Efficient Hydrogen Evolution Electrocatalysis Using Cobalt Nanotubes Decorated with Titanium Dioxide Nanodots

Electrodeposition of Nickel Nanoparticles for the Alkaline Hydrogen Evolution Reaction: Correlating Electrocatalytic Behavior and Chemical Composition

Ni nanoparticles (NPs) consisting of Ni, NiO, and Ni(OH)₂ were formed on Ti substrates by electrodeposition as electrocatalysts for the hydrogen evolution reaction (HER) in alkaline solution. Additionally, the deposition parameters including the potential range and the scan rate were varied, and the resulting NPs were investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. The chemical composition of the NPs changed upon using different conditions, and it was found that the catalytic activity increased with an increase in the amount of NiO. From these data, optimized NPs were synthesized; the best sample showed an onset potential of approximately 0 V and an overpotential of 197 mV at a cathodic current density of 10 mA cm^-2 as well as a small Tafel slope of 88 mV dec^-1 in 1 m KOH, values that are comparable to those of Pt foil. These NPs consist of approximately 25 % Ni and Ni(OH)₂ each, as well as approximately 50 % NiO. This implies that to obtain a successful HER electrocatalyst, active sites with differing compositions have to be close to each other to promote the different reaction steps. Long-time measurements (30 h) showed almost complete transformation of the highly active catalyst compound consisting of Ni⁰ , NiO, and Ni(OH)₂ into the less active Ni(OH)₂ phase. Nevertheless, the here-employed electrodeposition of nonprecious metal/metal-oxide combination compounds represents a promising alternative to Pt-based electrocatalysts for water reduction to hydrogen.

Co2P quantum dot embedded N, P dual-doped carbon self-supported electrodes with flexible and binder-free properties for efficient hydrogen evolution reactions

Transition metal phosphides (TMPs) are considered to be superb catalysts for water splitting. In this work, we introduce an efficient strategy to fabricate dicobalt phosphide (Co₂P) quantum dots embedded in N, P dual-doped carbon (Co₂P@NPC) on carbon cloth (Co₂P@NPC/CC) by in situ carbonization of cobalt ion induced phytic acid (PA) and polyaniline (PANI) macromolecule precursors. As a highly efficient self-supported electrode, it has a low onset overpotential (74 mV at 1 mA cm^-2) approaching that of the commercial Pt/C catalyst for the hydrogen evolution reaction (HER) in acidic media. Meanwhile, it also shows very low overpotentials of only 116 and 129 mV at 10 mA cm^-2 with robust stability in acidic and alkaline media, respectively.

Electrocatalysts for Hydrogen Evolution in Alkaline Electrolytes: Mechanisms, Challenges, and Prospective Solutions

Hydrogen evolution reaction (HER) in alkaline medium is currently a point of focus for sustainable development of hydrogen as an alternative clean fuel for various energy systems, but suffers from sluggish reaction kinetics due to additional water dissociation step. So, the state-of-the-art catalysts performing well in acidic media lose considerable catalytic performance in alkaline media. This review summarizes the recent developments to overcome the kinetics issues of alkaline HER, synthesis of materials with modified morphologies, and electronic structures to tune the active sites and their applications as efficient catalysts for HER. It first explains the fundamentals and electrochemistry of HER and then outlines the requirements for an efficient and stable catalyst in alkaline medium. The challenges with alkaline HER and limitation with the electrocatalysts along with prospective solutions are then highlighted. It further describes the synthesis methods of advanced nanostructures based on carbon, noble, and inexpensive metals and their heterogeneous structures. These heterogeneous structures provide some ideal systems for analyzing the role of structure and synergy on alkaline HER catalysis. At the end, it provides the concluding remarks and future perspectives that can be helpful for tuning the catalysts active-sites with improved electrochemical efficiencies in future.

Interface engineering of a CeO2-Cu3P nanoarray for efficient alkaline hydrogen evolution

It is of great importance to design and develop highly active electrocatalysts for the hydrogen evolution reaction (HER) under alkaline conditions. In this work, we report the development of a CeO₂-Cu₃P nanoarray supported on nickel foam (CeO₂-Cu₃P/NF) as an excellent HER catalyst with the demand of an overpotential of only 148 mV to deliver a geometrical catalytic current density of 20 mA cm^-2 in 1.0 M KOH. Remarkably, this catalyst also shows strong long-term electrochemical durability for at least 100 h with nearly 100% Faradaic efficiency. Density functional theory calculations reveal that the CeO₂-Cu₃P/NF hybrid has a lower water dissociation energy and a more thermo-neutral hydrogen adsorption free energy.

