sweep voltammetry (LSV) measurement at 1600 rpm in O2-saturated electrolyte exhibiting an improved ORR performance as compared to the commercial electrocatalyst. The reduction kinetics is observed to follow the desirable near 4-e- mechanism. In addition, the electrocatalyst exhibits improved relative current stability of 86% and methanol poisoning resistance of 82%, which is better in comparison to the standard Pt/C. The observed electrochemical performance results from the synergism between the oxygen vacancy-rich Al-substituted metallic oxide active species and the functional group enriched predominantly mesoporous RGO sheets with excellent electrical conductivity. The introduction of metallic species enhanced the inter-planar spacing between graphitic sheets easing the maneuver of reactant species through the electrocatalyst and accessing more ORR-active sites. This study establishes the potency of mixed transition metal oxide/nanocarbon composites as durable high-performance ORR-active systems.

The impact of interfacial electric fields on electrochemical reaction kinetics is assessed in the context of hydrogen electrocatalysis. Recent efforts have proposed that interfacial electric field strength, as described by the electrode’s potential of zero free charge (pzfc), contributes to the slow kinetics of the alkaline hydrogen evolution and oxidation reactions (HER/HOR) by hindering solvent reorganization. In this work, we examine through single-crystal voltammetry the importance of the interfacial electric field strength on hydrogen reaction kinetics using three complementary approaches: (1) correlating the pzfc with reaction kinetics using caffeinated Pt as a model surface; (2) varying the electrolyte ionic strength at constant pH; and (3) probing solvent dynamics via caffeinated kinetic isotope effects (KIEs). Our results show that pzfc seems to correlate with HER/HOR kinetics, but also suggest that the effect more likely originates from activation barriers to the reaction elementary steps than from electric field effects on solvent dynamics. Although the importance of interfacial phenomena such as the electrode’s pzfc and water reorganization energy are well established, the pzfc may not be a mechanistic descriptor of the alkaline hydrogen reaction kinetics. Surface additives such as caffeine may help elucidate the origin behind the slow alkaline HER/HOR kinetics and ways to manipulate it.

Herein, the application of a N-doped graphitic-carbon-coated iron nitride composite dispersed in a N-doped carbon framework (Fe3N@NG/NC) is investigated as a heterogeneous electro-Fenton (HE-EF) catalyst for the efficient removal of organics. The simultaneous carbonization and ammonia etching of iron-based metal organic framework (Fe-MOF) materials yielded well-dispersed N-doped carbon-coated Fe3N nanoparticles with a diameter of ~70 nm. The Fe3N and pyridinic N endowed the composite with high HE-EF activity for decomposing the electrogenerated H2O2 to bOH. The Fe3N@NG/NC exhibited outstanding HE-EF performance in removing various organic pollutants with low iron leaching. A removal rate of 97–100% could be obtained for rhodamine B (RhB), dimethyl phthalate, methylene blue, and orange II in 120 min at a pH of 5.0. When the solution pH was set to 3.0, 5.0, 7.0, and 9.0, the removal rate of RhB reached 100%, 96%, 92%, and 81%, respectively, in 60 min at an optimum voltage of 0.0 V (vs. reversible hydrogen electrode (RHE)). Moreover, the concentration of leached iron was expected to be below 0.03 mg/L in a wide pH range of 3.0–9.0. In addition, the RhB removal efficiency remained as high as 90% after six cycles in the reusability experiments. This work highlights the MOF-derived Fe3N composite as an efficient HE-EF catalyst and the corresponding catalytic mechanism, which facilitates its application in wastewater treatment.

We report an in situ synthesis of titanium nitride (Ti3N2Tx) from its carbide (Ti3C2Tx) and concurrently composite formation with N-doped carbon nanotubes (N-CNTs). Unlike conventional wet-chemical method, a simple approach has been adopted for the synthesis of Ti3N2Tx and it’s composite with N-CNTs. The crystallographic study shows an obvious phase transformation from carbide to nitride. Importantly, an optimized composite electrocatalyst (Ti3N2@NCNT(20)-800) exhibits promising oxygen reduction ability under alkaline conditions with positive onset potential (Eonset) of 1.0 V versus reversible hydrogen electrode (RHE) and current density (JL) of 5.3 mA/cm2. The remarkable oxygen reduction reaction (ORR) properties mainly originate from the fascinating carbon-nitrogen exchange (Ti3C2Tx into Ti3N2Tx) in the MXene lattice along with N-doping in CNTs, which eventually lead to the formation of their composite and generating enough active centres for dioxygen adsorption followed by electroreduction. Moreover, the rotating ring disk electrode (RRDE) studies were carried to particularly detect peroxide (HO2−) formation and further to get an insight into ORR kinetics. Additionally, a robust performance of Ti3N2@NCNT(20)-800 electrocatalyst over Pt/C has been observed during the electrochemical cycling stability up to 10,000 (10 k) durable cycles. Thus, we believe that the present methodology provides an adept approach to convert carbide into nitride and further to extend it to synthesize the MXene based composite materials for energy conversion applications.

