Hf and Co Dual Single Atoms Co-Doped Carbon Catalyst Enhance the Oxygen Reduction Performance.

Single-atom metal-doped M-N-C (M═Fe, Co, Mn, or Ni) catalysts exhibit excellent catalytic activity toward oxygen reduction reactions (ORR). However, their performance still has a large gap considering the demand for their practical applications. This study reports a high-performance dual single-atom doped carbon catalyst (HfCo-N-C), which is prepared by pyrolyzing Co and Hf co-doped ZIF-8 . Co and Hf are atomically dispersed in the carbon framework and coordinated with N to form Co-N4 and Hf-N4 active moieties. The synergetic effect between Co-N4 and Hf-N4 significantly enhance the catalytic activity and durability of the catalyst. In an acidic medium, the ORR half-wave potential (E1/2 ) of the catalyst is up to 0.82 V , which is much higher than that of the Co-N-C catalyst without Hf co-doping (0.80 V). The kinetic current density of the catalyst is up to 2.49 A cm-2 at 0.85 V , which is 1.74 times that of the Co-N-C catalyst without Hf co-doping. Moreover, the catalyst exhibits excellent cathodic performance in single proton exchange membrane fuel cells and Zn-air batteries. Furthermore, Hf co-doping can effectively suppress the formation of H2 O2 , resulting in significantly improved stability and durability.

Surface engineering of two-dimensional hexagonal boron-nitride for optoelectronic devices.

Two-dimensional hexagonal boron nitride (2D h-BN) is being extensively studied in optoelectronic devices due to its electronic and photonic properties. However, the controlled optimization of h-BN's insulating properties is necessary to fully explore its potential in energy conversion and storage devices. In this work, we engineered the surface of h-BN nanoflakes via one-step in situ chemical functionalization using a liquid-phase exfoliation approach. The functionalized h-BN (F-h-BN) nanoflakes were subsequently dispersed on the surface of TiO2 to tune the TiO2/QDs interface of the optoelectronic device. The photoelectrochemical (PEC) devices based on TiO2/F-h-BN/QDs with optimized addition of carbon nanotubes (CNTs) and scattering layers showed 46% improvement compared to the control device (TiO2/QDs). This significant improvement is attributed to the reduced trap/carrier recombination and enhanced carrier injection rate of the TiO2-CNTs/F-h-BN/QDs photoanode. Furthermore, by employing an optimized TiO2-CNTs/F-h-BN/QDs photoanode, QDs-sensitized solar cells (QDSCs) yield an 18% improvement in photoconversion efficiency. This represents a potential and adaptability of our approach, and pathway to explore surface-engineered 2D materials to optimize the interface of solar energy conversion and other emerging optoelectronic devices.

Practicable Zn metal batteries enabled by ultrastable ferromagnetic interface.

Rechargeable zinc (Zn) metal batteries (RZMBs) are demonstrated as sustainable and low-cost alternative in the energy storage industry of the future. However, the elusive Zn deposition behavior and water-originated parasitic reactions bring significant challenges to the fabrication and commercialization of Zn anodes, especially under high plating/stripping capacity. In this work, the ferromagnetic interface in conjunction with the magnetic field (MF) to effectively address these fabrication hurdles is proposed. The introduction of ferromagnetic layer with high chemical durability not only maintains the long-term regulating deposition steadily by magnetic field, but also plays a significant role in preventing side reactions, hence reducing gas production. These merits allow Zn-anode to achieve over 350 h steady Zn-deposition with a depth of discharge (DODZn) up to 82% and translates well to ZnFe-MF||V2O5 full cells, supporting stable cycling at high mass loading of 13.1 mg/cm2, which makes RZMBs configurations promising for commercial applications.

Interface Engineering of NixSy@MnOxHy Nanorods to Efficiently Enhance Overall-Water-Splitting Activity and Stability.

