The TM-based borides and boron oxides, which are abundant and provide economically attractive alternatives, showed promising catalytic performance for water splitting. Central to this class of materials is cobalt boride with moderate HER activity. Cobalt boride (CoxB)based materials take advantage of the fact that Co as first-row transition metal possesses three unoccupied d-orbitals facilitating facile surface chemical interactions. Metalloids such as boron and phosphorus have been known to influence the electronic configuration of the metal sites. Electron-deficient borides have been employed to shift electrons towards the vacant d-orbitals of the active Co sites, to beneficially affect the electron transfer between the reactant and the catalyst, and further to increase the reduction reaction kinetics. In amorphous CoxB-based materials reverse electron transfer shifts electron density from B to Co thereby creating electron-rich Co sites which enhances Co interactions with protons leading to enhanced HER. Incorporation of phosphorous into a CoxB system directly modulates the electron density around cobalt atoms, which impacts electron transfer and the hydrogen interaction with the active sites. Despite the considerable progress made in the development of efficient cobalt boride-based electrocatalysts, advanced synthesis strategies affording the tailored cobalt chemistry, modulation of the electronic nature of cobalt and advanced phase engineering at the nanoscale for HER are crucial. Besides the careful choice of a performant material system, the global and, more importantly, local crystal structure of the chosen system plays a significant role in determining its catalytic performance. Amorphous systems inherently possess dangling bonds randomly oriented in space, which results in a higher degree of unsaturated electronic configurations. Consequently, purely amorphous catalysts possess a large fraction of unsaturated active sites facilitating efficient adsorption and surface reactions at the cost of conductivity. In contrast, crystalline phases enhance the material's intrinsic conductivity. It is therefore necessary to produce catalysts, which take advantage of the synergistic effect of complex heterostructures consisting of crystalline and amorphous phases at the nanoscale. TMboride catalysts are typically synthesized via chemical reduction reactions of transition metal cations in aqueous solution using alkali metal tetrahydrides as reducing agent and a boron source to precipitate metal-borides. However, this reaction is spontaneous and it is a challenge to control the final products. Such products are mostly amorphous, and typically require post-thermal treatment to induce some form of crystallinity or utilize highly conductive carbon to enhance the electrocatalytic performance. TM-boride-based nanomaterials, therefore, provide a suitable platform for phase engineering at the nanoscale to develop efficient HER electrocatalysts with unique chemistry, morphology, and unconventional mixed crystalline-amorphous phases using only a facile and cost-effective wet-chemical reduction process. Herein, we use an elaborate synthesis strategy to develop a series of self-supported, amorphouscrystalline (heterostructured), nanostructured cobalt boride phosphite electrocatalysts. Our synthesis technique avoids any additional energy-intensive annealing process as commonly employed to induce crystallinity in TM-boride based catalysts synthesized in an aqueous reducing solution. Moreover, it overcomes the use of binders, such as Nafion, to stabilize the catalyst, enabling improved mass transport, enhanced access to active sites, less interfacial resistance, and higher electrical conductivity without adding carbon nanomaterials.