Of various atomically dispersed metal catalysts, those based on single Ni atoms are among the most efficient electrocatalysts for CO2 reduction. However, the activity of these catalysts is determined by the coordination environment of Ni sites. Here, N and S co-coordinated Ni sites were successfully prepared using a nickel phosphorus trisulfide two-dimensional template to form a sandwich-like conjugated microporous polymer. As-prepared Ni single atom–based porous carbon nanosheets were proved to possess N/S co-coordination via X-ray absorption spectroscopy. As electrocatalysts for CO2 reduction, the prepared porous carbon nanosheets achieved over 95% CO selectivity rate and −7.8 mA cm−2 current density (−0.8 V vs. reversible hydrogen electrode). This performance could be attributed to the sheet-like morphology of the nanosheets with long-distance conductivity and the rich single N/S-coordinated Ni atoms with high activity. The fundamental understanding of manipulating such a coordination environment revealed in this study can be used to create versatile single-metal atom–based catalysts for high-efficient energy conversion.

Alkali-water electrolyzers and hydroxide exchange membrane fuel cells are emerging as promising technologies to realize hydrogen economy. Developing cost-effective electrode materials with high activities towards corresponding hydrogen evolution (HER) and oxidation (HOR) reactions plays a crucial role in commercial hydrogen production and utilization. Herein, we fabricated a V-doped Ni3N/Ni heterostructure (V-Ni3N/Ni) through a controlled nitridation treatment on a V-incorporated nickel hydroxide precursor. The resultant catalyst exhibits comparable catalytic activity and durability to commercial Pt/C in terms of both HER (a low overpotential of 44 mV at the current density of 10 mA·cm−2) and HOR (a high current density of 1.54 mA·cm−2 at 0.1 V versus reversible hydrogen electrode) under alkaline conditions. The superior activity of V-Ni3N/Ni grown on different substrates further implies its intrinsic performance. Density functional theory (DFT) calculations reveal that the coupled metallic Ni and doped V can promote the water adsorption, accelerate the Volmer step of alkaline HER, as well as optimize the adsorption and desorption of hydrogen intermediate (H*) to reach a balanced ΔGH* value.

Exploring the ideal and stable semiconductor material for the efficient photoelectrochemical (PEC) overall water splitting reaction has remained a major challenge. Herein, we develop a facile hydrothermal method for the fabrication of monoclinic Pb3[VO4]2 and orthorhombic PbV2O6 thin films for the efficient and stable PEC overall water splitting applications. Detailed characterization was performed to study the crystal structure and optical, electrical, and electrochemical properties. The band edge positions of Pb3[VO4]2 and PbV2O6 are determined using spectroscopic data, revealing the conduction band edge positioned near the water reduction potential [∼0 V vs reversible hydrogen electrode (RHE)] and the valence band edge positioned well above the water oxidation potential, indicating the possible utilization of photogenerated electrons and holes for efficient water reduction and oxidation, respectively. With the optimized PbV2O6 thin films, a maximum photocurrent of 0.35 mA cm-2 was obtained at 1.23 V versus RHE and the stable production of both O2 and H2 is observed with >90% Faradaic efficiency. Importantly, this work demonstrates the possibility of utilizing lead vanadate materials for PEC water splitting applications.

Electrochemical conversion of CO2 into valuable products is a promising approach. Efficient electrocatalysts are highly desirable but remain to be developed. Here, we proposed a molecular encapsulation strategy to enrich intermediates for facilitating electrochemical conversion of CO2 to C2H4. This strategy is combining M-TCPP [M = FeCl, Co, and Ni; TCPP = tetrakis(4-carboxyphenyl) porphyrin] with a Cu-based metal-organic framework (Cu-MOF) to create a series of metalloporphyrin-decorated Cu catalysts with a coral-like shape (named as M-TCPP@Cu). M-TCPP in the catalysts could supply more CO intermediates to the Cu sites, giving high selectivity for producing C2H4 and lowering overpotentials for CO2 reduction. Meanwhile, the coral-like structure of the catalyst with abundant active sites is conducive to mass diffusion and benefits the conversion of CO2. We realized a higher C2H4 Faradaic efficiency (FE) of 33.42% at -1.17 V versus reversible hydrogen electrode (RHE) on the Fe-TCPP@Cu electrode than that on the sole Cu electrode (16.85%, at -1.27 V vs RHE). Furthermore, due to the encapsulated structure resulted from one-pot reaction that ensures the dispersion of active centers in M-TCPP, metalloporphyrin-decorated Cu catalysts show better performance than the physical mixture of Cu-MOFs and M-TPPs (M = FeCl, Co, and Ni; TPP = 5,10,15,20-tetraphenylporphyrin). The results provide a new strategy for the design of high-performance Cu catalysts from Cu-MOFs for CO2 conversion.

