Understanding the Surface Reconstruction on Ternary W_xCoB_x for Water Oxidation and Zinc–Air Battery Applications

Abstract

The catalysts used to decrease the overpotential for this reaction play a pivotal role in realizing these devices. [2] Currently, iridium (Ir) and ruthenium (Ru) based oxides have been used as efficient OER catalysts. However, the scarcity and price of these materials makes them unsuitable for large-scale applications such that they need to be replaced with low-cost nonprecious metal electrocatalysts. [3] Many transition metal-based materials are promising alternatives to promote OER in alkaline media. Among the earth-abundant elements, cobalt was found to be one of the best alternatives to replace noble metals for OER. Cobalt derivatives are widely investigated as OER catalysts, including their oxides, [4] nitrides, [5,6] selenides, [7] borides, [8] carbides, [9] and phosphides. [10] The surfaces of these materials are known to undergo in situ transformations at Co sites to form cobalt oxyhydroxide (CoOOH) under the electric potential applied during the water oxidation process. [11] This surface reconstruction process directly determines the final performance of the catalysts. For instance, Duan et al., reported the controllable anodic leaching of Cr in CoCr 2 O 4 by activating the pristine material at high potential, which enables the transformation of the inactive CoCr 2 O 4 spinel into a highly Here, the synthesis of a series of pure phase metal borides is reported, including WB, CoB, WCoB, and W 2 CoB 2 , and their surface reconstruction is studied under the electrochemical activation in alkaline solution. A cyclic voltammetric activation is found to enhance the activity of the CoB and W 2 CoB 2 precatalysts due to the transformation of their surfaces into the amorphous CoOOH layer with a thickness of 3-4 nm. However, such surface transformation does not happen on the WB and WCoB due to their superior structure stability under the applied voltage, highlighting the importance of metal components for the surface reconstruction process. It is found that, compared with CoB, the W 2 CoB 2 surface shows a quicker reconstruction with a larger active surface area due to the selective leaching of the W from its surface. In the meantime, the metallic W 2 CoB 2 core underneath the CoOOH layer shows a better promotion of its oxygen evolution reaction (OER) performance than CoB. Therefore, the ternary W 2 CoB 2 shows better OER performance than the CoB, as well as the WB and WCoB. It is also found that the mixture of W 2 CoB 2 with Pt/C as the catalysts in air electrode for rechargeable Zn-air battery (ZAB), shows better performance than the IrO 2 -Pt/C couple-based ZAB.

Exploring the Role of Multi-Catalytic Sites in an Amorphous Co–W–B Electrocatalyst for Hydrogen and Oxygen Evolution Reactions

“…It must be noted that this peak position is positively shifted by ∼0.8 eV as compared to elemental B, which is characteristic of the “reverse electron transfer” phenomenon observed in ATMBs. , The other peak at 192.1 eV is assigned to oxidized boron states. The deconvoluted W 4f (Figure i) peaks positioned at 31.3 and 33.4 eV represent metallic W (0) with a characteristic energy spacing of ∼2.1 eV between the W 4f 7/2 and W 4f 5/2 spin–orbit components, while the higher BE peaks at 35.3 and 37.4 eV correspond to tungsten oxide. , The presence of oxidized species in all the elements is attributed to the exposure of the catalysts to the ambient atmosphere before the XPS measurements.…”

“…The deconvoluted W 4f (Figure 1i) peaks positioned at 31.3 and 33.4 eV represent metallic W (0) with a characteristic energy spacing of ∼2.1 eV between the W 4f 7/2 and W 4f 5/2 spin−orbit components, while the higher BE peaks at 35.3 and 37.4 eV correspond to tungsten oxide. 27,45 The presence of oxidized species in all the elements is attributed to the exposure of the catalysts to the ambient atmosphere before the XPS measurements.…”

“…These similarities suggest that Co–W–B must also possess similar HER (and OER) rates as Co–Mo–B. Recently, there have been a couple of reports exploring the HER and OER activities of crystalline W–Co–B compounds with interesting results. − For instance, Saad et al . reported crystalline W 2 CoB 2 for alkali OER with η 10 = 274 mV and explained the effect of surface reconstruction on the OER performance.…”

“…Recently, there have been a couple of reports exploring the HER and OER activities of crystalline W−Co−B compounds with interesting results. 27−29 For instance, Saad et al 27 reported crystalline W 2 CoB 2 for alkali OER with η 10 = 274 mV and explained the effect of surface reconstruction on the OER performance. In crystalline compounds, identification of the active centers is easier owing to a defined crystal structure.…”

Nanoneedles of Mixed Transition Metal Phosphides as Bifunctional Catalysts for Electrocatalytic Water Splitting in Alkaline Media

“…In this work, we changed their chemical environment by preparing a series of mixed compounds (Ni/Co and Ni/Fe) to understand their reciprocal interaction and synergic effects. The interaction of different metals in close contact is an approach used to overcome the OER slow kinetics for water electrolysis and metal–air batteries [ 18 , 19 , 20 , 21 , 22 ]; this approach is also the founding principle of the chemical activity of high-entropy materials [ 23 ]. The combination of Ni and Co has been deeply investigated for HER, where the synergy among the catalytic properties of Ni, which lowers the HER over-potential, and Co, which increases the hydrogen adsorption, is realized and allows to obtain a larger value of exchange current density [ 24 ].…”