Phosphate Doped Ultrathin FeP Nanosheets as Efficient Electrocatalysts for the Hydrogen Evolution Reaction in Acid Media

Nickel Iron Phosphide/Phosphate as an Oxygen Bifunctional Electrocatalyst for High-Power-Density Rechargeable Zn-Air Batteries

The evolution of an effective oxygen electrocatalyst is of great importance for the widespread application of Zn-air batteries but remains an immense challenge. Thus, an efficient catalyst toward the oxygen evolution reaction and oxygen reduction reaction (OER and ORR) is highly essential for high-performance Zn-air batteries. Here, we have reported bifunctional nickel iron phosphide/phosphate (NiFeP/Pi) catalysts with various Ni/Fe ratios toward oxygen electrocatalysis in alkaline media. These catalysts are highly active toward OER and ORR, wherein NiFe(1:2)P/Pi exhibits a low OER overpotential of 0.21 V at 10 mA cm-2 and a high ORR onset potential (0.98 V vs RHE) with the lowest potential difference (ΔE = E10 - E1/2) of 0.62 V, which surpasses that of the benchmark Pt/C and RuO2 catalyst as well as those of most previously reported bifunctional catalysts. Furthermore, the NiFe(1:2)P/Pi-based Zn-air battery demonstrates a very high power density of 395 mW cm-2 and outstanding discharge capacity of 900 mAh g-1@10 mA cm-2 along with steady cyclability, maintaining 98% of the round trip efficiency over 300 cycles. These results are helpful for a good understanding of the composition-activity relation with a certain band gap toward high-performance Zn-air batteries.

Activating Titanium Metal with H2 Plasma for the Hydrogen Evolution Reaction

Developing a high-performance nonprecious metal electrocatalyst for water splitting is a strong demand for the large-scale application of electrochemical H₂ production. In this work, we design a facile and scalable strategy to activate titanium metal for the hydrogen evolution reaction (HER) in alkaline media through incorporating hydrogen into the α-Ti crystal lattice by H₂ plasma bombardment. Benefiting from the accelerated charge transfer and enlarged electrochemical surface area after H₂ plasma treatment, the H-incorporated Ti shows remarkably enhanced HER activity with a much lower overpotential at -10 mA cm^-2 by 276 mV when compared to the pristine Ti. It is revealed that the retention of the incorporated H(D) atoms in the Ti crystal lattice during HER accounts for the durable feature of the catalyst. Density functional theory calculations demonstrate the effectiveness of hydrogen incorporation in tuning the adsorption energy of reaction species via charge redistribution. Our work offers a novel route to activate titanium or other metals by H incorporation through a controllable H₂ plasma treatment to tune the electronic structure for water splitting reactions.

The Efficient Photocatalytic Degradation of Organic Pollutants on the MnFe2O4/BGA Composite under Visible Light

The MnFe₂O₄/BGA (boron-doped graphene aerogel) composite was prepared by hydrothermal treatment of MnFe₂O₄ particles, boric acid, and graphene oxide. When applied as a photo-Fenton catalyst for the degradation of rhodamine B, the MnFe₂O₄/BGA composite yielded a degradation efficiency much higher than the sum of those of individual MnFe₂O₄ and BGA under identical experimental conditions, indicating a strong synergetic effect established between MnFe₂O₄ and BGA. The catalytic degradation of rhodamine B was proved to follow pseudo first-order kinetics, and the apparent reaction rate constant on the MnFe₂O₄/BGA composite was calculated to be three- and seven-fold that on BGA and MnFe₂O₄, respectively. Moreover, the MnFe₂O₄/BGA composite also demonstrated good reusability and could be reused for four cycles without obvious loss of photocatalytic activity.

FeCoP2 Nanoparticles Embedded in N and P Co-doped Hierarchically Porous Carbon for Efficient Electrocatalytic Water Splitting

The design and synthesis of low-cost and efficient bifunctional electrocatalysts for water splitting are critical and challenging. Hereby, a bimetallic phosphide embedded in a N and P co-doped porous carbon (FeCoP₂@NPPC) material was synthesized by using sustainable biomass-derived N- and P-containing carbohydrates and non-noble metal salts as precursors. The obtained material exhibits good catalytic activities in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water splitting. The bimetallic alloy phosphide (FeCoP₂) is the active site for electrocatalysis. Theoretical calculation indicates that the sub-layer Fe atoms and top-layer Co atoms in FeCoP₂ exhibit a synergistic effect for enhanced electrocatalytic performance. The carbon matrix around the FeCoP₂ can prevent the corrosion during the catalytic reactions. The hierarchically porous structure of the FeCoP₂@NPPC material can promote the transfer of electrons and electrolyte, and increase the contact area of the active sites and electrolytes. N- and P-containing functionalities improve the wetting and conductivity properties of the porous carbon. Due to the synergistic effects, FeCoP₂@NPPC requires a low overpotential of 114 and 150 mV at the current density of 10 mA cm^-2 for HER in 0.5 M H₂SO₄ and 1.0 M KOH, and an overpotential of 236 mV for OER in 1.0 M KOH solution, which are much lower than those of FeP@NPPC and CoP@NPPC. Based on the density functional theory calculation, FeCoP₂ yields the smallest Gibbs free energy change of rate-determining step among the samples, which leads to better electrochemical performances. In addition, when FeCoP₂@NPPC was used as a bifunctional catalyst in water splitting, the electrolyzer needed a low voltage of 1.60 V to deliver the current density of 10 mA cm^-2. Furthermore, this work provides a strategy for preparing sustainable, stable, and highly active electrocatalysts for water splitting.

MoSx on Nitrogen-Doped Graphene for High-Efficiency Hydrogen Evolution Reaction: Unraveling the Mechanisms of Unique Interfacial Bonding for Efficient Charge Transport and Stability

Functional nanostructures with abundant exposed active sites and facile charge transport through conductive scaffolds to active sites are pivotal for developing an advanced and efficient electrocatalyst for water splitting. In the present study, by coating ∼3 nm MoS_x on nitrogen-doped graphene (NG) pre-engrafted on a flexible carbon cloth (MNG) as a model system, an extremely low Tafel slope of 39.6 mV dec^-1 with cyclic stability up to 5000 cycles is obtained. The specific fraction of N on the NG framework is also analyzed by X-ray photoelectron spectroscopy and X-ray absorption near edge spectroscopy with synchrotron radiation light sources, and it is found that the MoS_x particles are selectively positioned on the specific graphitic N sites, forming the unique Mo-N-C bonding state. This Mo-N-C bonding is founded to facilitate highly effective charge transfer directly to the active sulfur sites on the edges of MoS_x, leading to a highly improved hydrogen evolution reaction (HER) with excellent stability (95% retention @ 5000 cycles). The functional anchoring of MoS_x by such bonding prevents particle aggregation, which plays a significant role in maintaining the stability and activity of the catalyst. Furthermore, it has been revealed that MNG samples with adequately high amounts of both pyridinic and graphitic N result in the best HER performance. This work helps in understanding the mechanisms and bonding interactions within various catalysts and the scaffold electrode.