Interactions of electrolyte ions at electrocatalyst surfaces influence the selectivity of electrochemical CO2 reduction (CO2R) to chemical feedstocks like CO. We investigated the effects of anion type in aqueous choline halide solutions (ChCl, ChBr, and ChI) on the selectivity of CO2R to CO over an Ag foil cathode. Using an H-type cell, we observed that halide-specific adsorption at the Ag surface limits CO faradaic efficiency (FECO) at potentials more positive than −1.0 V vs. reversible hydrogen electrode (RHE). At these conditions, FECO increased from I−−−, that is, in the opposite order to the strength of specific adsorption of the halide ions (Cl−−−). At potentials of −1.0 to −1.3 V vs. RHE, restructuring of the Ag surface in ChI and ChCl via dissolution and re-electrodeposition led to more CO-selective Ag facets ([220], [311], and [222]) than in ChBr. This mechanism allowed very high faradaic efficiencies for CO of 97±2 % in ChI and 94±2 % in ChCl to be achieved simultaneously with high current densities at −1.3 V vs. RHE. We also demonstrate that high selectivity to CO (FECO>90 %) in ChCl (at −0.75±0.06 Vvs. RHE) and ChI (at −0.78±0.17 V vs. RHE) could be achieved at a current density of 150 mA cm−2 in a continuous flow-cell electrolyser with Ag nanoparticles on a commercial gas diffusion electrode. This study provides new insights to understand the interactions of anions with catalysts and offers a new method to modify electrocatalyst surfaces.

Platinum is the archetypal electrocatalyst for oxygen reduction—a key reaction in fuel cells and zinc–air batteries. Although dispersing platinum as single atoms on a support is a promising way to minimize the amount required, catalytic activity and selectivity are often low due to unfavourable O2 adsorption. Here we load platinum onto α-Fe2O3 to construct a highly active and stable catalyst with dispersed Pt–Fe pair sites. We propose that the Pt–Fe pair sites have partially occupied orbitals driven by strong electronic coupling, and can cooperatively adsorb O2 and dissociate the O=O bond, whereas OH* can desorb from the platinum site. In alkaline conditions, the catalyst exhibits onset and half-wave potentials of 1.15 V and 1.05 V (versus the reversible hydrogen electrode), respectively, mass activity of 14.9 A mg−1Pt (at 0.95 V) and negligible activity decay after 50,000 cycles. It also shows better performance than 20% Pt/C in a zinc–air battery and H2–O2 fuel cell in terms of specific energy density and platinum utilization efficiency. Atomically dispersed platinum electrocatalysts for oxygen reduction promise minimized platinum usage, but catalytic activity and selectivity are often low due to unfavourable O2 adsorption. To circumvent this issue, Gao and colleagues load platinum onto α-Fe2O3, making a highly active and stable catalyst with dispersed Pt–Fe pair sites.

Electrochemical CO2 reduction reaction (CO2 RR) to multicarbon hydrocarbon and oxygenate (C2+ ) products with high energy density and wide availability is of great importance, as it provides a promising way to achieve the renewable energy storage and close the carbon cycle. Herein we design a Cu-CuI composite catalyst with abundant Cu0 /Cu+ interfaces by physically mixing Cu nanoparticles and CuI powders. The composite catalyst achieves a remarkable C2+ partial current density of 591 mA cm-2 at -1.0 V vs. reversible hydrogen electrode in a flow cell, substantially higher than Cu (329 mA cm-2 ) and CuI (96 mA cm-2 ) counterparts. Induced by alkaline electrolyte and applied potential, the Cu-CuI composite catalyst undergoes significant reconstruction under CO2 RR conditions. The high-rate C2+ production over Cu-CuI is ascribed to the presence of residual Cu+ and adsorbed iodine species which improve CO adsorption and facilitate C-C coupling.

Fe-N-C-based electrocatalysts have been developed as an encouraging substitute compared to their expensive Pt-containing equivalents for the oxygen reduction reaction (ORR). However, they still face major durability challenges from the in- situ production of Fenton radicals. Therefore, the synthesis of Fe-free ORR catalysts is among the emerging concerns. Herein, we have precisely applied a multistep heating strategy to produce mesoporous N-doped carbon nanostructures with Mn-/Co-Nx dual moieties from mixed-metal zeolitic imidazolate frameworks (ZIFs). It is found that their unique structure, with dual-metallic active sites, not only offers a high electrochemical performance for the ORR (E1/2 = 0.83 V vs reversible hydrogen electrode (RHE) in acid media), but also enhances the operational durability of the catalyst after 20 000 cycles with 97% of retention and very low H2O2 production (

The reduction of carbon dioxide (CO2 ) into value-added fuels using an electrochemical method has been regarded as a compelling sustainable energy conversion technology. However, high-performance electrocatalysts for CO2 reduction reaction (CO2 RR) with high formate selectivity and good stability need to be improved. Earth-abundant Bi has been demonstrated to be active for CO2 RR to formate. Herein, we fabricated an extremely active and selective bismuth nanosheet (Bi-NSs) assembly via an in situ electrochemical transformation of (BiO)2 CO3 nanostructures. The as-prepared material exhibits high activity and selectivity for CO2 RR to formate, with nearly 94% faradaic efficiency at -1.03 V (versus reversible hydrogen electrode (vs. RHE)) and stable selectivity (>90%) in a large potential window ranging from -0.83 to -1.18 V (vs. RHE) and excellent durability during 12 h continuous electrolysis. In addition, the Bi-NSs based CO2 RR/methanol oxidation reaction (CO2 RR/MOR) electrolytic system for overall CO2 splitting was constructed, evidencing the feasibility of its practical implementation.

