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...
