Producing hydrogen in-situ to be used with polymer electrolyte membrane (PEM) fuel cells for on-board or combined heat & power applications, has gathered significant research efforts in the last few decades for making cleaner and energy efficient systems. Packed bed design had been conventionally deployed in methanol steam reformers used for the purpose. Due to low thermal conductivity of the catalyst bed with void fraction, steep temperature gradients are observed across the bed. This heat transfer limitation leads to a trade-off between attaining either high methanol conversion (which is endothermic) or low CO production, which is a poison to PEM fuel cells. Various researchers have attempted to minimize the heat transfer resistance by various techniques such as inserting flow distribution elements in the packed bed, designing plate-type reformers, and internally heated metal monolith reformer besides others. These designs helped reduce the thermal gradients along the length of the reformer and improved methanol conversion to a certain extent. If the catalyst is coated on the wall of the reactor, then the catalyst temperature would be almost equal to the wall temperature minimizing thermal resistance and solving the trade-off problem. However, application of wall-coated reactors is so far restricted to microreactors, that can process only low flow capacities. In this work, a wall-coated, integrated reformer-combustor design based on Hilbert’s space-filling-curve with high surface to volume ratio is proposed. A CFD model of the proposed Hilbert’s reactor (HR) was developed. Extensive simulations were performed to evaluate the relative influences of fluid flow, heat transfer, mass transfer and reaction kinetics on the overall reactor performance. The HR reformer was predicted to achieve about 84% methanol conversion with less than 2% CO production for a coupled 5kWe LTPEM fuel cell capacity. For the experimental proof-of-concept of the milli-scale wall coated HR reactor, a single channel wall-coated reformer and combustor was designed and fabricated. Systematic experiments were performed and the results were used to develop kinetic models representing catalytic hydrogen combustion and methanol steam reforming in the milli-scale wall coated reactor configuration. These models were further used to perform CFD simulations of single channel reactor, that confirmed the characteristic results of the HR reactor.