Transition metal- and nitrogen-codoped graphene (referred to as M-N-G, where M is a transition metal) has emerged as an important type of single-atom catalysts with high selectivities and activities for electrochemical CO2 reduction (CO2 R) to CO. However, despite extensive previous studies on the catalytic origin, the active site in M-N-G catalysts remains puzzling. In this study, density functional theory calculations and computational hydrogen electrode model is used to investigate CO2 R reaction energies on Zn-N-G, which exhibits outstanding catalytic performance, and to examine kinetic barriers of reduction reactions by using the climbing image nudged elastic band method. We find that single Zn atoms binding to N and C atoms in divacancy sites of graphene cannot serve as active sites to enable CO production, owing to *OCHO formation (* denotes an adsorbate) at an initial protonation process. This contradicts the widely accepted CO2 R mechanism whereby single metal atoms are considered catalytic sites. In contrast, the C atom that is the nearest neighbor of the single Zn atom (CNN ) is found to be highly active and the Zn atom plays a role as an enhancer of the catalytic activity of the CNN . Detailed analysis of the CO2 R pathway to CO on the CNN site reveals that *COOH is favorably formed at an initial electrochemical step, and every reaction step becomes downhill in energy at small applied potentials of about -0.3 V with respect to reversible hydrogen electrode. Electronic structure analysis is also used to elucidate the origin of the CO2 R activity of the CNN site.

Direct photoelectrochemical (PEC) water splitting is of prime importance in sustainable energy conversion systems; however, it is a big challenge to simultaneously control light harvesting and charge transport for the improvement of PEC performance. Herein, we report a three-dimensional ordered macroporous (3DOM) CsTaWO6-xNx inverse opal array as a promising candidate for the first time. To address the critical challenge, an ultrathin carbon-nitride-based layer-intercalated 3DOM CsTaWO6-xNx architecture as a conformal heterojunction photoanode was assembled. This state-of-the-art conformal heterojunction photoanode with carrier-separation efficiency up to 88% achieves a high current density of 4.59 mA cm-2 at 1.6 V versus a reversible hydrogen electrode (vs RHE) under simulated AM 1.5G illumination, which is approximately 3.4 and 17 times larger than that of pristine CsTaWO6-xNx inverse opals and powers photoelectrodes in alkaline media, corresponding to an incident photon-to-current efficiency of 32% at 400 nm and outstanding stability for PEC water splitting. Density functional theory calculations propose that the intimate interface of a conformal photoanode optimizes the charge separation and transfer, thus enhancing the intrinsic water oxidation performance. This work enables us to elucidate the pivotal importance of 3DOM architectures and conformal heterostructures and the promising contributions to excellent PEC water-splitting applications.

Developing efficient and low-cost electrocatalysts is essential for the electroreduction of N2 to NH3. Here, highly monodispersed MoO3 clusters loaded on a coral-like CeOx compound with abundant oxygen vacancies are successfully prepared by an impregnation–reduction method. The MoO3 clusters with small sizes of 2.6 ± 0.5 nm are induced and anchored by the oxygen vacancies of CeOx, resulting in excellent nitrogen reduction reaction (NRR) performance. Additionally, the synergistic effects between MoO3 and CeOx lead to a further improvement of the electrochemical performance. The as-prepared MoO3–CeOx catalyst shows an NH3 yield rate of 32.2 μg h−1 mgcat−1 and a faradaic efficiency of 7.04% at −0.75 V (vs. reversible hydrogen electrode) in 0.01 M Dulbecco's Phosphate Buffered Saline. Moreover, it displays decent electrochemical stability over 30,000 s. Besides, the electrochemical NRR mechanism for MoO3–CeOx is investigated by in-situ Fourier transform infrared spectroscopy. N–H stretching, H–N–H bending, and N–N stretching are detected during the reaction, suggesting that an associative pathway is followed. This work provides an approach to designing and synthesizing potential electrocatalysts for NRR.

Low-cost catalysts with high activity are in immediate demand for energy storage and conversion devices. In this study, polyvinyl pyrrolidone was used as a complexing agent to synthesize La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) perovskite oxide. The obtained porous layered LSCF has a large specific surface area of 23.74 m2/g, four times higher than that prepared by the traditional sol-gel method (5.08 m2/g). The oxygen reduction reaction activity of the oxide in 0.1 mol/L KOH solution was studied using a rotating ring-disk electrode. In the tests, the initial potential of 0.88 V (vs. reversible hydrogen electrode) and the limiting diffusion current density of 5.02 mA/cm2 were obtained at 1600 r/min. Therefore, higher catalytic activity and stability were demonstrated, compared with the preparation of LSCF perovskite oxide by the traditional method.