HIGHLIGHTS: Three-dimensional (3D) core-shell heterostructured NixSy@MnOxHy nanorods grown on nickel foam (NixSy@MnOxHy/NF) were successfully fabricated via a simple hydrothermal reaction and a subsequent electrodeposition process. The fabricated NixSy@MnOxHy/NF shows outstanding bifunctional activity and stability for hydrogen evolution reaction and oxygen evolution reaction, as well as overall-water-splitting performance. The main origins are the interface engineering of NixSy@MnOxHy, the shell-protection characteristic of MnOxHy, and the 3D open nanorod structure, which remarkably endow the electrocatalyst with high activity and stability. Exploring highly active and stable transition metal-based bifunctional electrocatalysts has recently attracted extensive research interests for achieving high inherent activity, abundant exposed active sites, rapid mass transfer, and strong structure stability for overall water splitting. Herein, an interface engineering coupled with shell-protection strategy was applied to construct three-dimensional (3D) core-shell NixSy@MnOxHy heterostructure nanorods grown on nickel foam (NixSy@MnOxHy/NF) as a bifunctional electrocatalyst. NixSy@MnOxHy/NF was synthesized via a facile hydrothermal reaction followed by an electrodeposition process. The X-ray absorption fine structure spectra reveal that abundant Mn-S bonds connect the heterostructure interfaces of NixSy@MnOxHy, leading to a strong electronic interaction, which improves the intrinsic activities of hydrogen evolution reaction and oxygen evolution reaction (OER). Besides, as an efficient protective shell, the MnOxHy dramatically inhibits the electrochemical corrosion of the electrocatalyst at high current densities, which remarkably enhances the stability at high potentials. Furthermore, the 3D nanorod structure not only exposes enriched active sites, but also accelerates the electrolyte diffusion and bubble desorption. Therefore, NixSy@MnOxHy/NF exhibits exceptional bifunctional activity and stability for overall water splitting, with low overpotentials of 326 and 356 mV for OER at 100 and 500 mA cm-2, respectively, along with high stability of 150 h at 100 mA cm-2. Furthermore, for overall water splitting, it presents a low cell voltage of 1.529 V at 10 mA cm-2, accompanied by excellent stability at 100 mA cm-2 for 100 h. This work sheds a light on exploring highly active and stable bifunctional electrocatalysts by the interface engineering coupled with shell-protection strategy.

Phosphorus-Doped Graphene Electrocatalysts for Oxygen Reduction Reaction.

Developing cheap and earth-abundant electrocatalysts with high activity and stability for oxygen reduction reactions (ORRs) is highly desired for the commercial implementation of fuel cells and metal-air batteries. Tremendous efforts have been made on doped-graphene catalysts. However, the progress of phosphorus-doped graphene (P-graphene) for ORRs has rarely been summarized until now. This review focuses on the recent development of P-graphene-based materials, including the various synthesis methods, ORR performance, and ORR mechanism. The applications of single phosphorus atom-doped graphene, phosphorus, nitrogen-codoped graphene (P, N-graphene), as well as phosphorus, multi-atoms codoped graphene (P, X-graphene) as catalysts, supporting materials, and coating materials for ORR are discussed thoroughly. Additionally, the current issues and perspectives for the development of P-graphene materials are proposed.

MnOx -Decorated Nickel-Iron Phosphides Nanosheets: Interface Modifications for Robust Overall Water Splitting at Ultra-High Current Densities.

Exploring highly active and stable bifunctional water-splitting electrocatalysts at ultra-high current densities is remarkably desirable. Herein, 3D nickel-iron phosphides nanosheets modified by MnOx nanoparticles are grown on nickel foam (MnOx /NiFeP/NF). Resulting from the electronic coupling effect enabled by interface modifications, the intrinsic activities of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are improved. Meanwhile, 3D nanosheets provide abundant active sites for HER and OER, leading to accelerating the reaction kinetics. Besides, the shell-protection characteristic of MnOx improves the durability of MnOx /NiFeP/NF. Therefore, MnOx /NiFeP/NF shows exceptional bifunctional electrocatalytic activities toward HER (an overpotential of 255 mV at 500 mA cm-2 ), OER (overpotentials of 296 and 346 mV at 500 and 1000 mA cm-2 , respectively), and overall water splitting (cell voltages of 1.796 and 1.828 V at 500 and 1000 mA cm-2 , respectively). Furthermore, it owns remarkably outstanding stability for overall water splitting at ultra-high current densities (120 and 70 h at 500 and 1000 mA cm-2 , respectively), which outperforms almost all of the non-noble metal electrocatalysts. This work presents efficient strategies of interface modifications, 3D nanostructures, and shell protection to afford ultra-high current densities.

