Date Published: October 20, 2018
Publisher: John Wiley and Sons Inc.
Author(s): Doudou Zhang, Jingying Shi, Yu Qi, Xiaomei Wang, Hong Wang, Mingrun Li, Shengzhong Liu, Can Li.
Nickel is regarded as the best alternative metal electrocatalyst to platinum for hydrogen evolution reaction (HER). Success in developing a quasi‐amorphous metallic nickel (QAMN) nanopowder catalyst using a two‐step chemical route for efficient and durable HER in alkaline solution is reported. It is found that the QAMN electrocatalyst exhibits essentially zero overpotential at the cathodic onset while delivering 10 mA cm−2 at an overpotential of only 240 mV; both performances are far better than what was reported previously using prior metallic nickel catalysts. Taking into account increased surface area, further enhanced activity is attributed to the superior intrinsic activity. Meanwhile, the QAMN catalyst shows excellent stability in accelerated and interrupted polarization in alkaline solution for tens of hours. This study provides a new chemical means to prepare amorphous metallic materials for more efficient catalysis.
Electrochemical hydrogen generation from water splitting powered by clean solar and wind electricity has been regarded as one of the most promising approaches to store the intermittent renewable energy.1, 2 Extensive efforts have been made on the alkaline electrolysis since this technology is able to offer high purity hydrogen with great promise for large‐scale production at low cost.3 In fact, most of the electrochemical water splitting devices used to generate hydrogen in a few limited commercial applications such as metallurgy, semiconductor processing, glass cutting, acrylic polishing, etc. are based on alkaline electrolysis technology. However, in alkaline solution, the rate for hydrogen evolution reaction (HER) is at least two orders of magnitude slower than that in acidic environment, which is a great drawback for the alkaline electrolysis.4, 5, 6, 7 Moreover, it needs to use very noble metal (platinum) HER electrocatalysts to attain low overpotential at the onset and rapid current increase with the voltage applied.8, 9, 10, 11 To achieve effective hydrogen generation at affordable cost, it is of crucial importance to develop an effective electrocatalyst using earth‐abundant elements for the hydrogen production in alkaline solution.
The metallic nickel nanopowder was synthesized by a two‐step chemical route as schematically illustrated in Figure1. The (Mo, W)‐doped hydrotalcite‐like basic nickel carbonate was prepared by ion exchanging for precursor materials. The feeding nickel, molybdenum, and tungsten in atomic ratio were set at 1:0.4:x (x = 0, 0.05, 0.07, 0.1, 1.0). In the first, the powder‐like oyster yellow precursors were heated at 400 °C in air for 2 h to generate powders in brown. Secondly, the brown powders were further annealed at 600 °C under a continuous flow of ammonia gas and the black powders were collected for characterization and fabrication of electrocatalyst.
In conclusion, we successfully developed a chemical route for the systhesis of quasi‐amorphous nickel metal catalysts, which exhibits superior alkaline HER activity with cathodic onset potential approaching 0 mV and overpotential required as low as 240 mV to deliver current density of 10 mA cm−2. The QAMN also demonstrates the robust performance in sustaining or intermittent polarization for tens of hours. In addition to the increasing ECSA, the enhancement in the intrinsic activity is the primary reason for the outstanding HER performance of the QAMN compared with its crystalline phase catalyst. This study affords a new strategy to prepare QAMN catalysts with great promise for efficient water electrolysis.
The authors declare no conflict of interest.