Developing of economic and efficient catalysts is critical for the application of electroreduction of carbon dioxide to highly valuable chemicals. Herein, we present a facile method to synthesize N-doped hieratically porous carbon through pyrolysis of petroleum pitch followed by ammonia etching. We found mesopores are favored formation by removing of asphaltene from petroleum pitch during the carbonation process. Simultaneously, ammonia etching can not only increase the pyridinic-N content, but also upgrade the ratio of meso- to micro- pores of carbon materials. Using the N-doped hieratically porous carbon as catalyst for carbon dioxide electroreduction, the Faradaic efficiency of carbon monoxide reaches 83% at −0.9 V vs. the reversible hydrogen electrode (RHE) in 0.1 M KHCO3. This superior performance is attributed to the synergistic effects of highly pyridinic-N content in conjunction with the hieratically porous architecture, rendering abundant exposed and accessible active sites for electroreduction of CO2. Our work provides a new strategy for the large-scale preparation of high-performance, low-cost catalysts for CO2 electroreduction.

Photoelectrochemical (PEC) water splitting for solar energy conversion into chemical fuels has attracted intense research attention. The semiconductor hematite (α-Fe2O3), with its earth abundance, chemical stability, and efficient light harvesting, stands out as a promising photoanode material. Unfortunately, its electron affinity is too deep for overall water splitting, requiring additional bias. Interface engineering has been used to reduce the onset potential of hematite photoelectrode. Here we focus instead on energy band engineering hematite by shrinking the crystal lattice, and the water-splitting onset potential can be decreased from 1.14 to 0.61 V vs. the reversible hydrogen electrode. It is the lowest record reported for a pristine hematite photoanode without surface modification. X-ray absorption spectroscopy and magnetic properties suggest the redistribution of 3d electrons in the as-synthesized grey hematite electrode. Density function theory studies herein show that the smaller-lattice-constant hematite benefits from raised energy bands, which accounts for the reduced onset potential.

Z-scheme photocatalytic system has been regarded as a popular field of research in photoelectrochemical (PEC) water splitting. Among the many obstacles facing a Z-scheme photocatalytic system, the analysis methods of interfacial Z-scheme charge transfer still remain a significant challenge. Hence, in this study, CdS/Ti-Fe2O3 heterojunction photoanodes are elaborately designed to explore the charge-transfer behavior in PEC water splitting. In this study, photophysical measurements, including the Kelvin probe measurement, surface photovoltage spectroscopy (SPV), and transient photovoltage spectroscopy (TPV), are used to monitor the migration behavior of photogenerated charges at the interface electric field of CdS/Ti-Fe2O3 Z-scheme heterojunction photoanodes. The Kelvin probe and SPV measurements demonstrate that CdS/Ti-Fe2O3 interfacial driving force favors the rapid transfer of photoexcited electrons to CdS. The double-beam strategy based on TPV indicates that more electrons of Ti-Fe2O3 are combined with the holes of CdS owing to the intensive interface electric field. The results of these measurements successfully prove the Z-scheme migration mechanism of CdS/Ti-Fe2O3 photoanodes. Benefiting from the desirable charge transfer at the interface electric field, CdS/Ti-Fe2O3 photoanodes exhibit superior photocatalytic oxygen evolution reaction performance compared with that of pure Ti-Fe2O3. The photocurrent density of the 25CdS/Ti-Fe2O3 photoanode reaches 1.94 mA/cm2 at 1.23 V versus reversible hydrogen electrode without excess cocatalyst, and it is two times higher than that of pure Ti-Fe2O3 photoanode. Therefore, an outstanding strategy is provided in this study to prove the Z-scheme charge-transfer mechanism of photocatalytic systems in PEC water splitting.

Electrocatalytic N2 reduction is deemed as a prospective strategy toward low-carbon and environmentally friendly NH3 production under mild conditions, but its further application is still plagued by low NH3 yield and poor faradaic efficiency (FE). Thus, electrocatalysts endowing with high activity and satisfying selectivity are highly needed. Herein, Bi nanoparticles in situ confined in carbon rods (Bi NPs@CRs) are reported, which are fabricated via thermal annealing of a Bi-MOF precursor as a high-efficiency electrocatalyst for artificial NH3 synthesis with favorable selectivity. Such an electrocatalyst conducted in 0.1 M HCl achieves a high FE of 11.50% and a large NH3 yield of 20.80 μg h-1 mg-1cat. at -0.55 and -0.60 V versus reversible hydrogen electrode, respectively, which also possesses high electrochemical durability.