Enhanced electrocatalysis for alkaline hydrogen evolution by Mn doping in a Ni3S2 nanosheet array

Mn-Ni₃S₂/NF exhibits enhanced catalytic HER performance and demands an overpotential of 152 mV to afford 10 mA cm⁻² in 1.0 M KOH.

Cathodic electrochemical activation of Co3O4 nanoarrays: a smart strategy to significantly boost the hydrogen evolution activity

The room-temperature cathodic polarization of Co₃O₄ leads to an ultrathin amorphous Co–P shell as an active layer. Such a Co–P@Co₃O₄ hybrid nanoarray needs an overpotential of 73 mV to drive a geometrical catalytic current density of 10 mA cm⁻² in 1.0 M KOH.

Fabrication of strong bifunctional electrocatalytically active hybrid Cu–Cu2O nanoparticles in a carbon matrix

Earth-abundant copper-based hybrid Cu–Cu₂ONPs@C in the carbon matrix exhibited enhanced OER and HER catalytic activity compared to pure Cu₂O and CuNPs@C.

High-performance alkaline hydrogen evolution electrocatalyzed by a Ni3N–CeO2 nanohybrid

A Ni₃N–CeO₂/TM nanohybrid shows high activity and durability for the alkaline hydrogen evolution reaction, offering 10 mA cm⁻² at an overpotential of 80 mV.

Holey Reduced Graphene Oxide Coupled with an Mo2 N-Mo2 C Heterojunction for Efficient Hydrogen Evolution

An in situ catalytic etching strategy is developed to fabricate holey reduced graphene oxide along with simultaneous coupling with a small-sized Mo₂ N-Mo₂ C heterojunction (Mo₂ N-Mo₂ C/HGr). The method includes the first immobilization of H₃ PMo₁₂ O₄₀ (PMo₁₂ ) clusters on graphite oxide (GO), followed by calcination in air and NH₃ to form Mo₂ N-Mo₂ C/HGr. PMo₁₂ not only acts as the Mo heterojunction source, but also provides the Mo species that can in situ catalyze the decomposition of adjacent reduced GO to form HGr, while the released gas (CO) and introduced NH₃ simultaneously react with the Mo species to form an Mo₂ N-Mo₂ C heterojunction on HGr. The hybrid exhibits superior activity towards the hydrogen evolution reaction with low onset potentials of 11 mV (0.5 m H₂ SO₄ ) and 18 mV (1 m KOH) as well as remarkable stability. The activity in alkaline media is also superior to Pt/C at large current densities (>88 mA cm^-2 ). The good activity of Mo₂ N-Mo₂ C/HGr is ascribed to its small size, the heterojunction of Mo₂ N-Mo₂ C, and the good charge/mass-transfer ability of HGr, as supported by a series of experiments and theoretical calculations.

Molybdenum Disulfide-Black Phosphorus Hybrid Nanosheets as a Superior Catalyst for Electrochemical Hydrogen Evolution

Engineering electronic properties is a promising way to design nonprecious-metal or earth-abundant catalysts toward hydrogen evolution reaction (HER). Herein, we deposited catalytically active MoS₂ flakes onto black phosphorus (BP) nanosheets to construct the MoS₂-BP interfaces. In this case, electrons flew from BP to MoS₂ in MoS₂-BP nanosheets because of the higher Fermi level of BP than that of MoS₂. MoS₂-BP nanosheets exhibited remarkable HER performance with an overpotential of 85 mV at 10 mA cm^-2. Due to the electron donation from BP to MoS₂, the exchange current density of MoS₂-BP reached 0.66 mA cm^-2, which was 22 times higher than that of MoS₂. In addition, both the consecutive cyclic voltammetry and potentiostatic tests revealed the outstanding electrocatalytic stability of MoS₂-BP nanosheets. Our finding not only provides a superior HER catalyst, but also presents a straightforward strategy to design hybrid electrocatalysts.

A Mn-doped Ni2P nanosheet array: an efficient and durable hydrogen evolution reaction electrocatalyst in alkaline media

A Mn-doped Ni₂P nanosheet array on nickel foam (Mn-Ni₂P/NF) acts as a high-efficiency and durable electrocatalyst for the hydrogen evolution reaction in 1.0 M KOH, driving 20 mA cm⁻² at an overpotential of 103 mV, which is 82 mV less than that for Ni₂P/NF.

Ru decorated with NiCoP: an efficient and durable hydrogen evolution reaction electrocatalyst in both acidic and alkaline conditions

NiCoP@Ru is an excellent hydrogen evolving catalyst in both acidic and alkaline conditions, close in performance to that of Pt/C.