Metal Boride‐Based Catalysts for Electrochemical Water‐Splitting: A Review

Abstract

Electrocatalytic water-splitting has gained a firm hold in the area of renewable hydrogen production owing to its integrative compatibility with intermittent energy sources. However, wide-scale implementation of this technology demands discovery of new electrode materials that strike a good balance between efficiency, stability, and cost. In the pool of inexpensive electrodes capable of catalyzing hydrogen and oxygen evolution reactions, metal borides/ borates have made a big splash in the last decade. However, the research in this family of electrocatalysts remains unorganized owing to the diversity of reports. This review summarizes the past and present research progress in metal borides/borates for electrocatalytic water-splitting. The fundamental reasons for electrochemical behavior in different metal borides/borates are highlighted here, also including some comments regarding erroneous practices in the performance evaluation of metal borides/borates. Various strategies used to enhance the electrocatalytic performance of metal borides/borates are discussed in detail. Different methods evolved over the years for the synthesis of metal borides/ borates are also discussed. Finally, an assessment of the commercial viability of metal borides/borates is made and future research directions are suggested. multimetal oxides, [18,19] layered double hydroxides, [20] oxyhydroxides, [21] and perovskites. [13,18] In addition to these, there has been the family of transition-metal borides/borates that have garnered enormous interest in the recent past. Though transition-metal borides (TMBs) have been used for water electrolysis since many decades, they were not really seen as potential candidates to replace noble metal catalysts, until recently. Indeed, in 2009, the group of Daniel Nocera reported in situ formed Co [22] and Ni [23] borates as analogous catalysts to Co phosphate, [24] for near-neutral water-splitting. Later, the groups of Hu [25] and Patel [26] reported development of Mo boride and Co boride, respectively, for electrocatalytic water splitting. Following these reports, transition-metal borides/ borates [27][28][29][30][31][32] were developed using various techniques and were used extensively for water-splitting reactions, in different pH solutions. Here, we would like to inform the readers that usually boron-based catalysts that are developed in situ using electrodeposition are referred to as "borates" (denoted as M-B i , M = metal) while those catalysts prepared by any other technique are referred to as "borides" (denoted as M-B). Over the past 5-6 years, a lot of studies have been carried out on borides/borates with remarkable results, presenting new possibilities in search for non-noble electrocatalysts. The electrochemical performance, stability and other important properties of all the metal borides reported so far are enlisted in Table 1 while that of metal borates are listed in Table 2. However, there are a lot of aspects that are not yet understood completely about borides/borates. For instance, the o...

Alkaline Water Oxidation Using a Bimetallic Phospho‐Boride Electrocatalyst

“…[3][4][5][6][7] Layered double hydroxides (LDHs) of these transition metals have even surpassed the most active and stable IrO 2 and RuO 2 catalysts, largely due to their higher surface areas, but in turn suffer from poor conductivity. [8,9] In addition to these, compounds of transition metals in the form of phosphides, [10,11] sulfides, [12,13] borides, [14,15] selenides, [16,17] nitrides, [18,19] and carbides [20,21] have emerged as promising low-cost alternatives. In majority of the cases, these compounds are proposed to act as pre-catalysts that transform into reactive oxy-hydroxy (*OOH) species on the surface during OER, while still providing conducting pathways through the core.…”

Amorphous‐crystalline Co−B−P Catalyst for Synergistically Enhanced Hydrogen Evolution Reaction

“…Electrochemical active surface area (ECSA) is a parameter that measures the effective active sites on the catalyst surface. ECSA has a close relationship with the double‐layer capacitor formed between the electrode and electrolyte [5c] . The CV curves for Co−B 400 , Co−P and Co−B−P at increasing scan rates of 10–100 mV s −1 were illustrated in Figure S8.…”

Electroless Plating of Transition Metal Boride with High Boron Content as Superior HER Electrocatalyst

“…However, the lack of practical electrode with high efficiency and low cost hinders the large‐scale application of this technology . Recently, transition metal boride (TMB) electrocatalysts have attracted intensive attentions because of earth abundance, low cost, easy fabrication and their sufficient activities to facilitate hydrogen evolution reaction (HER) and/or oxygen evolution reaction (OER) …”