CO methanation from electrochemical CO reduction reaction (CORR) is significant for sustainable environment and energy, but electrocatalysts with excellent selectivity and activity are still lacking. Selectivity is sensitive to the structure of active sites, and activity can be tailored by work function. Moreover, intrinsic active sites usually possess relatively high concentration compared to artificial ones. Here, antisite defects Mo S2 and W S2 , intrinsic atomic defects of MoS 2 and WS 2 with a transition metal atom substituting a S 2 column, are investigated for CORR by density functional theory calculations. The steric hindrance from the special bowl structure of Mo S2 and W S2 ensures good selectivity towards CO methanation. Coordination environment variation of the active sites, the under-coordinated Mo or W atoms, effectively lowers the work function, making Mo S2 and W S2 highly active for CO methanation with the required potential of -0.47 and -0.49 V vs. reversible hydrogen electrode, respectively. Moreover, high concentration of active sites and minimal structural deformation during the catalytic process of Mo S2 and W S2 enhance their attraction for future commercial application.

The methodology of coating electrocatalysts on semiconductor substrates is critical for the catalytic performance of photoelectrochemical electrodes. A weakly bound coating leads to orders of magnitude lower efficiency and reliability compared to those required to meet the commercial demand. Herein, a facile strategy based on the hydrolysis of TiCl4 is developed to solve the coating issue. Mesoporous tungsten phosphide (WP) particles were spin-coated and affixed onto TiO2-protected planar p-Si by the formation of a TiO2 necking layer between the catalyst particles and the substrates. Under 1 sun illumination, the as-prepared WP/TiO2/Si photocathode yields a saturated current density of -35 mA cm-2 and a durability of over 110 h with a current density over -15 mA cm-2 at 0 V versus a reversible hydrogen electrode in a 1.0 M KOH solution, which is among the state-of-the-art performances of commercial planar Si-based photocathodes. The Kelvin probe force microscopy results suggest the successive transfer of photoelectrons from Si to TiO2 and WP. The as-formed TiO2 necking layer plays the key role in ensuring the surface catalytic activity and durability. This necking strategy is also applicable for coating other transition-metal phosphides, for example, MoP and FeP, thus offering a practical approach to meet the commercial requirement of low-cost, highly efficient, and durable photoelectrodes.

Electrochemical nitrogen reduction reaction (NRR) is a promising method for synthesizing ammonia (NH3). However, due to the extremely strong N≡N bond and the competing hydrogen evolution reaction (HER), the electrochemical NRR process remains a great challenge in achieving a high NH3 yielding rate and a high Faradaic efficiency (FE). Recently, either Bi-based or W-based catalysts have been used in N2 fixation due to lower HER activity. To further promote N2 activation, we develop a simple protocol to introduce and adjust the crystal defects in the host lattice of Bi2WO6 nanoflowers via adjusting the amount of Ce dopant (denoted as xCe-Bi2WO6, where x represents the designed mole percentage of Ce). At -0.20 V versus the reversible hydrogen electrode (RHE), 10%Ce-Bi2WO6 manifests a high NH3 yielding rate (22.5 μg h-1 mg-1cat.), a high FE (15.9%), and excellent electrochemical and structure durability. Its performance is better than most previously reported Bi-based and W-based electrocatalysts for NRR in aqueous solutions. According to density functional theory (DFT) calculations, the introduction of crystal defects into Bi2WO6 can strengthen the adsorption and activation of N2, thus leading to a significant increase in NRR activity.

Electrocatalytic conversion of nitrate (NO3-) into ammonia can not only eliminate harmful pollutant but also provide a green method for a low-temperature ammonia synthesis. The electrochemical NO3- reduction reactions (NO3RRs) of a series of transition-metal-doped hexagonal boron phosphide (h-BP) monolayers were comprehensively evaluated using density functional theory. The V-doped h-BP monolayer was found to stand near the top of the volcano plot with the limiting potential of -0.22 V versus a reversible hydrogen electrode, exhibiting the lowest overpotential among the investigated systems in this work. Besides, the competing hydrogen evolution reaction is significantly suppressed due to the weak adsorption of the H atom. Importantly, the structure of the V-doped h-BP monolayer can be retained very well until 900 K, illustrating the initial indication of high thermal stability and great promise for synthesis. This study not only offers an eligible NO3RR electrocatalyst but also provides an atomic understanding of the behind mechanisms of the NO3RR process.

Ferrihydrite (Fh) has been demonstrated as an effective interfacial layer for photoanodes to achieve outstanding photoelectrochemical (PEC) performance for water oxidation reaction owing to its unique hole-storage function. However, it is unknown whether such a hole-storage layer can be used to construct highly efficient photocathodes for hydrogen evolution reaction (HER). In this work, we report Fh interfacial engineering of amorphous silicon photocathode (with nickel as HER cocatalyst) achieving a photocurrent density of 15.6 mA cm-2 at 0 V vs. the reversible hydrogen electrode and a half-cell energy conversion efficiency of 4.08 % in alkaline solution, outperforming most of reported a-Si based photocathodes including multi-junction configurations integrated with noble metal cocatalysts in acid solution. Besides, the photocurrent density is maintained above 14 mA cm-2 for 175 min with 100 % Faradaic efficiency for HER in alkaline solution. Our results demonstrate a feasible approach to construct efficient photocathodes via the application of a hole-storage layer.

