ZrB2-HfB2 solid solutions as electrode materials for hydrogen reaction in acidic and basic solutions

Abstract

Spark plasma sintered transition metal diborides such as HfB 2 , ZrB 2 and their solid solutions were investigated as electrode materials for electrochemical hydrogen evolutions reactions (HER) in 1 M H 2 SO 4 and 1 M NaOH electrolytes. HfB 2 and ZrB 2 formed complete solid solutions when mixed in 1:1, 1:4, and 4:1 ratios and they were stable in both electrolytes. The HER kinetics of the diborides were slower in the basic solution than in the acidic solutions. The Tafel slopes in 1 M H 2 SO 4 were in the range of 0.15-0.18 V/decade except for pure HfB 2 which showed a Tafel slope of 0.38 V/decade. In 1 M NaOH the Tafel slopes were in the range of 0.12-0.27 V/decade. The composition of Hf x Zr 1-x B 2 solid solutions with x = 0.2-0.8, influenced the exchange current densities, overpotentials and Tafel slopes of the HER. The EIS data were fitted with a porous film equivalent circuit model in order to better understand the HER behavior. In addition, modeling calculations, using density functional theory approach, were carried out to estimate the density of states and band structure of the boride solid solutions.

Partial Etching of Al from MoAlB Single Crystals To Expose Catalytically Active Basal Planes for the Hydrogen Evolution Reaction

“…MXenes are therefore potentially promising 2D HER catalysts, but are limited to carbide, nitride, and carbonitride phases due to compositional limitations of the parent MAX phases. In addition to metal carbides, metal borides also have been gaining attention as HER catalysts, − especially molybdenum borides that include α-MoB, β-MoB, Mo 2 B, and MoB 2 . , However, efforts to access high surface area metal boride materials are challenging, particularly for the molybdenum-based systems that are of greatest interest for their high activity and stability. The ability to access MXene-like 2D borides through etching boride analogues of MAX phases would significantly expand the diversity of available MXene materials .…”

Synthesis of medium-entropy (Zr_1/3Hf_1/3Ta_1/3)B₂ using the spark plasma consolidation of diboride powders

“…This step is required to preserve components from the reaction at the lower temperatures. 7), 14) For instance, Sitler et al 5) reported that solid-solution between ZrB 2 and HfB 2 can be obtained at temperatures as low as 1700°C. We prepared the binary equimolar solid-solution using similar conditions to ZHT20, to understand the formation of the ZHT diboride (Suppl 1).…”

Processing and Optical Behavior of Dense (Hf,Zr)B2 Solid Solutions for Solar Energy Receivers

“…By considering the high mutual solubility displayed by Zr-and Hfdiborides, the latter have been also combined in different proportions to form thermodynamically stable (Hf x Zr 1-x )B 2 solid solutions [5][6][7][8][9][10][11][12][13][14][15][16]. The methods proposed in the literature for their synthesis are chemical vapor deposition (CVD) [5,6], arc-melting [9], mechanically induced self-sustaining reaction [10], heat treatment of co-ball milled ZrB 2 and HfB 2 powders [11][12][13][14], molten salt route [15,16], carbothermal (CTR) and borohydride (BHR) reduction followed by flash sintering [7], and microwave co-assisted boro/carbothermal reduction [8]. Only few of them [7,[11][12][13][14] were addressed to the obtainment of bulk ceramics.…”