Topotactical Hydrogen Induced Single-Band $d$-wave Superconductivity in La${}_2$NiO${}_4$

La${}_2$NiO${}_4$ is an antiferromagnetic insulator with a structural resemblance to its cuprate counterpart, La${}_2$CuO${}_4$. However, La${}_2$CuO${}_4$ has a Cu${}^{2+}$ or 3$d^9$ electronic configuration that needs to be hole or electron doped for superconductivity, whereas La${}_2$NiO${}_4$ is 3$d^8$ with divalent Ni${}^{2+}$. Making a cuprate analog through conventional electron doping is impractical due to the rarity of tetravalent substituents for trivalent La. Here, we propose an alternative route: intercalating topotactical hydrogen, which is possible through electric-field-controlled protonation and transforms La${}_2$NiO${}_4$ into a 3$d_{x^2-y^2}$ single-band two-dimensional antiferromagnetic Mott insulator analogous to La${}_2$CuO${}_4$. This we find through density-functional theory and dynamical mean-field theory calculations. The furthergoing dynamical vertex approximation predicts that H-La${}_2$NiO${}_4$ can host $d$-wave superconductivity under 15% hole doping with a critical temperature above 20,K. Our findings not only suggest a new method for tuning the electronic structure of layered nickelates but also provide theoretical evidence for a new nickelate superconductor, awaiting experimental synthesis.