Cu2SnxGe1-xS3 (CTGS) particles were synthesized via a solid-state reaction and assessed, for the first time, as both photocatalysts and photocathode materials for hydrogen evolution from water. Variations in the crystal and electronic structure with the Sn/Ge ratio were examined experimentally and theoretically. The incorporation of Ge was found to negatively shift the conduction band minimum, such that the bandgap energy could be tuned over the range 0.77-1.49 eV, and also increased the driving force for the photoexcited electrons involved in hydrogen evolution. The effects of the Sn/Ge ratio and of Cu deficiency on the photoelectrochemical performance of Cu2SnxGe1-xS3 and CuySn0.38Ge0.62S3 (1.86 < y < 2.1) based photocathodes were evaluated under simulated sunlight. Both variations in the band-edge position and the presence of a secondary impurity phase affected the performance, such that a particulate Cu1.9Sn0.38Ge0.62S3 photocathode was the highest performing specimen. This cathode gave a half-cell solar-to-hydrogen energy conversion efficiency of 0.56% at 0.18 V vs a reversible hydrogen electrode (RHE) and an incident-photon-to-current conversion efficiency of 18% in response to 550 nm monochromatic light at 0 VRHE. More importantly, these CTGS particles also demonstrated significant photocatalytic activity during hydrogen evolution and were responsive to radiation up to 1500 nm, representing infrared light. The chemical stability, lack of toxicity, and high activity during hydrogen evolution of the present CTGS particles suggest that they may be potential alternatives to visible/infrared light responsive Cu-chalcogenide photocatalysts and photocathode materials such as Cu(In,Ga)(S,Se)2 and Cu2ZnSnS4.

Electrochemical carbon dioxide (CO 2 ) reduction reaction (CO 2 RR) is an attractive approach to deal with the excessive emission of CO 2 and to produce valuable fuels and chemicals in a carbon-neutral way. Many efforts have been devoted to boost the activity and selectivity of high-value multicarbon products (C 2+ ) on Cu-based electrocatalysts. However, Cu-based CO 2 RR electrocatalysts suffer from poor catalytic stability mainly due to the structural degradation and loss of active species under CO 2 RR condition. To date, most reported Cu-based electrocatalysts present stabilities over dozens of hours, which limits the advance of Cu-based electrocatalysts for CO 2 RR. Here, a porous chlorine-doped Cu electrocatalyst is reported and exhibits high C 2+ Faradaic efficiency (FE) of 53.8% at -1.00 V versus reversible hydrogen electrode (V RHE ). Importantly, the catalyst exhibited an outstanding catalytic stability in long-term electrocatalysis over 240 hours. Experimental results show that the chlorine-induced stable cationic Cu 0 -Cu + species and the well-preserved structure with abundant active sites are found to be critical to maintain the high FE of C 2+ in the long-term run of electrochemical CO 2 reduction.

A transparent Ta₃N₅ photoanode is a promising candidate for the front-side photoelectrode in a photoelectrochemical (PEC) cell with tandem configuration (tandem cell), which can potentially provide high solar-to-hydrogen (STH) energy conversion efficiency. This study focuses in particular on the semiconductor properties and interfacial design of transparent Ta₃N₅ photoanodes fabricated on insulating quartz substrates (Ta₃N₅/SiO₂), typically the geometric area of 1 × 1 cm² in contact with indium on its edge. This material utilizes the self-conductivity of Ta₃N₅ to make the PEC system operational, and the electrode would strongly reflect the intrinsic nature of Ta₃N₅ without a back contact that is commonly introduced. First, PEC measurements using acetonitrile (ACN)/H₂O mixed solution were made to elucidate the intrinsic photoresponse in the presence of tris(2,2′-bipyridine)ruthenium(II) bis(hexafluorophosphate) (Ru(bpy)₃(PF₆)₂) without water contact which avoids a multielectron-transfer oxygen evolution reaction (OER) and photoinduced self-oxidation. The potential difference between the onset potential of Ru²⁺ PEC oxidation by Ta₃N₅/SiO₂ and the redox potential of Ru²⁺/³⁺ in the nonaqueous environment was about 0.7 V. While a stable photoanodic response was observed for Ta₃N₅/SiO₂ in the nonaqueous phase, the addition of a small quantity of water into this nonaqueous system led to the immediate deactivation of Ta₃N₅/SiO₂ photoanode under illumination by self-photooxidation to form TaOₓ at the solid/water interface. In aqueous phase, flatband potentials estimated from Mott–Schottky analysis varied with solution pH (constant potential against reversible hydrogen electrode (RHE)). Photoelectrode modification by a transparent NiFeOₓ layer was attempted. The complete coverage of the Ta₃N₅ surface with transparent NiFeOₓ electrocatalysts, achieved by an optimized spin-coating protocol with controlled Ni–Fe precursors, allowed for the successful protection of Ta₃N₅ and demonstrated an extremely stable photocurrent for hours without any additional protective layers. The stability of the resultant NiFeOₓ/Ta₃N₅/SiO₂ was limited not by Ta₃N₅ but mainly by a NiFeOₓ electrocatalyst due to Fe dissolution with time.