Atomically Dispersed Transition Metal-Nitrogen-Carbon Bifunctional Oxygen Electrocatalysts for Zinc-Air Batteries: Recent Advances and Future Perspectives.

Rechargeable zinc-air batteries (ZABs) are currently receiving extensive attention because of their extremely high theoretical specific energy density, low manufacturing costs, and environmental friendliness. Exploring bifunctional catalysts with high activity and stability to overcome sluggish kinetics of oxygen reduction reaction and oxygen evolution reaction is critical for the development of rechargeable ZABs. Atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts possessing prominent advantages of high metal atom utilization and electrocatalytic activity are promising candidates to promote oxygen electrocatalysis. In this work, general principles for designing atomically dispersed M-N-C are reviewed. Then, strategies aiming at enhancing the bifunctional catalytic activity and stability are presented. Finally, the challenges and perspectives of M-N-C bifunctional oxygen catalysts for ZABs are outlined. It is expected that this review will provide insights into the targeted optimization of atomically dispersed M-N-C catalysts in rechargeable ZABs.

Atomically Dispersed Fe-Co Bimetallic Catalysts for the Promoted Electroreduction of Carbon Dioxide.

The electroreduction reaction of CO2 (ECO2RR) requires high-performance catalysts to convert CO2 into useful chemicals. Transition metal-based atomically dispersed catalysts are promising for the high selectivity and activity in ECO2RR. This work presents a series of atomically dispersed Co, Fe bimetallic catalysts by carbonizing the Fe-introduced Co-zeolitic-imidazolate-framework (C-Fe-Co-ZIF) for the syngas generation from ECO2RR. The synergistic effect of the bimetallic catalyst promotes CO production. Compared to the pure C-Co-ZIF, C-Fe-Co-ZIF facilitates CO production with a CO Faradaic efficiency (FE) boost of 10%, with optimal FECO of 51.9%, FEH2 of 42.4% at - 0.55 V, and CO current density of 8.0 mA cm-2 at - 0.7 V versus reversible hydrogen electrode (RHE). The H2/CO ratio is tunable from 0.8 to 4.2 in a wide potential window of - 0.35 to - 0.8 V versus RHE. The total FECO+H2 maintains as high as 93% over 10 h. The proper adding amount of Fe could increase the number of active sites and create mild distortions for the nanoscopic environments of Co and Fe, which is essential for the enhancement of the CO production in ECO2RR. The positive impacts of Cu-Co and Ni-Co bimetallic catalysts demonstrate the versatility and potential application of the bimetallic strategy for ECO2RR.

Nanostructured Cobalt-Based Electrocatalysts for CO2 Reduction: Recent Progress, Challenges, and Perspectives.

CO2 reduction reaction (CO2 RR) provides a promising strategy for sustainable carbon fixation by converting CO2 into value-added fuels and chemicals. In recent years, considerable efforts are focused on the development of transition-metal (TM)-based catalysts for the selectively electrochemical CO2 reduction reaction (ECO2 RR). Co-based catalysts emerge as one of the most promising electrocatalysts with high Faradaic efficiency, current density, and low overpotential, exhibiting excellent catalytic performance toward ECO2 RR for CO and HCOOH productions that are economically viable. The intrinsic contribution of Co and the synergistic effects in Co-hybrid catalysts play essential roles for future commercial productions by ECO2 RR. This review summarizes the rational design of Co-based catalysts for ECO2 RR, including molecular, single-metal-site, and oxide-derived catalysts, along with the nanostructure engineering techniques to highlight the distribution of the ECO2 RR products by Co-based catalysts. The density functional theory (DFT) simulations and advanced in situ characterizations contribute to interpreting the synergies between Co and other materials for the enhanced product selectivity and catalytic activity. Challenges and outlook concerning the catalyst design and reaction mechanism, including the upgrading of reaction systems of Co-based catalysts for ECO2 RR, are also discussed.