Electrocatalytic Water Splitting: From Harsh and Mild Conditions to Natural Seawater

Copper Incorporated Molybdenum Trioxide Nanosheet Realizing High-Efficient Performance for Hydrogen Production

The development of highly active non-precious metal electrocatalysts is crucial for advancing the practical application of hydrogen evolution reaction (HER). Doping engineering is one of the important strategies to optimize the electrocatalytic activity of electrocatalysts. Herein, we put forward a simple strategy to optimize the catalytic activity of MoO3 material by incorporating the Cu atoms into the interlayer (denoted as Cu-MoO3). The prepared Cu-MoO3 nanosheet has a larger surface area, higher conductivity, and strong electron interactions, which contributes to optimal reaction kinetics of the HER process. As a result, the Cu-MoO3 nanosheet only needs a small overpotential of 106 mV to reach the geometric current density of 10 mA cm−2. In addition, it also delivers a low Tafel slope of 83 mV dec−1, as well as high stability and Faraday efficiency. Notably, when using the Cu-MoO3 as a cathode to construct the water electrolyzer, it only needs 1.55 V to reach the 10 mA cm−2, indicating its promising application in hydrogen generation. This work provides a novel type of design strategy for a highly active electrocatalyst for an energy conversion system.

Stochastic Local Breakdown of Oxide Film on Ni from Identical-Location Imaging: One Single Site at a Time

The electrochemical breakdown of a metal oxide film can directly affect the performance of functional electrochemical devices. However, revealing the structural insight into the breakdown sites is challenging because of heterogeneity: different breakdown sites are spatially distributed over the surface. Herein, we combine scanning electrochemical cell microscopy with identical-location microscopies to reveal the heterogeneity in the breakdown of NiO film on Ni in a site-by-site manner. Local critical breakdown potential varies by ∼500 mV, corresponding to an excess energy of 0.02-0.12 J/m². Correlative composition imaging using time-of-flight secondary ion mass spectrometry shows Ni crystal grains with thinner NiO films are more resistant to breakdown. This high resistance is explained using classical nucleation theory, where the electrical energy is affected by the film thickness through the local interfacial capacitance. The correlative imaging approach overcomes the issue of heterogeneity, providing conclusive insight into the stability of the electrochemical interfaces.

Highly Durable and Efficient Ni-FeOx/FeNi3 Electrocatalysts Synthesized by a Facile In Situ Combustion-Based Method for Overall Water Splitting with Large Current Densities

Ni-/Fe-based materials are promising electrocatalysts for the oxygen evolution reaction (OER) but usually are not suitable for the hydrogen evolution reaction (HER). Herein, a durable and bifunctional catalyst consisting of Ni-FeO_x and FeNi₃ is prepared on nickel foam (Ni-FeO_x/FeNi₃/NF) by in situ solution combustion and subsequent calcination to accomplish efficient alkaline water splitting. Density functional theory (DFT) calculation shows that the high HER activity is attributed to the strong electronic coupling effects between FeO_x and FeNi₃ in the Janus nanoparticles by modulating ΔG_H* and electronic states. Consequently, small overpotentials (η) of 71 and 272 mV in HER and 269 and 405 mV in OER yield current densities (j) of 50 and 1000 mA cm^-2, respectively. The catalyst shows outstanding stability for 280 and 200 h in HER and OER at a j of ∼50 mA cm^-2. Also, the robustness and mechanical stability of the electrode at an elevated j of ∼500 mA cm^-2 are excellent. Moreover, Ni-FeO_x/FeNi₃/NF shows excellent water splitting activities as a bifunctional catalyst as exemplified by j of 50 and 500 mA cm^-2 at cell voltages of 1.58 and 1.80 V, respectively. The Ni-FeO_x/FeNi₃/NF structure synthesized by the novel, simple, and scalable strategy has large potential in commercial water electrolysis, and the in situ combustion method holds great promise in the fabrication of thin-film electrodes for different applications.

Electronic regulation of platinum species on metal nitrides realizes superior mass activity for hydrogen production

Developing high-active electrocatalyst to improve the efficiency of hydrogen evolution reaction (HER) is critical to achieve clean hydrogen. However, the low mass activity and high cost of this technology still limits its wide commercial application. Herein, a new kind of hybrid material is designed by introducing trace Pt species onto a mixed metal nitride matrixs (denoted as NiWN_x), presenting as an excellent electrocatalyst for HER. The prepared Pt-NiWN_x hybrid possesses abundant heterointerfaces, high conductivity and strong electron interactions, facilitating the reaction kinetics for hydrogen production. As a result, the Pt-NiWN_x only needs a small overpotential of 61 mV to reach the geometric current density of 100 mA cm^-2 in alkaline electrolyte. Notably, this kind of catalyst delivers a superior mass activity of 32.8 A mg_Pt^-1 at -0.1 V and high durability, exhibiting the promising prospects for industrial application. This work offers a novel design strategy for high-efficient hybrid materials for scaled hydrogen generation.