Electrocatalytic nitrogen fixation under ambient conditions represents an energy-saving sustainable alternative strategy to the energy-consuming traditional Haber–Bosch process toward ammonia synthesis. However, the traditional electrocatalysts for nitrogen reduction reaction (NRR) often suffer low selectivity and low activity. From quantum-mechanical calculations, we obtain a benefit clue that the Ni atom adsorbed by the first hydrogen ion in the catalyst exhibits selectivity for the adsorption of N2 and other H atoms, and it preferentially adsorbs N2 molecules. Thus, we propose an interfacial engineering strategy to simultaneously accelerate selectivity and activity using metal/metal hydroxide. The remarkable activity of metal/metal hydroxide originates from its synergized water dissociation and unique hydrogenation pathway of metal hydride. The priority absorption of the N2 suppresses the competitive hydrogen evolution reaction and accelerates the kinetics to generate ∗N2H: ∗H + N2 → ∗N2H, which a is rate-limiting step for NH3 synthesis. Using Ni/NiFe–OH as prototypes, here we show that selectivity and catalytic activity are simultaneously enhanced, surprisingly, in simple inorganic hybrid and confers exceptionally Faradaic efficiency of 23.34% and NH3 yield 19.74 μg h−1 cm−2 at −0.15 V versus reversible hydrogen electrode (RHE) in 0.5 M KOH electrolyte under ambient conditions. The long-term durability is also excellent. This work provides a possibility for the rational design of efficient electrocatalysts for N2 electrochemical reduction with a large-scale production.

The stability and activity of the catalysts are crucial for the oxygen reduction reaction (ORR) in fuel cells. Herein, CoFe/N, S-codoped biomass carbon (FB-CoFe-700) with graphitic nanoribbons and multiple CoFe nanoparticles was prepared through a facile thermal pyrolysis followed by an acid treatment process. The evolution of the growth of metal nanoparticles with the formation of graphite during the carbonization process was investigated. Inseparable from graphitic carbon-encased metal nanoparticles with the coexistence of graphitized nanoribbons and graphene-like sheets, FB-CoFe-700 exhibited a remarkable long-term electrocatalytic stability with 90.7% current retention after 50 000 s much superior to that of the commercially available Pt/C (20 wt %) in an alkaline medium. Meanwhile, FB-CoFe-700 displayed promising ORR catalytic activity (E0 = 0.92 V vs reversible hydrogen electrode (RHE), E1/2 = 0.82 V vs RHE, and n = 3.97) very similar to that of commercial Pt/C and outstanding methanol tolerance in an alkaline medium. This work is helpful for further development of nonprecious metal-doped carbon electrocatalysts with long-term stability.

Application of noble metal-free electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) during electrocatalytic water splitting is crucial for clean energy conversion and has drawn extensive attention. However, the development of highly active and low cost electrocatalysts is a considerable challenge. Herein, Co-Cu alloy nanoparticles-incorporated carbon nanowires electrocatalyst was synthesized and evaluated for both OER and HER. The nanomaterials were fabricated by facile electrospinning of sol-gel composed of cobalt acetate, copper acetate, and poly(vinyl alcohol) followed by calcination in an inert environment. Adjusting the composition of the metallic counterpart was found to significantly enhance electrochemical properties of the catalyst. Furthermore, the unique nanowire morphology and structural properties of incorporated Co-Cu alloy, the (Co0.95Cu0.05@CNWs) composition exhibits good electrocatalytic performance for both OER and HER in the alkaline medium. Physicochemical characterizations using X-ray diffraction, X-ray photoelectron spectroscope, scanning electron microscopy, and transmission electron microscopy have confirmed the formation of alloy structure and nanowire morphology. The optimum composition (Co0.95Cu0.05@CNWs) requires small overpotential, ɳ10 of ∼285 mV for oxygen evolution reaction (OER) and ∼160 mV for hydrogen evolution reaction (HER) with the corresponding Tafel slope of 92 mV dec−1 and 172 mV dec−1 versus the reversible hydrogen electrode, respectively. In addition, only negligible loss in activity was observed after 1000 cycles and prodeces cell voltage of 1.58 V at current of 10 mA/cm2 and 1.72 V at current density of 50 mA/cm2 in two electrode system. Density Functional Theory (DFT) calculations were employed to verify experimental results. Electronic density of states (DOS) results reveal an increase in electronic states near the Fermi level upon Co-Cu heterojunctioning with CNWs. This is indicative of improved catalytic activity and more favorable binding energies of HER and OER intermediates. Reaction coordinate diagrams for HER and OER were developed, which aided in identifying thermodynamically limiting steps. This work may provide a feasible approach for incorporating other transition metals to design low-cost and high-performance bifunctional electrocatalysts for overall water splitting.